Is Thorium Our Energy Future? | Answers With Joe

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With the need for cleaner energy higher than ever before, could liquid fluoride thorium reactors be the solution?
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LINKS LINKS LINKS:
LFTR in 5 minutes
• LFTRs in 5 minutes - T...
Kirk Sorenson Ted Talk
• Thorium can give human...
Sci Show on LFTR
• Liquid Fluoride Thoriu...
Energy From Thorium
energyfromthorium.com/lftr-ove...
Thorium Myths
whatisnuclear.com/thorium-myt...
Triple Pundit Article
www.triplepundit.com/special/...
Worldwide Energy Data
yearbook.enerdata.net/electri...

[@tonychen76]

Joe, the three people who volunteered to turn the valve survive just fine. In 2005 one of them died from heart attack at the age of 65, and the other two were still alive as of 2016. The myth that they died heroically was based on incorrect info (probably due language barrier) that got blown up because it made a good story. That doesn't make them less heroic, because they did think it was a suicide mission. It just turned out that the radiation must have been far less dangerous than they expected.

[@joescott]

I actually made that exact point and then cut it for time (if you can believe this video was actually longer).

[@QualeQualeson]

Turns out that tiny bit of info was important hehe. In fact I had big problems absorbing the rest of the video cuz was left wondering what happened to them and also what I would do if asked :p Bottom line it's one of those irresistible human dramas and it needed some kind of closure.

[@artemkras]

Still, thousands died from radiation sickness or related diseases

[@texmex9721]

They survived because they were wearing Apollo space suits! I'm kidding! Well thank those men for their bravery, and I'm glad they all lived. How much radiation someone is exposed to is a tough thing to estimate in an emergency like that. And what effects any radiation has are also tough to estimate. But obviously it took brass balls to go into harms way.

[@tonychen76]

artemkras Err, no. That was what they think would happen. But it turned out that no, it didn't happen. Slightly over 6000 people got thyroid cancer, but because they were expecting it, they were diagnosed and treated early, and cancer is treatable when caught early. So a report from 20 years later concluded that actual death caused by Chernobyl is about 50-ish.

[@MrStarTraveler]

"uranium 233 can be used for bombs" - Theoretically yes; Physically yes; Practically No. A U-233 bomb was built and tested. And the whole ordeal showed that bombs based on u-233 are so unpractical that they are not worth it. It turns out that the strong gamma radiation: a) makes the process of building and storing the bomb extremely difficult. b) it makes it really difficult to conceal against an enemy, meaning the intense radiation can be detected from really far. c) the intense radiation leads to premature detonation that reduces the yield significantly. d) the bomb will decay. e) the intense radiation will degrade and eventually defunct any electronics within and around the bomb so no ICBM mounting...

[@jeremiahmitchell6420]

Wrong, it CAN be used. It's instability and low halflife discourages it's us by nuclear powers because they wish to maintain their stocks. Terrorists however,

[@davidhenry5128]

@MrStar traveler. Thank you for stating these facts, you did a better job than I would have.

[@davidhenry5128]

@Jeremiah Mitchell "Terrorists however" face the exact dificaulties, without the advanced equipment, facilities and expertise. Nuclear for terrorists amounts to what they can do with the waste that does not include nuclear bombs, LFTR reactors are a good way to eliminate most of that waste.

[@STSWB5SG1FAN]

@@davidhenry5128 Terrorists could still use it though, just not on the conventional means when someone thinks of an "atomic bomb". Any high toxic, highly radioactive material could be jacketed around a conventional explosive and used to contaminate a wide area, the "dirty bomb". One would just need the knowledge of when to remove the fuel from the reactor when it's at its most toxic level.

[@Validole]

@@STSWB5SG1FAN Current waste products are already in barrels on parking lots: just drive in, shoot the guards, load the barrels and scram. And they're just as capable, if not more capable, of rendering a whole area unhabitable.

[@abhijeetvasishtha4627]

In KALPAKKAM(INDIA) we are also working on thorium based power plant.

[@PaulHigginbothamSr]

abhijeet---yes but the wrong damn type, not molten salt but just like now.

[@johnsmith1474]

You ought to be working on toilets, air pollution, dirt, disease, and birth control.

[@deepankarroy774]

@@johnsmith1474 none of the country is perfect. What matter is how we dedicate ourself to solve this problem. I hope when you go to school next time you would have fun

[@johnsmith1474]

@@deepankarroy774 - Translation: Still shits outside. You are blocked, just like India's national sanity.

[@adityaverma6754]

@@johnsmith1474 atleast we know our problems u suckers need to wear bulletproof vests to survive day to day school .

[@robjeanbras1130]

I can't wait until we each get our own personal reactors so I can say "Luke, I'm shutting the power down."

[@genildomiranda1690]

Yep my son will be called Luke, getting to say that, and "I'm your father" does it for me

[@PaulBrown-uj5le]

Lol, my son is already Luke so I just need the reactor!.

[@SHREDTILLDEAD]

That will never happen, unless it is based on specific methods. Everybody gets ants in their pants when they think about these new methods ,but never ask if they should. The real question is how much raw uranium , and thorium are you going to need. We cannot keep taking it out of the ground and not worry about decreasing the population.

[@tomfly3155]

Apparently he never said "luke, I am your father". He said "no, I am your father". Mandela Effect bit@#es

[@nagarjunkashyap5987]

Luke?........More like Nuke

[@spacehabitats]

The LFTR doesn't just make a Fukushima or Chernobyl type accident less likely, it makes it impossible. You can't have a meltdown since the fuel is already liquid. Since the molten salt "freezes' at room temperature you could set off a bomb in the reactor and the scattered salt would end up as solid pellets on the ground instead of leeching into the water table. Without a pressurized water cooling system you don't run the risk of a HYDROGEN explosion when an out of control uranium reactor splits the H2O into its component elements as happened at Fukushima. Although you CAN make a bomb out of U-233, it is less stable and trickier to use. Would be terrorists or even rogue nations would be far more likely to blow themselves up and would have a much harder time maintaining nuclear arsenal. And if you were really concerned about proliferation, there are designs for MSR thorium reactors that are modular, completely self contained, and tamper proof. They are actually easier to build but lack the ability to breed new fuel so they lack the efficiency you mentioned. But since they are still as efficient as uranium PWR's and infinitely safer, they are a much better energy solution. Thorium isn't just more plentiful than uranium, it would be essentially free since it is currently mined and discarded during rare earth metal mining. In fact, using thorium would eliminate one of the biggest problems facing rare earth mines in the U.S.A., getting rid of thorium which must be handled nuclear waste.

[@lifuranph.d.9440]

Great comment, John. I guess China can do without me. HaHa!

[@metallkopf988]

the instability of U²³³ makes it a royal PITA to work with. Rogue states may manage to make a workable bomb from that, but terrorists probably won't. Unless the goal is making a "dirty" bomb with conventional explosives and radioactive material. Even so, they'd more easily steal radioactive components from medical x-ray devices instead of bothering with U²³³. Besides, to handle any kind of radioactive material without proper training is a very stupid idea.

[@bluesky6985]

They chose uranium so they would have nuclear proliferation and a cold war which was a scam

[@lifuranph.d.9440]

@@bluesky6985 Exactly Correct.

[@metallkopf988]

**Tinfoil hat is burning**

[@pgpimages]

The story of the volunteers is actual an urban legend. I have been studying Chernobyl for over a decade and have spent over 100 days in the zone and also produced and hosted a show on discovery channel about Chernobyl I for the longest time heard and believed this story. It was on my last visit that I got to speak with many operators that worked at the plant and those who worked as part of the clean up. The volunteers never volunteered and in fact 2 of the 3 who were identified as the volunteers are actually still alive (the 3rd died a few years ago from a heart attack)

[@ilovecops5499]

Thanks for the confirmation. I always suspected it was a scam.

[@ilovecops5499]

It was a Urban Legend to glorify the Communists.

[@mayoite160]

so did they actually go down there or was that a fabrication too?

[@GEOHHADDAD]

Watch a documentary called Chernobyl Heart. The heroism of those that fought the containment battle was noteworthy. The long term harms have been substantial and the lessons barely learned. Separating fact from fiction about nuclear accidents is difficult because the knowledge of physics and environmental science required to separate nonsense from science is more than just formidable. Most people with pretty good lay level, but formal, backgrounds in physical and biological sciences, myself included, still rely on the opinions of others. Because of the extreme risks posed by ionizing radiation, the overarching doom of nuclear war and the general difficulty of the subject matter most people are easy to mislead based on their preconceptions, politics and general predisposition or lack thereof to rely on conspiratorial thinking or (at the other end of the spectrum) over reliance on authority consensus

[@alexharner6057]

What you say seems to be in contraction with this: Discovery Channel - The Battle of Chernobyl (2006). Please clarify.

[@AshGreen359]

Gets to Thorium at 6:20

[@Winterx69]

Amen!

[@generalking9029]

Jesus he sure rambles on

[@palomarjack7090]

But global warming right off the bat. And, even gets the purpose of a moderator in a nuclear reactor completely wrong.

[@gabrielp9646]

@@palomarjack7090 Please, tell me what globan warming is, or how would you define it.

[@clottedcreamtea8695]

@@gabrielp9646 get a globe and warm it 👍 Not sure about snow globes ,or plastic ones 🧐

[@DaveKeil]

A few points that in your explanation are a little vague: Love your channel. 9:23 - You don't have to "worry" about it running away because all the reactions occur in the liquid phase in the molten salt, and if it overheats and runs away you can dump it into a freeze tray. 10:35 - Higher temperatures mean higher pressures within the steam loop (Which is kinda like 'more steam' but unclear) which means an overall higher efficiency of the generator. (See Carnot's work) 14:40 - No no. No. Noooo. No. A refrigerators working fluid is usually HFC-134a. Same Freon most cars use. Using air would be way less efficient.

[@pjeaton58]

Refrigeration now uses cyclopentane ?

[@DaveKeil]

@@pjeaton58 yeah, I've seen a few. They exist. The working fluid defines the pressures that the unit runs at for hot and cold temperatures.

[@TonyNalagan]

The coils on the back of the refrigerator (condenser coils) does not contain pressurized air. It's pressurized refrigerant (usually R-134) that has been cooled to a pressurized liquid. It becomes a lower pressurized liquid when it is circulated into the evaporator coils located in the freezer section of the appliance where it absorbs heat in the freezer section of the appliance and becomes a lower pressurized gas (because it undergoes a state of change).

[@damonsisk4270]

You are so correct. Sad so many people depend on refrigeration and have no clue how it works. Perhaps his claim that compressed air exists inside the coils was not such a 'Brilliant' claim...

[@JoshuaTootell]

People really don't need to know how refrigeration works. Anything beyond whatever chemistry class they took in high school or college is fine ​@@damonsisk4270

[@damonsisk4270]

@@JoshuaTootell I disagree. We are a society highly dependent on technology but in the population, the average understanding of even the most basic principles is very low. Some ideas for improving the systems we have built (upon which our life depends, such as electricity) are just silly once a basic understanding of physics is attained. When the general population is ignorant of these basic facts, poor ideas will be supported by that population (through voting and perhaps investment) and will retard advancement in the best case but result in catastrophic loss in the worst case.

[@Mukation]

Great video, Joe! But fridges don't use "air". They use different refrigerant fluids that are in gasform at atmospheric pressuare and that tend to vapourise at temperatures below zero. Like Isobutane etc.

[@AlexandreMoleiro]

Yep, they use a closed circuit. Just like an AC unit.

[@0409hdl]

Yes, using air will just freeze up the pipes. The refrigerant gas has to be extremely dry to prevent this.

[@GreenspudTrades]

lol not a good endorsement for Brilliant

[@AzzA-68]

Fridge uses air = zero credibility

[@fr8fr6dr69]

Me before KZbin: "Gawd, I wish I could know everything." Me after KZbin: "So, yeah, the thing on the end of the shoelaces is called the aglet."

[@metalgear541]

fr8fr6dr damn. Now I know that. Thanks lol

[@Streamtronics]

Did you learn that from Chris Boden by any chance ;D

[@oscargoldman85]

The area on the back of a mammal that it cannot reach to scratch is called the "anetsis".

[@oscargoldman85]

@Ben Louis Thats only correct when you have two laces twisted together. ;) On a separate note, RNA Telemorase were demonstrated by Watson(of Crick & Watson) to Alan Turing as being a multi state enzyme that could change state, depending on what it arbitrarily read on the DNA chain, moving up and down the chain, and performing changes as instructed; it is effectively a biological Turing machine. READ THAT LAST LINE AGAIN, IT SHOULD BLOW YOUR MIND. Also - they reverse aging, but that's a whole other thing.

[@twilight814]

I learned that telomeres were on the end of a strain of DNA on KZbin... .true story

[@URProductions]

14:25 Sorry sir, you are wrong. Those coils at the back of your fridge are *not* air, they are tubes full of _refrigerant_ , a chemical (often a hydrofluorcarbon) with a very low Evaporation Temperature (like -20 or -40 degrees C). The _air_ is passing through the vents that are in between the coils, blown out from inside the fridge by a fan or fans located right behind those vents. Your fridge isn't cooled by air at all - it's cooled by the _refrigerant_ . After the _Condensing_ _Coils_ (which are the coils we see in the picture you showed us), the liquid refrigerant passes through what's called the _King_ _Valve_ , which allows only a small trickle of liquid through into a Low Pressure section on the other side. Because a liquid's Boiling Point increases with pressure (and vice versa), and because of the Refrigerant's low boiling point, the Liquid Refrigerant winds up "flashing" into vapour. And because it takes energy for a liquid to transform into a vapor, heat is stolen from the surrounding air as the Refrigerant evaporates while through another series of coils - the _Evaporator_ _Coils_ . THIS is what makes your fridge cold. After this, the now gaseous Refrigerant is pumped out of the _Evaporator_ _Coils_ by a small pump simply called the _Compressor_ , which compresses the gas back into liquid and back into the _Condensing_ _Coils_ that we saw in your image. Air from the inside of the fridge is blown out through those vents we see in the image by small fans. This prevents there being stagnant air inside fridge which would slowly heat up to ambient temperature due to Thermal Equilibrium. I mean, c'mon man. I hope Brilliant.org doesn't pull their ad revenue for making them look stupid.

[@GEOHHADDAD]

I caught that too. Was thinking...wow....where do I get one!

[@kb9oak749]

@Stephen Bennett He could have found that out instead of assuming.

[@Biocrittas]

The reason that people say you can’t weaponise products from the lftr is that while one could remove the u233 from the reactor which can make a bomb, as you mentioned it would be unavoidably contaminated with u232. The gamma radiation resulting from the u232’s decay chain make it impractical to use that contaminated u233 in a bomb as it would be very hard to shield and therefore have a detrimental effect on the bomb itself and anyone who was near it while it was being assembled, stored and deployed.

[@b43xoit]

Also acts as a beacon.

[@NeverTalkToCops1]

+Biocrittas Any and all fission/fusion or combinations thereof, using everything possible from the table of elements, has been done, on paper, or in an actual device. At least one U233 bomb was fashioned. It was a flop.

[@benhayfield6182]

Also its worth noting just how much safer liquid salt reactors can be. Current plants use external power to suppress the reaction so a loss off power is a huge problem. Liquid salt plants use external power to sustain the reaction and so are shut down in the event of power loss. Your protected not by safeguards backups and alarms but by physics. Also I believe the hard gamma problem is also a problem with weponising it as it makes it more dangerous to work with and much harder to do covertly as it is hard to hide the gamma from satellites.

[@thamesmud]

The boffins at Oak Ridge used to turn it off on Friday afternoon and start it up again Monday morning !

[@Turbofab]

Can we just take a moment to appreciate Jo and the amount of work involved in bringing us this content and being able to make it digestible, Big respect for you Jo

[@petersurdo4984]

Nice job. Learned a lot. Thanks.

[@devoutapostate9005]

The Oak Ridge Boys, nice.

[@joescott]

I was waiting for someone to catch that. :)

[@basic48]

I am researching just this subject at Cambridge. My project report will be published at the end of this year. Safe Nuclear Power is the solution to Climate Change. We need 30,000 new reactors if we are going to balance fossil fuel use. Currently, it takes 20 years to build and license one...we need to accelerate this process immensely. Support safe Nuclear Power.

[@vax20051]

I totally agree. The technical challenges can be overcome. The social & political challenges associated with building the reactors need to be addressed. I'm glad Joe is putting out there a great video explaining the technology. People need to be educated so they do not fear nuclear technology. I think this could be the safest and most practical solution to the energy crisis.

[@sinephase]

One of the guys saved some of the piping from the experiment, so it would be interesting to get an account of how much actual "corrosion" happens. He said the pipes were fine after over 8000 hours of run time.

[@ayapotato7429]

Do you think that solar, wind and other renewable sources won't make nuclear energy obsolete in the near-ish future? I totally understand the idea that nuclear is a better energy source than fossil fuel, and of course there are applications (and entire regions) where renewable energy isn't going to cut it (extreme North and South, remote isolated bases and outposts, etc.). But 30 000 reactors, you are talking about the mass energy production here, like replacing coal power plants with nuclear reactors, no? It feels like replacing these with renewable energy production would be a better way to go.

[@vax20051]

Solar and wind are not energy dense enough to make nuclear power obsolete IMO. But, we don't have to pick just one renewable energy production method. We can invest in all green energy wind solar, thorium power. The ultimate goal is to eliminate fossil fuel dependency.

[@vax20051]

That would be interesting. It's defiantly not an insurmountable problem.

[@mrkokolore6187]

I'm glad you mentioned the MSRE.

[@ethanharvest4917]

I love how you put the title of this episode not only on the screen but read off the names of everyone who actually literally asked you to do this episode because it’s so unbelievable that people specifically requested this tailored version of an episode and you tell her to them! So bravo LOL

[@LawtonDigital]

Back in the '80s there was a PWR video game that let the player control the rods, pumps, and valves. Periodically, random stuff would break, and you'd have to figure out from the various pressure/temperature readings what went wrong. You could then expend a limited number of maintenance workers to go fix what you think broke. Good management training, that.

[@MisterLepton]

Robert Lawton woah, this should be recreated for mobile. I’d buy it.

[@Datan0de]

Robert Lawton I think I played this game in the early 90s! I had no documentation at all and only a vague understanding of reactor operation, so I typically ruined everything in a matter of seconds.

[@WimWoittiez]

Would love to know the title of the game. Do you remember?

[@johnwang9914]

The Oakridge reactor was an Uranium 235 reactor not a Thorium reactor but it did test the basis of a molten salt reactor which would be the fissile core of a Thorium breeder reactor. It was the canceled "breeder" program that was to test using Thorium as the feedstock. Also, water was never or ever intended to be turned to steam in these molten salt reactors as the temperatures of the molten salt would require extreme pressures with the steam produced. The reactor of Oakridge was intended to be used as a jet engine for the US airforce so either air would be passed through the reactor (the direct cycle design) or an intermediary heat transfer medium be passed through to then heat the air in a heat exchanger (the indirect cycle design). The civilian power version was intended to use a gas as the heat medium and drive a Brayton cycle turbine which are both lighter and far more efficient than steam turbines. Now, the Thorium slow breeder reactor was in competition for government funding with the fast breeder liquid metal reactors which bred plutonium from uranium 238. There is an audio tape of Nixon discussing choosing the fast breeder over the slow breeder because the fast breeder provided jobs. A liquid metal fast breeder reactor is inherently dangerous and requires a staff of hundreds to keep safe while a Thorium slow breeder would be self regulating and need little more than a security guard.

[@johnwang9914]

+Isaac Fahrenheit A Thorium reactor is a breeder reactor. Thorium 232 itself is not fissile, it can not form a chain reaction and cannot be used to produce power in a nuclear reactor but when exposed to thermal neutrons (slow neutrons), it transforms into Thorium 233 which decays to Protactinum 233 which over 30 days decays into Uranium 233 which is fissile and can be used to produce energy. The fast breeder reactor exposes the non-fissile Uranium 238 which is more plentiful than the fissile Uranium 235 to fast neutrons and transmutes the Uranium 238 eventually to fissile Plutonium 239 which can be used in a reactor to release energy in a chain reaction. Note that the probability of a fast neutron collision is very low but a fast neutron collision with Uranium 238 has a high probability of producing Plutonium 239, conversely, a slow neutron bombardment of Thorium probability is high but the probability of eventually producing Uranium 233 though high are not quite as high as with the transmutation of Uranium 238 to Plutonium 239 though it is still very likely. In a Thorium reactor, a Uranium 233 core produces the energy and neutron bombardments to the Thorium, the Protactinum is constantly extracted and stored for thirty days before being re-introduced as the Uranium 233 in the core. One design has the Thorium in a blanket, another has the Thorium mixed in with the Uranium. Note proponents of the fast breeder concept often cite the higher efficiency of the transmutation but the low probability of the fast neutron collision in the first place results in less than 1% of the Uranium 238 becoming Plutonium in a conventional nuclear reactor. Breeder reactors breeds their fuel from non-fissile feedstock. The downside of breeder reactors is that some fissile material is needed as a seed to start the process. Of course, such material could be tapped from existing reactors hence the growth rate is exponential but even using the fissile material in our nuclear warheads, we would not be able to produce enough Thorium reactors to keep up with forecasted exponential demand for energy. Thorium reactors can be part of a solution for clean safe energy but it can't be the only solution.

[@johnmasursky7717]

​@Isaac Fahrenheit a breeder is ANY reactor that takes fertile (non fissionable) material and turns it into fissionable (fissile) material and subsequently fissions this secondary material to release the energy that will be harvested. A Thorium Molten Salt Reactor is just one type of numerous breeder reactor scenarios; in it Thorium 232(which is fertile) is converted into Uranium 233(which is fissionable).

[@grande521]

I got this channel suggestion from watching the every day astronaut, and man I am definitely not disappointed, great channel, great content SUBSCRIBED!

[@Matthews_Media]

Thanks for the great content!

[@andrewpienaar4522]

It is Not Air in the tubes of a fridge, as the pressure to condensate (turn to liquid) these gasses are way to high for the system to withstand. Previously it was CFC gasses that are known for destroying the Ozone in the atmosphere. For compatibility, they have been swapped out with HCFC gasses that can run in the old systems. New fridges are designed around HFC gasses that run at different pressures but have no impact on the Ozone. Fridges work on the principle of swapping out heat in two cycles. The Liquid cycle going into the fridge and the gas cycle coming out of the fridge and into the outside radiator. Compressing and expanding the gas / liquid changes the heat energy state through the "latent heat coefficient" as to allow the system to reduce the overall heat inside the fridge.

[@LarsPallesen]

Thank you. That was a really great explanation.

[@ChrisWilson999]

A superb summary of what it takes Kirk Sorensen 2.5 hours to cover. A few errors here and there on this subject would be impossible to avoid for the vast majority of people without a PhD in nuclear engineering or some other technical field. Don't sweat the haters who couldn't make a video with a million views to save their lives. One of the reasons I like your videos so much is that I get to see an intelligent person's take on many highly technical and awesome subjects. For anything you miss, it's more than made up for by your great presentations. Thanks for bringing more exposure to what could be the future of power generation.

[@nooneinparticular9868]

I like your content. Thanks man. Keep posting.

[@shdwshard]

Dude... you need to screen your scripts. I'm no expert on nuclear power and thorium, but you got MANY things wrong, down to the level of sheer laziness. * Moderators don't absorb neutrons, they slow them down. Fast neutrons are what are emitted by fissioning atoms, but they are moving... REALLY FAST, and that's not always what we want, because thermal (think: slow) neutrons are more readily absorbed. Both types are usable, but the reactor designs (and necessary amounts of fuel) are very different. * The graphite core of a LFTR isn't a neutron emitter, it's a neutron moderator much like water is in a PWR or BWR. Fast neutrons aren't absorbed as easily as thermal neutrons, so when the salt is removed from the core, it looses the ability to continue the chain reaction due to the lack of moderation (The neutrons speed off out of the salt mix, the neutron economy drops below 1 and the reaction ceases) * U232 absolutely can be used as a bomb fuel, if you can isolate it. The issue with U233 as a fuel for a bomb IS U232. The hard gamma emissions mean the bomb would need INSANE shielding to avoid frying the detonation circuitry, or else it might just blow up randomly. (Not a desirable property for any weapon) This is why proponents of LFTR claim it can't be used for nuclear weapons, and many will champion U232 as a benefit, not a down-side, due to it making proliferation significantly harder. * PWR and BWR are very different beasts, not just because of the lack of the secondary coolant loop. The primary loop being pressurized means there are no steam bubbles passing the nuclear fuel, making the primary reaction much more stable. Remember, the water is also a moderator, so the water staying a liquid is actually desirable to maintaining a stable neutron economy, and hence a safer reactor, since fewer neutrons are lost, hence fewer excess neutrons are needed. They also typically have several secondary loops, making servicing of the turbines possible without shutting the whole reactor down, and the total isolation between the primary and secondary loops mean the steam turbines aren't circulating radioactive water. (Neutron bombardment in the core will make MOST materials, including water, radioactive eventually) This means it's possible for humans to work in the turbine building, so the difference isn't trivial. PWRs are newer, and considerably safer than BWRs, and it's worth giving that a few extra seconds. * The difference in temperature of LFTR, pebble bed reactors, etc, as compared with water moderated reactors isn't just the amount of water they can boil, it changes fundamentally what you can do with the reactor. Pebble Bed reactors can heat the water hot enough to disassociate the atoms, so you can directly extract hydrogen and oxygen for all sorts of uses. The excess heat can also be used as the pressure source for water desalination, and after all that, you can still generate steam for running turbine generators. LFTR's dream combination is supercritical CO2 turbines, which are smaller, lighter, and vastly more efficient than bulky steam turbines. It isn't even possible to run these turbines if you're talking about water cooled reactors because the water moderator limits how hot they can run. (The physics of pressurized hot water and limits of our material engineering abilities mainly) * Fissile vs Fertile isn't about absorption vs fission. All atoms can in theory do both, and the percentage they do of each is important to the neutron economy of the reaction. Fertile fuels are fuels that can be made fissile through a single neutron absorption. This includes Thorium, and U238 because a single neutron absorption by each will result (eventually) in a fissile material being produced. The term "breeder reactor" refers to this property as well. The breeding is the conversion of fertile to fissile fuel. There's a reason why one neutron is important. A typical fission will emit 2~3 neutrons, typically in the 2.5 range. You need 1 neutron to continue to the chain reaction, leaving 1.5 to do something interesting with. 1 absorption to generate more fissile fuel is therefor permissible, leaving 0.5 neutrons (on average) for other losses in the system. So a fertile fuel can (in theory) continue a nuclear chain reaction, it's just not possible to start a chain reaction with only fertile fuel. * Trans Uranics are a side product of nuclear reactions that occurs when fissile or fertile fuels continue to absorb neutrons without fissioning, but they're far from the only thing in the waste stream. Fission by-products are the remnants of the split atoms, and are typically neutron heavy for their (now smaller) size, compared with the original uranium or plutonium atoms which were relatively stable. The third part of the fission stream is the unspent fuel. This witches brew is the problem. Fission by-products are typically very hot, and decay pretty quickly. (hundreds of years) Trans-uranics can be longer lived, but are also typically pretty hot. (thousands of years) Having the uranium or plutonium mixed in is problematic however, because it continues to decay, (millions of years!!!!) leading to continued production of the shorter lived, much more radioactive by-products, even though the fissile fuel itself isn't that hot radiologically. The main advantage of LFTR is that because the fuel is a fluid, all three of these streams are separable in-situ, AND, because you're starting with relatively light elements, the production of trans-uranics is much lower, (takes several more neutron absorptions) so the majority of the waste stream is shorter lived, almost human timescale waste. * The LFTR freeze plug isn't about the core getting "too hot" per-say, but instead about the reactor failing passively. If the reactor looses all power, the freeze plug stops being cooled, whether by a fan, heat pump, etc. The plug melts, and removes the fuel from the core, which removes moderation of the fuel, stopping the chain reaction. The freeze plug leads to a drain tank which is engineered to maximize passive heat rejection, as the fission by-products are still decaying and producing heat, but, as the fuel is already a liquid, it will flow into whatever shape is needed. * The material degradation myth continues to pop up, but the MSRE DID NOT HAVE THIS PROBLEM! Dissolution of metals into the salts, and varying solubility over the temperature range of the heat exchanger is a known issue, but never presented a problem because it's expected and engineered for. MSRE did have an issue with Lithium fissioning into Tritium, and this process is actually used in thermonuclear weapons to generate hydrogen in-situ for fusion, but it's widely believed that better isotopic separation of the lithium isotopes can alleviate much of this problem, as only one of the two common isotopes decays easily under neutron bombardment. * One of the big advantages of a LFTR that you didn't touch on is the ability to extract useful radio-isotopes. NASA would really love a new supply of Plutonium 238 for space probes example, and there are lots of other useful isotopes for medical, commercial and scientific purposes. * It's not Filbe Energy, but Flibe Energy. The acronym comes from the contents of the molten salt. (F)loride, (Li)thium, (Be)rrilium salt. * Refrigerator coils DO NOT CONTAIN AIR! What they contain is way cooler actually, as the working fluid turns to a liquid when compressed a bit above atmospheric pressure, and vaporizes again when that pressure is released. It's a volatile (easy to vaporize) fluid that absorbs and releases heat as a result of both the phase and density change from going from a gas to a liquid. The total heat content of the working fluid is the same in the liquid or gas phase (minus the heat of vaporization) but as a liquid it's WAY MORE DENSE, so that same heat volume means a larger temperature. Yes, I know that's a HUGE amount of material, but that's how much this video got wrong! Please run your scripts by someone!

[@FonsecaStatter]

Thanks for your clarifications... I confess I was getting puzzled and confused, specially with some of the comments

[@kingmooseify]

Charles Chappell i

[@sergiokorochinsky49]

Charles Chappell Your post has almost as many error as the video, but I am glad somebody tried to put some order in the chaos. The few half-truths in the video are lost in all the garbage and errors. Talking about LFTR instead of MSR in general, and naming Sorensen instead of the creator of this concept (former director of ORNL) is an insult and a disgrace. This video is yet another repeat of Sorensen's misleading propaganda. Every nuclear engineering student falls in love with MSRs, and that love lasts, on average, two and a half hours (that's the time you need to see all the impossible-to-solve engineering problems).

[@xenoidaltu601]

Charles Chappell You should make videos too! :D

[@domsau2]

Sorry: thumb down for the video. Bravo, Charles Chappell.

[@dojokonojo]

Someone from a thorium energy start up came to give a guest lecture on thorium reactors in my engineering class back in 2010, and the young impressionable freshman that I was thought 'Hey, this is really cool! I can't wait to see operational plants!' 8 years later I'm still waiting lol.

[@joshuarichardson6529]

Since you need 20 feet of concrete to contain the nuclear vessel and it's radiation, it's not cheap to build. It's just the fuel that's inexpensive to acquire. Then there's the question of where you're going to bury the nuclear reactor that won't have people going "not in my backyard".

[@baronvonlimbourgh1716]

@@joshuarichardson6529 you really need to do some more research.

[@ididit9026]

I love your intros, this is just amazing way to introduce a topic like that!

[@michaelmyrick6973]

always learn something new bro thanks for all ur work

[@vipondiu]

Very good explanation of the thorium cycle, Joe. Just for clarification, the breeding of U233 unavoidably breeds some U232, that as you said, decays into Tl208 which renders the U233 basically useless for weapons. It is a great nuclear poison, hurting the neutronics of a nuclear pit core, besides making the handling of the fuel much more difficult and frying tightly-packed electronics inside the nuke with gamma radiation. Still, not impossible to build a bomb out of it, but at some point it is more practical to use another fuel as U235 or Pu239, that's why they discarded the thorium cycle during and after the Manhattan project. As far as I know, there's no way to breed U233 without a minimum amount of U232. To anybody wanting to learn more on LFTR, look for videos on youtube of any talk of Mr Sorenson. Thanks Joe!

[@marksmith8079]

But so bad a chance to make bombs that no country has even tried.

[@JonathanSchattke]

This is new you heard wrong. The reason Plutonium is preferred over U233 is the alpha-delta solid phase shift allows easy implosion devices, and no such physics exist for Uranium.

[@jhonfamo8412]

This is new Sorenson the man

[@meneldal]

You don't have to use Pu239 for bombs though, it works great as a fuel. I think the video was dishonest because breeder reactors work and can use U238 completely (by turning it into Pu).

[@Clean97gti]

He skipped over a couple important points. 1. The U233 you're making is screamingly radioactive, which makes it hard to handle. Much harder than Pu. 2. Using a power reactor to make bombs means you get dirty bombs, not fission bombs. Sure, you could get enough fissile material at the needed concentrations eventually, but it's nowhere near economical enough. It would be like taking crude oil, converting it into diesel, then burning it in a really dirty motor, collecting the unburned hydrocarbons in a special filter and reprocessing then into fuel for a passenger car. Much easier to build the refinery and isolate the fuels you want from the beginning.

[@markkim7348]

Thor, the god of Thunder is going to give us power Neat

[@jackalope839]

Isn't he the god of punching things?

[@figbender3910]

He punches things with his hammer

[@Baylin99]

In a hamster wheel XD

[@markkim7348]

On second thoughts, I think he's the god of hammer

[@wsmith49]

Thursday is named after Thor (Jupiter's day in Romance languages, e.g., "Jeudi" in French (kinda cognate with "Jove"). Mjolnir (say: Myahl-neer) is Thor's Hammer; when he throws it we have lightning followed by Thor's THUNDER! Norse gods are cool; they emit their own brand of radioactivity that, who knows, might someday lead us likewise to Ragnarok. Sorry, I'm way off topic. Fantastic video! Best explanation I've heard to date for the thorium fuel cycle. Even though doddering old fools like myself don't deserve it, please keep these entertainingly informative videos coming!

[@oliversimpson2602]

Thanks Joe. Really interesting video

[@asevado]

1:22 those 3 men survived and 2 of them are still alive , 30+ years later.

[@scottl8973]

I am glad you did a video on this. I was not sure how viable thorium really was even though my research turned up almost the same stuff. I just have a hard time sifting the crap from gold. And sorry if you already have a lot of corrections on this but refrigerant is not air. The stuff in the coils, it’s either freon or something close to it. I really do love the videos so thank you.

[@claymccormick1203]

technically thorium is the most viable of all the options politicals not so much.light water and fusion have huge investments the investors do not want a redheaded stepchild to walk away with the prize.

[@jhonfamo8412]

Scott Lashlee ammonia..?

[@theCodyReeder]

Hold up. Brilliant told you that the fridge compresses air?! Well now I'm glad I didn't take their sponsorship! Lol 😆

[@twirlipofthemists3201]

Air, gas, potato potahto... But you're right.

[@blindbrick]

I was Just about to comment about that. But air could work, just higher pressures. I hope Your channel is OK. I love all Your stuff Cody. I hope to see some mining soon, if KZbin allows it.

[@MajSolo]

thumbs up for the joke

[@PaleGhost69]

Well, technically wouldn't cooling room temperature air to food safe levels compress it. Barely measurable of course but it would.

[@bigredinfinity3126]

air is made up of different gases so all have different freezing points and behave differently

[@82spiders]

Very well researched and presented.

[@cutterXXX123]

Thank you! Molten salt thorium reactors I've been sitting on the back burner way too long.

[@FedericoGalimbertiApparel]

Joe, I have been following the technology on MSR for two years and I must say what you managed to explain in these few minutes of your clip is really fantastic as it’s concise, clear and easy for a non-tech nerd to grasp it. Sure, if one is interested there’s much reading to do if you want to become knowledgeable but your video has done an amazing job to kick start that process! Congratulations!!

[@joescott]

Whew! I'm glad you think so. This one was a major challenge (hence how late it was getting out today).

[@baloog8]

Like to point out a subtle detail few know about. U233 is detonatable but tends to predetonate and fizzle because of its high neutron emissions. So it is low yield and dirty even when in implosion form which by the way is extremely tough for amateurs to achieve the precision in hydrodynamics. It can be boosted by plutonium but is still just a waste. Terrorists trying gun type will get nothing but pretty much a dirty bomb only.

[@propelegant]

Alvin M. Weinberg is the unsung hero of this story. he led the team that designed the Light Water Reactor (LWR) for use in submarines.which proved to be successful. However Alvin did not recommend LWR for use in the production of electricity for the grid because it would not scale up without an inherent increase in safety risks. He proposed the use ot the Liquid Fuel Thorium Reactors (LFTR) which was originally designed to power high flying bombers for the airforce. In the end, Nixon favoured a rival fast reactor technology based in California which would attract more votes. LFTR has many additional advantages. There is very little waste produced, in fact, old LWR waste can be burnt in these reactors. The safety plug works by cooling an escape pipe with a fan to freeze the molten salt. when there is a loss of power the fan stops and the plug melts. the molten salt drains to another tank where there is no moderator and the reaction stops. Even if the reactor leaks the salt just freezes solid almost self-healing. The gamma spike can be used as a safety feature as any attempt to break into reactor would be observable from satellite and seriously injure or kill the thief. There is a variety of useful byproducts including vital isotopes for medicine, space, and excess heat can be used for desalination. I could go on but I am no expert just puzzled by the lack of government interest. One idea put forward is that LWR suppliers make money from the costly uranium pellets (why change?) as with ink cartridges for printers?

[@chipfriday8166]

Just follow the money..... it's not that hard.

[@patricksarama4963]

“Nuclear power is one hell of a way to boil water” -Albert Einstein

[@samann95014]

Einstein didn't had all the right answers.

[@sheiladawg1664]

It's the energy density. Nuclear plants are refueled every 1 1/2 to 2 *years.*

[@justincook4083]

Just found this channel ,interesting stuff to jam out to while at work. I sub'd

[@Locut0s]

I LOVE your channel Joe. One thing I wanted to mention however about the beginning of your video. Almost everything you described is accurate. The Chernobyl disaster was fucking terrifying but the number of people who actually died as a direct result of the radiation from the disaster in the ensuing weeks is actually fairly low, likely in the range of 30 to 40 from what I can see. Now of course the number who died in years to come is much higher but also much harder to quantify due to how cancer and statistics work.

[@MonMalthias]

Assuming linear no threshold holds, up to 3000-4000 extra deaths from cancer (mostly thyroid, and assuming those are left untreated) will occur. (7000 people received doses sufficient to induce thyroid cancer, with an assumption of approximately 40% or so that those people will die) In reality this has not eventuated. It is likely that the _total_ death toll, including latent deaths from cancer, will not exceed 100 people. Deaths from radiation sickness and burns total at 53. Any increase in cancer incidence, even assuming LNT multiplications of man-Sieverts, will not result in increases in cancer detectable by even huge studies with massive statistical power. The increase is something like tens of thousands of excess cancers against a background of hundreds of millions of annual cancer incidence from all causes. www.unscear.org/docs/reports/2008/11-80076_Report_2008_Annex_D.pdf " The models pre-dicted that by 2065, about 16,000 (95% CI: 3,400, 72,000) cases of thyroid cancer and 25,000 (95% CI: 11,000, 59,000) cases of other cancers could occur owing to radia-tion exposure resulting from the accident, whereas several hundred million cancer cases would be expected from other causes. It is very unlikely that this additional cancer burden due to the largest nuclear accident to date could be detected by monitoring national cancer statistics." What _is_ detectable is a measurable increase in thyroid cancer. As far as cancers go, it is highly treatable and relatively easily diagnosed even without extensive medical facilities. Ironically the thyroid cancer caused by radio-iodine is treated with...radio-iodine. A massive dose of radioactive iodine will kill off cancer cells mutated by low levels of radio-iodine exposure. It is as Paracelsus says - the dose makes the poison. The alternative is thyroid resection. Either way, the worst nuclear accident to date will kill _less people across the decades its influence will be felt_ than the annual death toll from _being struck by lightning._ Even assuming that _every single one of those 7000 excess thyroid cancers results in death._ Even assuming that the mathematical predictions of 16000 cancers holds. en.wikipedia.org/wiki/Lightning_strike

[@paulbedichek2679]

I thought Chernobyl would have killed 20 to 30 million I know nuclear power has ways been our safest energy even without considering global warming, but it was amazing that even though th russians did everything wrong from design operations and not building a containment building radioactivity from th accident killed almost no one,th cancers it caused have 99% recovery and take a long time to kill you,ebvery sings day coal kills many times more in a few hours than nuclear has in history, future reactors will be much safer.

[@papagrounds]

100k is close! :) Keep up the good work, Joe! 👏

[@Muuip]

Great concise presentation! 👍

[@RalphDratman]

This is excellent. Thanks, Joe.

[@olafurgardarsson1780]

One of the best videos you have done Joe

[@josephgeis6641]

My Thought is give Thorium a try better than what we have now.

[@ElishaBentzi]

The problem with thorium and nuclear power is that can destroy the business of gas, and this will destroy the financial markets. The thunders produce radiation, radiation was never a problem, just the dangerous radiation initial wave, all the life thrive with high radiation.

[@Clean97gti]

The biggest reason we don't bother with Thorium is that Uranium is still readily available. Why go through the extra transmutation step to make Thorium into U-233, when you can just get natural Uranium and enrich it as needed.

[@JN-dl9fi]

@Mike McKleen Thorium is natural and we got an abundant quantity of this material, it's been 4 years out of 5 that they are making a test to replace uranium by the thorium in the actual nuclear plants 2.5 years per tests, the first is a sucess generating as much power as the uranium does and with the advantages of much much much less radioactive waste. Futhermore, if politicians could make up their minds, an equal power generation using Thorium is estimated to be replaced every 20 years, instead of uranium which has to be replaced "every less" than a year. The real biggest problem right now is as Elisha's saying, but there's also the people that are frightened, remember Fukushima and Tchernobyl.

[@baronvonlimbourgh1716]

China is on it. They are not bogged down by energy conglomerates.

[@mikevlek]

“Destroying the waterpumps and sendingthe other reactors into overdrive and also melting down”. The last reactor closed in 2000 and the other 2 a few years earlier, those never had any problems, they even kept going while all of the liquidators and other people. Wheredying aroumd the plant

[@jonathanpratt56]

Thank you for doing this video. I have been putting this information for about out 8 years and not at your level. Trying to give motivation to young people to pick up the Nuclear power idea and get involved with clean power production.

[@user-bm8uw8oj4k]

What will/can you do with hundreds of millions of " clean " Curies in the average reactor? 1 curie = 1 gr. of radium

[@macbuff81]

I learned a lot here

[@ugn669]

The "500 kilometer" evacuation zone thing isn't true. I mean that would require evacuating most of Belarus and Ukraine, parts of Russia, Lithuania, Moldova, Poland, Latvia... as far as Romania! No.

[@TheFrontyer]

The exclusion zone was anout 2600km^2. Lots of belarus was abandoned, and still is today, even though many people refused to leave. Even in Norway we had to kill farm animals (especially raindeer) because they were contaminated and could not be used for food.

[@Krusador42]

@@TheFrontyer area of exclusion zone = 2600km^2 => radius of exclusion zone = 29 km

[@nicolarivarossa4027]

very clear explanation

[@derrick211000]

Love it great video, science, comedy, just great! Liked and subscribed.

[@russell2449]

I heard about these over 10 years ago and I thought this was a slam dunk, but a decade later NOT A SINGLE thorium salt reactor is slated to be built, wtf???

[@baronvonlimbourgh1716]

There are loads of experimental ones under construction. As well as a lot of conversion experiments. These things need time when huge interests are fighting against it.

[@heronimousbrapson863]

Thank lobbying by the coal and peteoleum industries.

[@Zamolxes77]

Because it will break the monopoly on energy production. Imagine, I can power my laptop with energy produced 2 miles down the way, in my local city nuclear reactor. No more power lines required, strung over the landscape, no way for the world powers to control the lifeblood of civilization. With cheap, limitless energy, skyscraper city farms become a very cheap and desirable alternative, breaking food monopoly. You could buy a variety of foodstuff, grown locally, in the next building over. Now you understand why ?

[@baronvonlimbourgh1716]

@@Zamolxes77 you are basicly describing solar....

[@AccidentalLyrics]

I had heard that there once was a working LFTR decades ago, but no one had specifics, so I was skeptical. Thanks for clearing that up. My guess is that India or China will develop commercial grade LFTRs before we do.

[@roninviking]

Long time Th follower. Brilliant you mentioned Kirk.

[@MehmetlerMehmedi]

Joe, from the bottom of my heart, thank you sir.

[@etmax1]

One thing of great importance with LFTR and could easily be one of its greatest assets in the short term is that you can actually inject a lot of the waste left over from current reactors into the fuel stream and consume/convert it to 300 year life waste from the usual 10,000 year waste

[@thp8485]

That's awesome. Any resources I could learn more about?

[@j.f.fisher5318]

Another reason for resistance to MSRs is that the companies who make the fuel pellets are the same companies that make the reactors. Imagine if the oil companies also made cars and engines. How eager would they be to make cars that were 100x as fuel efficient?

[@linusromey561]

Kodak invented the digital camera, but chose not to develop and market the technology because they thought it would cut in to their lucrative film sales.

[@ArtoPekkanen]

I like your videos :) very inspiring stuff.

[@aplacetorant.810]

Thanks for this. I’ve just used this as physics revision for my GCSE I’ve got tomorrow. Thanks mate

[@JohnSmith-vz8pc]

Now you can tell your Physics teacher that your fridge works by compressing the air inside it, and putting the heat in the coils at the back.... 😄

[@geeksandnerdsrule9199]

I've noticed a LOT of youtubers flashing something on the screen (sentences and so forth). Why?! No one reads that fast. I would greatly appreciate it if you (and all other youtubers who use this practice) would leave the words up long enough to be read. It triggers anxiety in those who need to know what it says.

[@SovietReunionYT]

+1

[@tylerherr4288]

use the frame by frame its for back/forward

[@geeksandnerdsrule9199]

@@tylerherr4288 Thank you.

[@douglasbernal8606]

what time?

[@softb]

Subliminal messages lol

[@JavierCR25]

Joe makes complicated things easy to understand.

[@joescott]

If I can get myself to understand it, that's 90% of the battle. :)

[@ReidPink]

Joe make complicated, easy-to-understand things. haha Just kidding

[@JonathanSchattke]

by introducing many needless errors?

[@JavierCR25]

No, by giving a good basic explanation upon which you can do further research and learn.

[@spuriouseffect]

Solar is on it's way to 4 cents per kwh in the next 5 years. No other form of energy will be able to compete.

[@DjVojto]

shout out for those who worked on those meltdowns and risked their lives no mater the politics, no matter the profit, no matter their families.

[@pinballpsycho]

Kirk's videos are great.

[@Xylos144]

Hey. First off, very well done video. A lot of people have tried talking about thorium and molten salt reactors before... and they tend to do it very poorly. You actually hit all of the major concepts in pretty good detail. I'll be sending people to this video if they have interest in a primer on the technology. With that said, I'd like to make a few corrections/clarifications to what you said. In many cases these things are 'wrongly explained' but still lead the viewer to the same answer, so I don't really care too much. All the same, in the name of accuracy: 5:14 - Moderator. A moderator doesn't cool down a reactor. Actually it empowers it. To understand this, we have to go for a bit of a walk - though if you modify your video at all to elaborate on this, you can certainly cut most of this detail out. Atoms have a property called a 'cross-sectional area' for neutron absorption that basically describes the likelihood of them getting hit by a passing neutron. This cross sectional area changes with the speed of the neutron. Neutrons moving fast have a very low chance of hitting something. But they have a high chance of causing a fission. Likewise, slow neutrons have a significantly higher chance of hitting a given atom, but are more likely to be absorbed than cause a fission. A good example is Plutonium-239. A 'slow' or 'thermal' neutron has about 100x the chance of hitting Pu239 as a 'fast' neutron. But while a fast neutron has basically a 99% chance to cause a fission, a slow neutron has a 1 in 3 chance of being absorbed, turning the atom into Pu240. Chain reactions rely on each fission producing more than one additional fission. So if one fission releases 3 neutrons, you need the conditions in the reactor to be such that each neutron has more than a 1 in 3 chance of hitting another atom and fissioning it. If the neutron escapes the reactor without hitting any atom, or hits other atoms and gets absorbed instead of fissioning, then it's lost. This is why 'Breeder' reactors often are called 'fast' reactors, or have 'fast' in the name. Because a breeder plant in history has always referred to a Plutonium breeder plant. (U238 bred into plutonium by neutrons from fissioning plutonium). Good neutron economy in Plutonium relies on the neutrons being fast. But if they're fast, they're sure to cause a fission if they hit something... but they can't hit anything. You need to increase the 'critical mass' - the amount of radioactive material in the reactor at a given density - so that neutrons are sure to hit something before they escape. But PWRs and BWRs use Uranium-235. And those designs are based on thermal neutrons. Uranium-235 is more unstable than Plutonium, and is much more willing to fission even when hit by a slow neutron. As a result, you can get away with much smaller critical masses. But uranium fissions don't produce thermal neutrons. They produce neutrons of medium and high speeds mostly (it's a statistics thing). To make a Uranium Bomb, you enrich about about 5kg of Uranium to 90% U235. This 5kg is in two pieces - like a small cylinder and a ring. Insert and go boom. By contrast, inside a reactor, the Uranium is only enriched to about 3% U235. it is IMPOSSIBLE for the Uranium fuel rods to fission on their own. There just isn't enough U235 packed together tightly enough in a reactor. However, if you somehow slow down the fast neutrons coming off of Uranium fissions into slow neutrons, then they will be much better at hitting the Uranium and fissioning. How do you slow down a neutron? You use a moderator. A moderator is basically a material that contains hydrogen. Like water, or graphite. Since hydrogen is just 1 proton, it weighs about the same as a neutron. So the transfer of momentum works out really well - like the cue ball hitting a billiard ball. Canada's CANDU reactors use heavy water - which is water with Deuterium instead of Hydrogen, because it's an even better moderator. It's so good they don't even need to enrich their Uranium at all. 0.7% natural uranium is a high enough concentration when using heavy water. So in a PWR or a BWR, the water serves as both coolant AND moderator. If the water leaves the reactor, the chain reaction dies and the fission stops immediately. Actually, this is very important for how nuclear reactors are controlled. How do you perfectly keep a constant rate of 1 fission causing exactly 1 other fission? If it caused any more than that, you would get an exponential growth as 1 becomes 2, 2 becomes 4, and 4 becomes a nuclear bomb after a few more generations. You use negative feedback. If each fission in a reactor starts to cause more than 1 fission, you're going to start producing more power. More power means more heat. Heating up the water causes it to become less dense. Water being less dense means there's less of it in-between the fuel rods, so the fast neutrons are less likely to hit it. Fewer fast neutrons being moderated means fewer slow neutrons, which means fewer collisions with uranium and thus fewer fissions. More fissions causes less dense moderator which causes fewer fissions. Likewise, if you're getting fewer than 1 fission per fission, the water cools down, becomes more dense, moderates more, and the rate of fissioning picks back up. Moderators are what ENABLE the nuclear reactor to react. If you lose the moderator, fissioning stops immediately. 7:39 - The long-term decay products from Thorium consists mostly of things like Strontium and Cesium isotopes. These have half-lives of about 30 years. The '300' year number is not the half-life, but the duration of 10 half-lives. 10 half-lives is the rule of thumb for 'safety'. So basically after 300 years, the fuel would no longer be considered [that] dangerous and you could basically bury it in the environment and not care because it would be indistinguishable from background radiation, or at least well below safe limits for human contact. 9:02 - The lack of pumping is definitely what caused Fukushima. Fukushima, upon detecting the Earthquake, well before the tsunami hit, immediately inserted its control rods and ceased all fission. The radioactive isotopes leftover from the split uranium - the fission products - were what continued to produce heat. The reactor was shut down, but even when shut down cores still produce waste heat which must be removed. If it's not removed, the cladding on the fuel rods can melt, as can the fuel itself, exposing the uranium pellets and the cocktail of radioactive chemicals inside them to the coolant water. Being a BWR was more significant here, because the system allowed for steam to exist inside the main coolant loop. Since steam doesn't cool at all compared with water, the tops of the control rods became uncovered when enough steam was there - leading them to melt from the top very quickly as not even natural convection could help take away the heat. If you need to vent the pressure in the colant loop for any reason, now those radioactive fission products get released outside with the water, spreading out and contaminating the area. This is how nuclear reactors have the potential to be dangerous to the surrounding environment. 9:28 - Thorium Reactors do rely on breeding Thorium in-situ, but it takes about a month for Thorium to go from getting hit with a neutron to becoming U233. Cutting off neutrons from the Thorium is not how a LFTR arrests itself in the case of an accident. In a PWR you have solid fuel generating neutrons, with a liquid moderator. In an MSR, the fuel which is the source of the neutrons, is dissolved in the molten salt. And instead in the reactor are solid Moderators - namely graphite. The source of the neutrons is the fuel itself. Draining them to the fuel tanks does not remove the fuel from the neutrons. it removes the U233 fuel from the moderator, so that its chain reaction dies out and fissioning just stops. There is no source of neutrons left in the reactor. Basically this is identical to a PWR: separate fuel and moderator, and you stop fission. With a PWR, you remove the moderator because it's the liquid of the pair. In an MSR, you remove the fuel because it's the liquid of the pair. The difference with the MSR is that since you're moving the fuel (and the decay products within it that produce that extra heat that destroyed Fukushima) you can move it to stainless steel holding tanks that are designed to be giant heat sinks which can passively remove all the heat without any sort of pumping action. That's what makes the MSRs safe. Before they get hot enough to damage the reactor, the freeze plug will melt, seperating fuel from moderator, stopping all fission, and putting the fuel in a holding tank to passively reject decay heat. It's a safety mechanism that work so long as gravity stays on. And as you correctly stated, this system isn't pressurized because the salt stays liquid up until ~1500C rather than 100C for water. So even though the decay products are in the liquid, you don't have to worry about accidental or deliberate venting. Because the decay products won't fly off into the air and contaminate the area for decades. It'll just sit there like lava.

[@Xylos144]

10:33 - High temperatures don't [necessarily] mean that more water gets boiled off. The temperature of a reactor has to do with thermal efficiency, or Carno efficiency. The compressor on your fridge is something called a heat pump. Basically, rather than using 1KWH of electricity to generate 1KWH of heat, you can use 1KWH of energy to pull MORE than 1KWH of heat from one environment into another environment. The efficiency is Th/(Th-Tc). So for your fridge, inside lets say its 0C, and lets say your house is at 27C. Convert to Kelvin and Th = 300, Tc=273. Efficiency = 300/(300-273) = 300/27 = 11.11 = 1100%+ efficiency. Your fridge spends 1 KWH of electricity to remove 11KWH of energy (as a theoretical maximum - real efficiency will be less than that). But TANSTAAFL. If you can move a lot of heat in exchange for a little work, then the reverse is true. You only can generate a little bit of work from a lot of moving heat. Flip the equation for generation. Efficiency = (Th-Tc)/Th. Lets try running a reactor at regular boiling water temperatures - 100C. And lets say ambient temperature to outside is 27C. Th = 373K, Tc = 300K. Efficiency = (373-300)/373 = 73/300 = 24%. Basically for every 1KWH of electricity we want, we need to produce 4KWH of thermal energy. And that's a theoretical maximum - in practice we'll get much less than that. That's just too inefficient. To get an efficient enough system to be economical, they run nuclear plants at 300C. Th = 573K, Tc = 300K. Efficiency = (573-300)/573 = 47.6%. Still less than 50% efficient, but good enough to work. Although to keep water liquid at 300C, you need to pressurize it to 90 to 150 Atmospheres. A reactor is a giant, 20 foot tall, 9 inch thick nuclear scuba tank. That concrete sarcophagus that surrounds the reactor, which can win in a fight against a Boeing 747, isn't there to contain a nuclear explosion. It's to contain the steam flash if a pipe bursts and all that super-critical water tries to rapidly expand by over 1000x. So a Molten Salt reactor is more efficient because higher temperature means higher thermal efficiency. Just to get the salts liquid, they need to run at 400C. Planned operating temperatures would be more like 700C. Efficiency = (973-300)/973 = 69.2% efficient. Much better. You generate more work for the same input energy when that energy is in the form of a higher temperature medium. 10:53 - While material degradation is a reality of using salts, and these plants wont have the 80-year lifetimes that PWRs do, it's worth pointing out that the plants truly will be small and modular. Think a trash can versus a school bus. Both in material quantity and complexity. In most realistic plans, the modular plants, once done with their lifetimes (which may only be 4 to 12 years) will be taken away to a reprocessing fasscility, with a new canister delivered and dropped into the plant. Projected maintenence on the containment vessel is closed to zero. The graphite moderator inside will likely degrade before the reactor walls. The salt is corrosive, but Hastelloy-N developed during the Oakridge experiment basically proved itself to be sufficiently resistant for long time-spans. Ie, the expectation is little or no maintenance, and just junk (ie recycle) the reactor once a relatively short lifetime has expired. I don't think anything you said was wrong here. Just adding some elaboration. 11:07 - You can definitely make a bomb with the fuel, sort of. It's easier to make a bomb with U233 than with U235. Only 12% vs about 20% enrichment is necessary for a critical mass. During the Manhatten Project, they initially looked at U233 bred from Thorium as a source for the core material. The reason people say you can't make a bomb out of it, is because of that nasty U232 you mentioned a bit later. U232 is a hard-gamma emitter. Which means anyone that tries to steel U233 will kill themselves to death from the radiation. And any boy Scout with a Geiger counter could track down their location. Then physically building the bomb core out of it and assembling the weapon will involve very difficult and expensive remote handling (lest they, once again, kill themselves to death from the radiation). And then the shelf-life of the bomb will be terrible because the U232 radiation will mess with the electronics, and the explosives, leading to the bomb being potentially unreliable and also prone to self-detonation. Separating out the U232 from the U233 would involve Uranium Isotope separation, which is totally a mature technology. But again, the U232 means handling it safely is incredibly difficult. All your centrifuges will become contaminated. And you'll be trying to separate out isotopes of 1 mass unit difference out of 233, rather than 3 mass units different out of 238. Significantly slower, more expensive, more energy intensive. it is not at all impossible to make a nuclear bomb from U233, especially because you don't even necessarily have to enrich it. it's just MORE difficult to deal with the U232 contamination than to mine raw Uranium out of the ground and make a U235 bomb. That's why the manhatten Project abandoned U233 - it wasn't worth the effort. That said, there is suggestion that basically a LFTR would artificially add U238 to the fuel to basically down-blend the U233. Now you HAVE to enrich the uranium, not to get rid of the U232, but the U238 so you can actually get a critical mass. But the U232 is still there wreaking havoc on everything you try to do, so it's Definately more inconvenient than just enriching natural uranium mined out of the ground. incidentally, U232 is why we haven't used Thorium for any nuclear reactors up to this point. Because processing solid Thorium oxide fuel to pull out the Uranium is too expensive and dangerous because of said U232, among other things. India has been trying for decades with little to show for it. Molten-Salt reactors are the real special thing here. You can run MSRs off U233, U235, or Pu239. The reason Thorium is treated as synonymous is because Thorium ONLY makes sense in a MSR, because you can breed the thorium into U233 while its in a liquid state, in-situ, without ever removing it from the reactor. So you don't have to deal with that U232. Any viable Thorium-fueled reactor will be an MSR, though an MSR need not be run off thorium. 12:18 - Fun fact. That reactor at Oakridge holds the record for the highest operating temperture out of any nuclear reactor. Somewhere up in the 900C range. During a test, a control rod kind of got stuck and the reactor started warming up. But because of the same principle as above with negative feedback, it self-arrested. In the case of MSRs, higher temperatures means less dense FUEL rather than Moderator, but the effect is still fewer fissions. Control rods alter the set-point, like the cruise control on your car. The Negative Void Coefficient is what keeps the reactor running right at that set-point. Something also rather unbelievable about the reactor. They'd finish up on friday, shut it down, and start it back up Monday morning. Cylcing a reactor on and off like this is virtually unheard of. It screws with the fuel loading, and a bunch of other things. But in an MSR, the fuel is constantly mixed because it's a liquid. And you don't need to worry about keeping the reactor pumping while not fissioning, because it's in those nice passively cooling storage tanks. 12:30 - You're correct here. The PWR/BWR and the Fast Breeder Reactors were not pursued because the government wanted to get nuclear material out of them. You can't make a bomb out of Plutonium from a nuclear reactor. It cooks for too long and the Pu239 gets hit with neutrons making Pu240 and Pu241, which kill fission reactions. Plutonium isotopic separation is not at all a developed technology. They were pursued for basically two reasons. One is that they already had a lot of know-how with uranium and plutonium, so they liked to stick with what they were comfortable with. As you say, intertia. A second consideration is that those projects were all being done in Southern California, and Kennedy wanted to concentrate all efforts there because it was good for his constituents. So Oakridge's funding got cut for the MSR. Once again, great video.

[@csehszlovakze]

The most comprehensive video on the subject is Gordon McDowell's 6.5 hour video.

[@AvrahamYairStern]

I saw this not long after I saw Sam o'Nella Academy's video on it, must have been a popular subject at this time.

[@ItsMEE-bz9fp]

You're my favorite badass nerd! Always great content, even this episode from 2 years ago that I'm just now watching. You crack me up everytime while informing us on interesting topics ✌️🏻

[@kenulamusic8582]

Yo tks man for dis...

[@davidmckinney5343]

A couple of errors here. The molten salt reactor experiment at Oak Ridge in the 60's did not use thorium. Only U-235. Thorium was the next step, but they never got there because funding was cut. And U-233 only makes crappy atom bombs (for a variety of technical reasons). US built and tested them and said "nah." I very much want to see molten salt reactors that use thorium. This is an idea whose time . . . should have come long ago.

[@hopeless3542]

Joe: you're funny. Thanks for your effort. I appreciate you. blah blah blah. keep up the good work chap, man, creator, guy.

[@myusername111]

Hey man I absolutely love your videos I watch them every night before I go to bed

[@ksb2100]

I hope we can get an update video on this topic.

[@code4chaosmobile]

Have you thought of putting audio only versions on SoundCloud?

[@joescott]

I do that for a podcast, but it’s not on SoundCloud.

[@chriscavanagh1347]

The opening diatribe about Chernobyl had multiple inaccuracies that feed into the fears of nuclear power danger.

[@Grumpollion]

Yup. Notice that these disasters did not occur at Three Mile Island, because of appropriate design.

[@nicktombs1876]

@@Grumpollion only because your government hushed up the amount of radiation leaked at 3 mile island.

[@Grumpollion]

Nick Tombs You’re lying

[@chriscavanagh1347]

@@nicktombs1876 But, Nick, you cannot argue that anybody was harmed by radiation at TMI. Radiation is a very overrated risk. The requirement for radiation dosage for nuclear workers is below the level for airline pilots and how many pilots are dying of radiation effects: no discernible difference from the general population. The hysteria over radiation is one of the primary reasons for nuclear power being relegated to pariah status while we desperately need it to combat fossil fuel-powered global warming.

[@Patchuchan]

@@Grumpollion Three Mile island harmed didn't harm a single person as the containment systems did their job. LFTR would not be able to fail in this manner because the core is already molten and the core material has a negative temperature coefficient.

[@dreamburn1]

Fantastic presentation. You rock like Half Dome.

[@SingleTrackMindState]

Thanks Joe

[@Glurgi]

Good video, I wouldn't mind hearing more about thorium and other large scale energy alternatives :) Kirk Sorenson have pretty good videos about thorium/salt reactors for those interested, pretty sure they will be needed just to handle the nuclear waste problem.

[@jeremyO9F911O2]

Glurgi technically Kirk doesn't make the videos. Gordon McDowell does them, but he's tight with Kirk.

[@Glurgi]

Fair enough, I stand corrected :)

[@chrisgarcia6098]

I can't express how happy I am to have more than one video a week. The quality hasn't dropped at all, but still don't over work yourself !

[@joescott]

This one was a beast.

[@chrisgarcia6098]

Joe Scott it shows ! That was a lot of info, I had to watch twice to soak it all in. And one more time just cause it was good.

[@1964_AMU]

Enrichment of Uranium is putting aside U235 and collecting U238 contained in the first isotope. One ton of U235 contains traces of U238, sometimes from 10 gr to one Kilo, depending from the orignin. A machine turning at high speed is used to extract the U238, it is called a centrifuge.

[@carlchristensen1628]

Thanks for the informative program. In your research, did you come across the Toshiba 4S fast-neutron reactor project? It seems a very viable distributed solution.

[@thomascharlton8545]

Thanks Joe for a well done presentation and spreading the word on thorium power technology. * Sadly, widespread implementation of this concept has been stifled by the trigger word “nuclear” and bureaucratic inertia. * With luck we’ll have fusion tech . . . someday? * We could benefit from thorium now. Regards, Tom Charlton

[@risingpower3658]

Thomas. No fucking leadership. Let's call it what it is.

[@davidelliott5843]

Sadly there are so many rigid opinions Solar = good Nukes = bad. Explain molten salt and thorium to an anti nuke protestor and they wont listen. Explain it to a traditional nuke engine and all they can think is how its not what they are used to. A presenter from Atkins (different vid) said it would be at least 50 years before thorium comes on stream. Why so long?

[@bryanbarnard4094]

Thomas Charlton luckily China and India aren’t concerned with western ignorance based hysteria.

[@bryanbarnard4094]

David Elliott China is planning on a LFTR prototype by 2020

[@RichardKuivila1947]

Don't worry. The Chinese are working full tilt on LFTR's. They have TON's of Thorium pilled up from their Lithium processing efforts. (ps- Nuclear in Chinese translates to "Happy Stuff".)

[@lesliefranklin1870]

I didn't know that "The Oak Ridge Boys" were involved in this stuff, besides music.

[@dougmoreable]

Thank you

[@priyayadav9012]

Amazing bro I love how you say Thorium!😎

[@gonzalogonzalez4681]

Joe, love your content. The safety advantages of molten salt reactors cannot be overemphasized. Someday people will wonder why we ever even considered building any reactors in the fukushima style, that could blow up from a bleeding plumbing failure. The first "walk away safe" reactor, no matter what it burns, will cause a revolution in peoples thinking. I do have an issue with your video. The watcher comes off with the impression that molten salt reactors and thorium are connected. I would hate for people to lose enthusiasm for molten salt reactors because of some mistaken notion that they need a thorium fuel cycle to work. All actual molten salt reactors, including the Oak ridge reactor, used uranium, which is just as well suited as thorium to all salt designs, including liquid fuel. Yes, the Indians go on and on about the "phase 3" future, but their MSRs use uranium. It is hard to justify development of a new nuclear fuel when uranium fuel at

[@wilsonriley1856]

One of the goals behind making thorium reactors is that it would be able to be acquired cheaply from rare earth element mines in the US, as you tend to get a lot of thorium as a waste product. If a thorium reactor actually gets going, I would expect the price of thorium to become appx. 1/4-1/5th that of Uranium due to the ability of rare earth element/heavy mineral sand mines to increase production and dispose of waste.

[@stephenh5944]

Gonzalo Gonzalez - the PWR was designed to meet the needs of the US Navy. After they did the research and started using them, everyone else just jumped on the bandwagon, without really considering if this was the best design for power generation.

[@sergiokorochinsky49]

nuscale is NOT a Molten Salt Reactor.

[@paulbedichek2679]

Gonzalez,I keep trying to make this point, but you worded it so much better, really interesting how intelligent, well meaning ,pro nuclear people can get such simple ideas wrong. No need for Th in NuScale or any Triso design,coold by molten salt like Kairos Power or Helium like X Energy,th closest thing w have in the West is th ThorCon,which will be built in Indonesia using HALEU and Th in molten state,Trrestrial Energy uses an IMSR U and Th. Th is a proliferation risk as for a LFTR you need enriched Li one of the main ingredients of a thermonuclear device. Fast reactors such as Natrium system are better at removing proliferation risks..

[@unsettledroell]

In my opinion, the worst dowside to LFTR is the huge amount of graphite in the core. Graphite degrades and has to be treated as waste since is will become highly radioactive. The best way to do thorium is doing it in the fast spectrum; so no moderator like graphite or water. The MSFR (molten salt fast reactor) will be doing this. MSFR also has much less chemical processing requirements than LFTR, and deliveres much more power per core (3000MWth) Definately worth looking into

[@brian2440]

If youre developing a fast reactor, why would you chose U-233 fuel over Pu-239 or high energy Uranium 235?

[@JonathanSchattke]

Brian undeniably better breeding in thorium/u233 cycle. The rub is getting transitioned.

[@brian2440]

Why does thorium 232 have better breeding? Additionally my challenge was not based on breeding, but rather that Plutonium 239 is a better choice for a fast breeder reactor. Pu-239 has a higher probability of fission under high energy or fast spectrum, due to a larger cross section. Uranium 233 is better for thermal spectrum, because it has a lower probability of neutron absorption at the thermal spectrum.

[@JonathanSchattke]

Brian the fuel utilization (fraction of neutrons hitting a fissile atom which cause fission) is better. Plutonium you end up spending 30% of your neutrons on making transuranics instead of energy. U233 its only 10%. And that means you need to breed 1.5 times as much in a U/Pu breeder.

[@brian2440]

Jonathan Schattke Ok, but does this benefit make up for the loss of fission production in fast spectrum compared to that of plutonium?

[@johnbyrne4438]

Great video! Sometimes one just has to hear it from the right person. Now I get it. What about Taylor Wilson and his idea?

[@flirtwithdanger_les]

About the only vid I've found which gives an easy-to-understand pros-and-cons of LFTR

[@schmetterling4477]

The pro is that it makes expensive energy. The con is that it makes expensive energy. What was the question, again?

[@georgeshevchuk6770]

If you want to know about Thorium Molten Salt Reactors, the guy to listen to is Kirk Sorensen.

[@JonathanSchattke]

6:13 The only Transuranic used to "melt cities" is plutonium, bred special for the purpose. No one has ever used a commercial power plant to make bomb material.

[@johnmasursky7717]

where do you think the US got the Pu238 to make over 60,000 nuclear weapons? In fact, that was the primary reason that after WW2 U235 was chosen for the first power reactors: it has PU238 has a waste product. And this is why the US gov't has been taking all that waste (after a few years of cool down) from commercial plants. They wanted the Pu238 in it to make bombs; it was easier than producing U235 for bombs.

[@M0rmagil]

Uh, U238 makes up 99% of the Uranium we dug up out of the ground. It’s not hard to acquire. We don’t use enriched uranium to make bombs. We don’t even use the waste to make bombs. In fact, we don’t do anything with it because we haven’t even built a reprocessing plant.

[@yeomantrader9505]

You were absolutely right.... I didn't' think you were going to get there...but you did. And all at one atmosphere. :)

[@gregspencer793]

@Joe Scott you should do a video discussing the CANDU reactors which use U238 and as well as a variety of other materials other than U235

[@marioromero5068]

I hope we pick the MSR technology again before its to late.🥇🌎

[@Etheoma]

A Thermal spectrum reactor literally would not work without a moderator as the consternation of fissile materiel would be much to low to sustain fission So no the moderator is not there to "stop it from going out of control" the neutrons need to be slowed down so they can be captured U235 in low enriched uranium, otherwise you would need much higher enrichment to go critical -going critical means that you are generating as many neutrons as you are consuming so you can sustain fission- this is why proposed fast reactors (fast= fast spectrum neutron reactors where there is no moderator to slow down the neutrons) need much higher enrichment of uranium or the actual realistic way you would do it is it would be plutonium breeder reactor, so while the cost of the fuel to start up the reactor would be high your feed would be natural uranium which would be transmuted into plutonium through the normal operation of the reactor, so you would more than re-coop that cost over the lifetime of the reactor. Also Thorium isn't really the magic behind 95% the benefits of a molten salt reactor, it's the molten salt reactor that delivers those benefits. Yes Thorium is much more common so fuel costs would be lower, but even in current reactors fuel costs a negligible and that is when we only burn about 5% of the fuel, where as a breeder reactor can use 90% to almost 100% of the fuel, so just there your fuel costs are cut by 20x, also due to the higher temperature operation of molten salt reactors they are naturally more efficient and can be used with closed cycle super critical CO2 gas turbines, which raise the efficiency of turning the thermal energy into electricity from 10% - 20% to 45% so that also halves the fuel consumption. The only real reason for going with a breeder reactor and using more efficient methods of energy generation is to reduce the waste stream, you can do a fast plutonium molten salt breeder reactor also, so even though the fuel will be more expensive and you need higher concentrations of fuel and higher enrichment to start up the reactor. It's really not a big deal as the fuel costs will be truly negligible even when you consider that the build cost of such a reactor should be significantly lower due to not needing to have the reactor under at least 70 atmospheres of pressure which necessitates ~20 inch think reactor walls which also have to be prefect means that the reactor cost is higher and the number of places that can do it are limited. Where as a molten salt reactor would be under something like 5 atmospheres of pressure simply to pump the fuel around the reactor, so you can go with 2 - 4 inch thick steel which can be done pretty much in any factory, although the standards would be to those of building an air craft so it would still be expensive because of all the validation you would need to do, but the actual reactor vessel and guts should only cost couple 100 million after the economics of scale kick in, you would likely however at first probably be looking at more like ~1 billion to start off with, but that is still cheaper than conventional reactors. Oh btw fast reactors do have there benefits of a much better neutron economy due to the fast neutrons which have a much better likely-hood of causing fission if they hit, but have a lower chance of hitting in the first place, so you have more neutrons than you need which makes it easier to break down actinides which is your main problem in nuclear waste which brings down the time until the waste is safe to 300 years apposed to 10k years. It also means you don't need to condition the fuel nearly as much and can just pull out fission products, where as you need to constantly process the fuel in a thermal spectrum reactor, so running costs and build costs would be higher and would outweigh the benefits of a cheaper more abundant fuel. Also you can start off with fast uranium molten salt burner reactors sooner which can consume nuclear waste from conventional reactors and you can keep the spent fuel around for 30 years then when fast plutonium molten salt breeder reactors come around. Although honestly I would like to start off with breeder reactors as there will be little impetus to move to breeder reactors until we run out of fuel.

[@domingo2977]

Thank you so much for telling me the downsides.

[@johanneswestman9315]

Slight correction(but with a huge impact). Graphite moderators doesn't absorb neutrons. It slows them down increasing the odds of a fission reaction when the neutron hit another uranium atom. In other word - the graphite moderators actually increase the rate of fission rather than decrease it.