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The intuition of 'fast neutron hits nucleus and smashes it to bits' is not wrong; fast neutrons can split U-238 for that very reason. But cross-sections in general decrease with neutron energy (for subtle physics reasons) and since a neutron 'falling' into a U-235 nucleus reaches it going fast enough to split it apart anyway, you're better off using slow neutrons for that.
You mention that natural uranium can support a chain reaction, if it's moderated. The amazing thing is that this has happened! While processing ore from the Oklo mine in Gabon, they found that there was about 20% less U235 than there should have been, and the ore also contained fission products. The conclusion was that the ore itself had been operating as a water-moderated nuclear reactor, about 1.7 billion years ago. However, this is cheating a bit, as natural uranium was about 3% U235 at that time.
yes, the Oklo reactor is a marvelous example of "Nature did it first." This is precisely why I say "first artificial self-sustained nuclear chain reaction" when talking about Fermi's Chicago Pile I, because Nature already did that at Oklo.
@@jkzero didnt groundwater/floodwater act as a neutron moderator and start the critical reaction until the water boiled off? Only to sit dormant until the water filled the void again?
@@SubvertTheState yes, that is exactly what it is suspected to happen. Oklo was a naturally periodic on-off nuclear reactor. Sorry Fermi, you came second.
From what I've learned, there's some dispute over whether a small portion of the Chernobyl reactor may have had a prompt critical excursion (which is still not the same as a bomb but would be similar to a fizzle, and would mean that some portion of the energy in the explosion came from the nuclear reaction itself not just from the steam and heat).
Came here to say this. But even if that is not the case, a non-nuclear explosion can still be a very, very bad thing. And even in the case of Fukushima where radioactive release was much less than Chernobyl, cleanup costs are expected to top the equivalent of several hundred billion US dollars. Some people are estimating the figure will top one trillion US dollars by the time it is completed.
Great video as usual, the math and technical details are very well explained and it also helps spread awareness on the reality of nuclear power as its very misunderstood with the general public
I am glad that the math is clear, I have done my best to avoid using calculus for the explanations because I want to reach a wider audience. Also, the topic of this video is something I have intended to create for years because I get this comment from anti-nuclear pseudo-environmentalists. Nuclear reactors are safer, more reliable, and cleaner than any other source of power.
@@jkzero absolutely, its like the discussing if planes are safe, nuclear energy could help a lot with climate change but its definitely under utilized especially at the moment with the trend of shutting down reactors, lets hope things change in the future. You are truly doing a great job with this channel, keep going forward you have our full support!
@@cewkins721 tell me about it; I live in Germany, the land praised for their "Energiewende" that shuts down perfectly running power plants to replace them by their dirties coal plants. It is just terrible.
@@jkzero yeah i am aware, big mistake from the Germans, though it was all really Driven by fear and drama with the impulsive action to stay safe after Chernobyl and the incident in japan than to understand why it happened
Glad you enjoyed it! I just ask to support the channel by liking and sharing so the mighty algorithm can find more people interested in these fascinating topics.
Glad you enjoyed it. I just ask to support the channel by liking and sharing so the "mighty algorithm" can find more people interested in these fascinating topics.
I was recently discussing this topic with some friends. Understanding that a reactor cannot explode exactly like a nuclear bomb, a question was raised about a possible steam explosion. Chernobyl as an example: can a steam explosion, generated by nuclear heat, be considered a "nuclear" explosion? We tentatively concluded that it was subjective, since the root cause is usually due to uncontrolled nuclear reaction of whatever cause. Using a nuclear warhead as an example... The explosion is actually a result of a sudden release of energy "generated" by nuclear fission. The sudden release is made possible by the bomb casing, containing the reaction for as long as possible until it is finally overcome. In the case of a reactor explosion, the energy is transduced to steam pressure; howbeit, a few extra layers of procession.
Just got done binging Chernobyl. Always great to come back to your science, Jorge. One thing that really showed up a lot in that show was the term “void coefficient” - would you care to one day explain the science and math behind that, and perhaps elaborate on common reactor designs?
a few years ago I wrote an article about my thoughts after watching HBO's Chernobyl (I used to write on a blog, in Spanish but Google Translator works quite well). Check it out here conexioncausal-wordpress-com.translate.goog/2019/06/23/chernobyl-reactores-vs-bombas-nucleares/?_x_tr_sl=es&_x_tr_tl=en&_x_tr_hl=en&_x_tr_pto=wapp
Great vid as always! but I have two questions to ask? The first one is in a nuclear device's initiator what type of neutrons is being produced slow or fast ones? The second one is when a atom got split what type of neutrons is produced slow or fast ones?
thanks for the comment and the questions, I love triggering more questions than providing answers. In this I can provide the answer to your questions: in both cases the neutrons are fast; which is no surprise; otherwise, they would not had been used. A bomb requires fast neutrons because the chain reaction is very fast, of the order of a micro-second, as calculated in the video "The Physics of a Nuclear Explosion." Slow neutrons are useless for a bomb because they are... well.. slow. Also, the secondary neutrons produces by fission are always fast, this is why a reactor needs a moderator as mentioned at the 08:13 mark.
@@jkzero thank you!, so in a nuclear device, the goal is to split the nuclei by not moderating the fast neutrons by using a moderator like graphite or water but by adding enough fissionable mass so at some distance after many cloisions the fast neutrons will be slowed and then it will be able to split the nuclei., if the density is increased too much k is more than one then the fission reaction is going to be exponential "explosive", is that right?
@@moodi6780 you got it, that is exactly right: in a bomb you want the chain reaction to go wild, a runaway reaction as fast as possible (this is why fast neutrons are needed) so the nuclear core is fissioned multiple times before it blows itself apart. Otherwise, you get a fizzle like the shot shown at the end of the video. In a reactor, on the other hand, the reaction is controlled by neutron absorbing materials but also the neutrons are slow so there. Important is that a reactor is NOT a controlled nuclear explosion, this is a classic misinterpretation. In a reactor there is no nuclear explosion because neutrons are slow and the uranium is not enriched.
Did you miss speak around 12:25, “fast neutron simply cannot produces a chain dreaction”? Your fizzle explanation is correct. However a bomb requires fast neutrons. This is all enrichment dependent for slow neutron.moderated power reactors. What about HEU reactors? What am I misunderstanding?
Thank you for the informative video. I have 2 questions that I hope you could answer. First is, which library did you use to obtain the values for the various cross sections? Second, at 11:26, you wrote that lambda_f is the same for both fast and slow neutrons. Why is the fission mean free path the same for fast and slow neutrons? Thank you.
I’d be very interested in a comparison between U and Th cycle for civilian usage. There’re a lot of hype outside, that would be great to present the reality of each. And someday fast neutron reactors.
Thanks for bringing this up, I am aware of the hype around Thorium reactors and I have not been able to make up my mind on this but I could reach to some expert in the field. A few years back I was invited to a special meeting of nuclear scientists in Sicily. In the bus from the airport I met a guy and we began talking about nuclear reactors, he turned out to be Kirk Sorensen, one of the most vocal advocates for Thorium reactors. We spent a week in the island with other nuclear physicists, great guy. But after he convinced me that Thorium was the solution, he even gave me a copy of his PhD thesis, which I read completely; I am still not sure that Thorium solves all problems or if it solves problems that are not there. I will ask around for an update, I think this is a fascinating topic, I should probably read his thesis again.
Thorium fuel cycle is a pipe dream IMO: 1. Different chemical process for fuel production, so building completely new production chains is required. 2. Pa-233 has a huge half life - 27 days, which slows down refueling process and requires more safety control. 3. U-232. Makes operations with spent fuel almost impossible due to high-energy gamma-quants. Tldr: MOX fuel for the win!
Yes. But isn't there a scale factor that needs to be taken into account? The bigger the bomb, and the lower its "density" the bigger the fast/slow neutron ratio effect on yield would be? So is there a lower size limit below which you would actually want to use slow neutrons for a bomb? Or is this size threshold just so far outside of buildable object sizes that it's not relevant?
Does this apply to the scenario in the sci-fi/horror film ALIENS, where the nuclear reactor of the colony on LV-126 was on a countdown to explosion? I can't remember if that was a fission or a fusion reactor . . .
Ah, now I see the side by side comparison of the fast and slow charts have different enrichment fraction scales. Would it be correct to say that commercial power reactors can not get into a high order nuclear explosion because, (1) they do not have high enough enriched fuel, and (2) the reactor is so over moderated that a run away chain reaction (k >> 1) is not possible?
@@jkzero. THANK YOU. With regard to next generation, small modular reactors (SMR), core designers want to used higher enriched fuel, even HEU. So this can remove one safety constraint. But the fast neutrons may not be adequately moderated either. I am not clear the reactors are feasible for private commercial applications. I believe some military reactors operate on HEU. Perhaps you could do and introductory video on SMR core dynamics sometime. I would like to know how the fast neutrons know how to behave themselves. I know my question is not clear. I guess I’m asking how the HEU core can burn for a long time without refueling.
I am glad that you found the video of interest. I am not very knowledgeable in reactor physics but in case you like to follow well-paced lectures I would recommend the MIT course Introduction to Nuclear Engineering and Ionizing Radiation, all the materials are available online. The lectures are on RUclips and the instructor is excellent.
The Upshot-Knothole series of tests was notorious for its generation of fallout. The above-ground fizzle of Ruth surely generated considerable fallout.
The idea of a nuclear detonation fizzle makes me cringe with nervousness. I couldnt imagine the clean up or lasting actinides being spread all over the place.
as explained at 8:28, a moderator is a material that, when neutrons collide with it, neutrons slow down. Neutrons released by fission move very fast, then they collide with the material (moderator), and after the collision move slower.
A few years back I was invited to give a seminar at the University of Mainz, where they let me poke around their TRIGA reactor. I do not know much about TRIGA reactors other than, being research reactors, they allow you to see the most magnificent blue light that I have ever experienced: Cherenkov. I have a video on Cherenkov radiation in the to-do list.
Dr. Diaz I freely admit I am deficient in advanced mathematics, algebra just goes right by me. However once I discovered that I was born on the anniversary of the bombing of Nagasaki I have taken an interest in nuclear weapons and, as a side effect of that, nuclear reactors. I am finding your series fascinating even though I can't follow the theory completely. The one factor I do not recall you mentioning in this video is Plutonium production in reactors. To my mind it is theoretically possible to create enough Pu in a reactor to make a nuclear detonation but I also know that the geometry of the reactor, combined with the randomness of the distribution of the Pu would make this happening accidentally a practical impossibility. Also the Pu-240 content would make it an even less probable event.
You right about the possibility of plutonium production in nuclear reactors; however, plutonium requires very large amounts to be used for a bomb, in fact plutonium bombs are very complicated because they require a very fast compression of plutonium core and plutonium but be cleaned from other isotopes that ruin the explosive properties of Pu-239. This is not possible in a nuclear reactor.
Thanks, glad you liked it. My problem when I attempt to address this important question is the fact that I can answer it with physics, but in the words of Leslie Knope: 'all I have on my side is facts and science... and people hate facts and science"
I’ve been teaching this premise for years. A nuclear power plant cannot end in a nuclear bomb explosion. The physics just doesn’t allow it to happen. The method used to fission atoms is completely different. Still, I’ve had people tell me I’m a complete nut, and I am 100% wrong. What is that old saying….”it’s hard to win an argument with a smart person. But it is damn near impossible to win an argument with an idiot.”
I get your point. For a long time I wanted to make this video. When someone says "a reactor is just a bomb under control" I say "show me the math, at least I can show you the math of the contrary"
I enjoy a lot your excellent channel, well done! Speaking of the yield, you have to take into account the total mass of the nuclear material also, don't you? Since the uranium content in a nuclear reactor is around 3 orders of magnitudes larger than in a nuclear weapon, this compensates the inverse squared effect of the characteristic time between neutron collisions. This way you end with a yield ratio between a small weapon (utilizing fast neutrons) and a large reactor (utilizing slow neutrons) around 10^4-10^5, resulting in explosion energy in 100-1000 kgs in terms of high explosive equivalent instead of 0,1-1 kgs. Sure, this is nowhere compared to nuclear weapons yield and can be produced with conventional explosives much easier. Some say that the initial explosion at the infamous Chernobyl accident was a low-efficiency nuclear detonation, or rather, "fizzle". The claim is based on evidence examining the ruins of the reactor hall, position of the biological shields etc. Check out That Chernobyl Guy's video on this topic: ruclips.net/video/kuptYyKoDM4/видео.html
To boil water... yes a part of the problem. LWR (reactors used today) use water in a pressure tank. Dangerous and expensive. like an old steam machine. Reactors can howevever be built safe and a lot cheaper , not to mention at least 100 times more efficient, and with only 1/10 initial load. Waste without plutonium. When the research was going well in the 1960s the project was cancelled . Nixon in 1970. An intence propaganda against nuclear energy began, telling a LWR could explode lika a bomb. The most dangerous was the russian RBMK. They were lost in the nazi thinking making bombs and electricity at the same time. Best reactors are MSR , totally safe with no reactor pressure vessel. However ONLY Thorium can come in question as it can run in thermic neutron spectrum, while uranium 235/238 can not. Thanks for a god presentation on the physics of U238/U235/Pu239.
Not sure what difference it makes, whether the explosion is "just" a steam explosion that blows the reactor apart, or a nuclear explosion that ... well, blows the reactor apart. What happened at Chernobyl was sufficiently bad, even if it was "only" a steam explosion.
I think there is a big difference because modern reactors have a massive containment building around them; therefore, a steam explosion will likely not damage the reactor components, and more importantly, to the surrounding area, making nuclear reactor extremely safe to live around. A full-scale nuclear explosion (which is not possible) would completely vaporize any containment around and produce catastrophic damage several kilometers around. Chernobyl was a steam explosion, you are right, and it was terrible; however, the reactors there were designed to fail and didn't have containment buildings. No other nation in the world would have built such time bombs.
Your definition is incorrect. A “fizzle” is a nuclear explosion that exploded below its design yield. However, *it is still a nuclear explosion* The k value is still greater than 1 at the time of detonation but is unable to sustain for long enough to achieved its design yield before it blew itself apart and reduce k value to less than 1. (If only the convention explosive detonate then they would described it exactly that… conventional explosive inside the bomb went but not a nuclear explosion) So, yes a nuclear reactor like Chernobyl could definitely become a “fizzled” nuclear bomb accidentally as the design flaw which allows for positive void coefficient means that there is a possibility of a reactor runaway where power would continue to increase until it basically blew itself apart. Hydrogen/steam explosion doesn’t vaporised 190 tonnes of uranium in a blink of an eye like magic… Chernobyl reactor 4 core was pretty much left emptied after the explosion. The famous “elephant foot” is actually over 90% melted sand with only traces of fission products in it) and all evidences points towards very little of the reactor core are left onsite. (Note Chernobyl reactor cores are gigantic) They were able to sent people right inside the Chernobyl reactor just several months after the explosion… compare to Fukushima which they still can’t get anybody near the reactor after 12 years.
In answer to the clickbait, yes. Several have, deliberately or unintentionally. SL/1, SPERT, BORAX and Chernobyl no. 4 all suffered steam explosions. At Fukushima, hydrogen was generated by the hydrolysis of the zirconium cladding, and that exploded. None of these were nuclear explosions, but they were nevertheless explosions.
Under dramatic conditions, nuclear reactor can be taken to critical scenarios. In Chernobyl the most important factors were the terrible design, bad operation, and lack of containment that led to a a run-away reaction and the subsequent stem explosion. Not a nuclear explosion. Fukushima was different, reactors cores melted down but the explosions were just hydrogen explosions, nothing nuclear either.
I am not aware of this, if there is anything to be corrected on the video I would include an errata, could you share any reference about this explosion from low-enriched uranium? Thanks
@@jkzero Figure 3.1 from this ORNL technical report shows finite critical masses for a bare sphere when the concentration of U-235 is above 5.4%. web.archive.org/web/20131102011417/web.ornl.gov/info/reports/1998/3445606060721.pdf
Can it explode like a nuclear bomb, with a classic mushroom cloud .... No. But that is a false question, and a misdirection. Can a nuclear reactor suffer an in-core nuclear detonation leading to rapid catastrophic disassembly and release. Yes, in some circumstances. It has already happened at least three times, and arguably several or many more. SL-1, KIWI-TNT, and Chernobyl all suffered in-core nuclear detonations and disassemblies. The assemblies could not release more than tens to a hundred tons of TNT equivalent release from prompt fission yield. But tens of tons is certainly enough to utterly destroy the reactor and any containment. Many of the tiny SNAP and SPERT reactors may have crossed that threshold as well. Is this a serious concern for nuclear reactors? Yes. The reactors must be designed and operated in such ways that it is not possible to achieve prompt criticality leading to disassembly (or even serious damage) under any conceivable incident scenario - including especially hostile action by any adversary - internal or external, and from any conceivable accident scenario. It is not enough that the probabilities be low. The consequences are far too severe to allow any such scenarios. This also extends to spent fuel pools and other fissile material storage.
The topic of the video is the fact that a nuclear reactor cannot explode like a nuclear bomb (which stated within the first 20 seconds of the video to avoid misleading viewers), and the title of the video makes clear that this is a comparison of the nuclear reactions taking place in a reactor and how they differ from those in a bomb. Other types of explosions are mentioned at 6:24.
@@jkzero Ah - but that is precisely the misdirection that will mislead viewers, as the viewers are mostly not well versed in nuclear physics or even the consequences of catastrophic malfunctions in such facilities. In many ways the consequences of a lower yield nuclear detonation in-core that destroys the reactor and facility and spreads enormous quantities of radioactive material across the landscape and into the atmosphere is worse. These are potentially nation killing events. Arguably, Chernobyl ended the USSR. Fukushima nearly did the same to Japan, though no in-core detonation occurred there. If such an event occurred in a US reactor in the midwest, it would wipe out much of the US heartlands ability to produce food (both as crops and animals). Farther east and the population impacts are massively larger, but with lower food production impacts. Many of the reactors are embrittled or have extremely questionable primary vessels already, making them more vulnerable to catastrophic failure. Nearly all of them are extremely old making them more vulnerable yet, with embrittlement of all of the nozzles and connections. Some like CGS in Washington State have other serious issues. NRC has allowed CGS to run with a broken bracket on a primary ejector pump in the primary vessel by running with a richly hydrogen environment to reduce oxidative damage to the remaining bracket, and greatly increasing the risk of a catastrophic failure. The nuclear ago of fission is over. It is highly non-economical, and hugely risky, with no path to deal with the long lived radioactive wastes or fissile materials or other actinides. It's time is done. But the industry refuses to go quietly into history.
Also, the comment of other explosions at 6:24 is inadequate. We HAVE observed in-core detonations. In all three that I cited, the reactors were driven deep into prompt criticality. SL-1 was a far over powered reactor. When it was designed the 1 stuck cold rod criteria did not yet exist. SL-1 led to that criteria. When an operator overcoming the jamming of a control against poison cladding, added to reduce the reactors power level, jerked the central control blade nearly two feet upward, he inadvertently set the stage for a prompt critical rise through 25 generations of power rise reaching enormous power levels before the flash vaporization of the coolant, and fuel led to reactor disassembly ending the excursion. But the rectors destruction was already guaranteed by that time. KIWI-TNT was intentionally destroyed by overriding safety criteria, and snap moving the control element far beyond design. That resulted in a similar catastrophic prompt nuclear rise and detonation destroying the reactor. Chernobyl similarly was destroyed by horrifically bad design and horrifically bad operation. The control rods were tipped with graphite that increased reactivity before the nuclear poisons could enter the core. The reactor was then run in a highly unstable regime at low power with xenon build up being overcome by withdrawing all of the control rods. When power rise then began the chief operator order activation of AZ-5 - a full scram - which then enormously added to the reactivity of the reactor and causing a prompt nuclear power rise to levels vastly greater than the reactor could ever handle. In all three cases the result was precisely what the video argues cannot happen - a prompt critical nuclear chain reaction far above unity, resulting in a catastrophic sub millisecond period and a power rise that screamed through the power range and beyond, generating ton to 30 ton TNT equivalent energy yields that vaporized the central core and splattered the rest outward before the negative reactivity insertion was great enough to shutdown the reaction. Even then, delayed neutron generation drove things even higher yet. This is precisely what the vide argues cannot happen. But it did. It did precisely that. By definition these were nuclear detonations, albeit very low yield in bomb terms. But the yield doesn't need to be in the kiloton range to utterly destroy a reactor. And As I noted before, the consequences of destroying the reactor facility are in many ways worse that a full bomb yield detonation. Also, the fizzles mentioned have to be remembered are typically 500 ton yield detonations. Those are enormous detonations even as failures as nuclear bombs or devices. Add to these the many SNAP and SPERT reactors tested to failure by ejecting control elements. Many of these disassembled as a consequence. These were even lower yield nuclear detonations, with low consequence other than to the tiny reactors themselves. The Godiva criticality accident took that a step lower yet, achieving a prompt criticality but not destroying the assembly. The various TRIGA reactors operate in that regime - triggering short lived low Keff prompt criticalities of insufficient power to damage the reactors.
@@tunneloflight I understand you point now, I think you are right. However, using your comment " the viewers are mostly not well versed in nuclear physics," when they hear "nuclear explosion" they all think on a full-scale at-least Hiroshima-like devastation and not the in-core detonation that you describe. But I get your point, thanks for sharing that.
Chernoble and fukushima were nuclear explosions looking inside the fukushima reactor core. Nothing was left of the fuel rods as was the same at Chernoble, in a 1950,s book i read that a nuclear pile will explode with the force of tnt if left to run away.
That's factually wrong. Both were hydrogen explosions. The fuel reached such temperatures that the water in the core turned into hydrogen gas, which ignited. In the case of chernobyl, the entire plant blew up, including SOME of the fuel. The rest continued to react and melt through the bottom of the reaction chamber, forming the famous elephants foot. The same happened in fukushima to a much lesser degree, because the plants were built to withstand such a blast.
Claiming a reactor cannot create an atomic explosions is questionable, especially if we include the waste in the pool (which all reactors should have) . If that pool looses it's water, we can get a critical mass and kaboom.
in the video I show all the calculations that show that a nuclear explosion is not possible, if you could share the equivalent calculation describing how a nuclear explosion can occur with reactor waste I would love to learn.
@@jkzero look like I am not allowed to paste links, The subject of criticality is well understood, Plenty of videos explain it good. Not here to pick a fight but if someone throw maths claiming criticality cannot occurs in or around a nuclear reactor, especially when most authorities on the subject say otherwise, it is hard not to feel an attempt to be misled. As always I also embrace the possibility of being completely wrong. Friendly yours...
Criticality leads to heat and the amount of heat down to the concentration of fiscal material. In a bomb that a concentration is high enough to result in an explosion, in waste it just melts. Two completely different things.
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The intuition of 'fast neutron hits nucleus and smashes it to bits' is not wrong; fast neutrons can split U-238 for that very reason. But cross-sections in general decrease with neutron energy (for subtle physics reasons) and since a neutron 'falling' into a U-235 nucleus reaches it going fast enough to split it apart anyway, you're better off using slow neutrons for that.
You mention that natural uranium can support a chain reaction, if it's moderated. The amazing thing is that this has happened! While processing ore from the Oklo mine in Gabon, they found that there was about 20% less U235 than there should have been, and the ore also contained fission products. The conclusion was that the ore itself had been operating as a water-moderated nuclear reactor, about 1.7 billion years ago. However, this is cheating a bit, as natural uranium was about 3% U235 at that time.
yes, the Oklo reactor is a marvelous example of "Nature did it first." This is precisely why I say "first artificial self-sustained nuclear chain reaction" when talking about Fermi's Chicago Pile I, because Nature already did that at Oklo.
@@jkzero didnt groundwater/floodwater act as a neutron moderator and start the critical reaction until the water boiled off? Only to sit dormant until the water filled the void again?
@@SubvertTheState yes, that is exactly what it is suspected to happen. Oklo was a naturally periodic on-off nuclear reactor. Sorry Fermi, you came second.
😅@@jkzero
Candu reactors use natural uranium and heavy water.
From what I've learned, there's some dispute over whether a small portion of the Chernobyl reactor may have had a prompt critical excursion (which is still not the same as a bomb but would be similar to a fizzle, and would mean that some portion of the energy in the explosion came from the nuclear reaction itself not just from the steam and heat).
Came here to say this. But even if that is not the case, a non-nuclear explosion can still be a very, very bad thing. And even in the case of Fukushima where radioactive release was much less than Chernobyl, cleanup costs are expected to top the equivalent of several hundred billion US dollars. Some people are estimating the figure will top one trillion US dollars by the time it is completed.
The Chernobyl guy got a notable theory about it. ruclips.net/video/kuptYyKoDM4/видео.htmlsi=-4G_ivPkDE2D02EE
More awesome content! Absolutely loving your videos, Dr J, keep them coming 🤘
Bravo. Just one of the best channels on RUclips
Very informative
Great video as usual, the math and technical details are very well explained and it also helps spread awareness on the reality of nuclear power as its very misunderstood with the general public
I am glad that the math is clear, I have done my best to avoid using calculus for the explanations because I want to reach a wider audience. Also, the topic of this video is something I have intended to create for years because I get this comment from anti-nuclear pseudo-environmentalists. Nuclear reactors are safer, more reliable, and cleaner than any other source of power.
@@jkzero absolutely, its like the discussing if planes are safe, nuclear energy could help a lot with climate change but its definitely under utilized especially at the moment with the trend of shutting down reactors, lets hope things change in the future.
You are truly doing a great job with this channel, keep going forward you have our full support!
@@cewkins721 tell me about it; I live in Germany, the land praised for their "Energiewende" that shuts down perfectly running power plants to replace them by their dirties coal plants. It is just terrible.
@@jkzero yeah i am aware, big mistake from the Germans, though it was all really Driven by fear and drama with the impulsive action to stay safe after Chernobyl and the incident in japan than to understand why it happened
Fascinating. Thank you!
Glad you enjoyed it! I just ask to support the channel by liking and sharing so the mighty algorithm can find more people interested in these fascinating topics.
Great video as usual. Would be nice to have a video about how they measure the cross section and neutron numbers in practice.
I am considering a video of the sort "Nuclear Q&A" where I can go through many short questions like this. Noted.
Fascinating. Thankyou.
Glad you enjoyed it. I just ask to support the channel by liking and sharing so the "mighty algorithm" can find more people interested in these fascinating topics.
I was recently discussing this topic with some friends. Understanding that a reactor cannot explode exactly like a nuclear bomb, a question was raised about a possible steam explosion. Chernobyl as an example: can a steam explosion, generated by nuclear heat, be considered a "nuclear" explosion?
We tentatively concluded that it was subjective, since the root cause is usually due to uncontrolled nuclear reaction of whatever cause. Using a nuclear warhead as an example... The explosion is actually a result of a sudden release of energy "generated" by nuclear fission. The sudden release is made possible by the bomb casing, containing the reaction for as long as possible until it is finally overcome. In the case of a reactor explosion, the energy is transduced to steam pressure; howbeit, a few extra layers of procession.
Thanks Jorge for another Master Class!!!!
Just got done binging Chernobyl. Always great to come back to your science, Jorge. One thing that really showed up a lot in that show was the term “void coefficient” - would you care to one day explain the science and math behind that, and perhaps elaborate on common reactor designs?
a few years ago I wrote an article about my thoughts after watching HBO's Chernobyl (I used to write on a blog, in Spanish but Google Translator works quite well). Check it out here conexioncausal-wordpress-com.translate.goog/2019/06/23/chernobyl-reactores-vs-bombas-nucleares/?_x_tr_sl=es&_x_tr_tl=en&_x_tr_hl=en&_x_tr_pto=wapp
@@jkzeroI will definitely give it a read, thank you!
Great vid as always! but I have two questions to ask? The first one is in a nuclear device's initiator what type of neutrons is being produced slow or fast ones? The second one is when a atom got split what type of neutrons is produced slow or fast ones?
thanks for the comment and the questions, I love triggering more questions than providing answers. In this I can provide the answer to your questions: in both cases the neutrons are fast; which is no surprise; otherwise, they would not had been used. A bomb requires fast neutrons because the chain reaction is very fast, of the order of a micro-second, as calculated in the video "The Physics of a Nuclear Explosion." Slow neutrons are useless for a bomb because they are... well.. slow. Also, the secondary neutrons produces by fission are always fast, this is why a reactor needs a moderator as mentioned at the 08:13 mark.
@@jkzero thank you!, so in a nuclear device, the goal is to split the nuclei by not moderating the fast neutrons by using a moderator like graphite or water but by adding enough fissionable mass so at some distance after many cloisions the fast neutrons will be slowed and then it will be able to split the nuclei., if the density is increased too much k is more than one then the fission reaction is going to be exponential "explosive", is that right?
@@moodi6780 you got it, that is exactly right: in a bomb you want the chain reaction to go wild, a runaway reaction as fast as possible (this is why fast neutrons are needed) so the nuclear core is fissioned multiple times before it blows itself apart. Otherwise, you get a fizzle like the shot shown at the end of the video. In a reactor, on the other hand, the reaction is controlled by neutron absorbing materials but also the neutrons are slow so there. Important is that a reactor is NOT a controlled nuclear explosion, this is a classic misinterpretation. In a reactor there is no nuclear explosion because neutrons are slow and the uranium is not enriched.
Did you miss speak around 12:25, “fast neutron simply cannot produces a chain dreaction”? Your fizzle explanation is correct. However a bomb requires fast neutrons. This is all enrichment dependent for slow neutron.moderated power reactors. What about HEU reactors? What am I misunderstanding?
My bad. You are confining this analysis to LEU reactors. That’s implied in your statement. Sorry.
I see that I read your comment too late and you already figured it out.
Thank you for the informative video. I have 2 questions that I hope you could answer.
First is, which library did you use to obtain the values for the various cross sections?
Second, at 11:26, you wrote that lambda_f is the same for both fast and slow neutrons. Why is the fission mean free path the same for fast and slow neutrons? Thank you.
I’d be very interested in a comparison between U and Th cycle for civilian usage. There’re a lot of hype outside, that would be great to present the reality of each. And someday fast neutron reactors.
Thanks for bringing this up, I am aware of the hype around Thorium reactors and I have not been able to make up my mind on this but I could reach to some expert in the field. A few years back I was invited to a special meeting of nuclear scientists in Sicily. In the bus from the airport I met a guy and we began talking about nuclear reactors, he turned out to be Kirk Sorensen, one of the most vocal advocates for Thorium reactors. We spent a week in the island with other nuclear physicists, great guy. But after he convinced me that Thorium was the solution, he even gave me a copy of his PhD thesis, which I read completely; I am still not sure that Thorium solves all problems or if it solves problems that are not there. I will ask around for an update, I think this is a fascinating topic, I should probably read his thesis again.
Thorium fuel cycle is a pipe dream IMO:
1. Different chemical process for fuel production, so building completely new production chains is required.
2. Pa-233 has a huge half life - 27 days, which slows down refueling process and requires more safety control.
3. U-232. Makes operations with spent fuel almost impossible due to high-energy gamma-quants.
Tldr: MOX fuel for the win!
Another very interesting video! Thanks for the amazing content!
Glad you enjoyed it! Please like and share the love for nuclear physics
This is just such an awesome video
Thanks!
Yes. But isn't there a scale factor that needs to be taken into account? The bigger the bomb, and the lower its "density" the bigger the fast/slow neutron ratio effect on yield would be?
So is there a lower size limit below which you would actually want to use slow neutrons for a bomb?
Or is this size threshold just so far outside of buildable object sizes that it's not relevant?
Does this apply to the scenario in the sci-fi/horror film ALIENS, where the nuclear reactor of the colony on LV-126 was on a countdown to explosion? I can't remember if that was a fission or a fusion reactor . . .
I have not watched the film, I would need more context
Ah, now I see the side by side comparison of the fast and slow charts have different enrichment fraction scales. Would it be correct to say that commercial power reactors can not get into a high order nuclear explosion because, (1) they do not have high enough enriched fuel, and (2) the reactor is so over moderated that a run away chain reaction (k >> 1) is not possible?
This is correct, you totally got it!
@@jkzero. THANK YOU. With regard to next generation, small modular reactors (SMR), core designers want to used higher enriched fuel, even HEU. So this can remove one safety constraint. But the fast neutrons may not be adequately moderated either. I am not clear the reactors are feasible for private commercial applications. I believe some military reactors operate on HEU. Perhaps you could do and introductory video on SMR core dynamics sometime. I would like to know how the fast neutrons know how to behave themselves. I know my question is not clear. I guess I’m asking how the HEU core can burn for a long time without refueling.
@@jkzero Conversely, it has been estimated that US Naval reactors may be enriched to above 90%; what is their chance of a nuclear detonation?
@@Joe_VanCleave good question, I am pretty ignorant about naval reactors, I focused on reactors for commercial power generation.
They still can never achieve critically as this is extremely difficult to do.
I loved this! Do you know any resource to learn more about nuclear reactors design and performance ?
I am glad that you found the video of interest. I am not very knowledgeable in reactor physics but in case you like to follow well-paced lectures I would recommend the MIT course
Introduction to Nuclear Engineering and Ionizing Radiation, all the materials are available online. The lectures are on RUclips and the instructor is excellent.
The Upshot-Knothole series of tests was notorious for its generation of fallout. The above-ground fizzle of Ruth surely generated considerable fallout.
The idea of a nuclear detonation fizzle makes me cringe with nervousness. I couldnt imagine the clean up or lasting actinides being spread all over the place.
The Brits did some truly irresponsible tests in Australia in the 50s and 60s that resulted in burning and dispersal of elements like Pu239.
8:22 whats' a moderator
as explained at 8:28, a moderator is a material that, when neutrons collide with it, neutrons slow down. Neutrons released by fission move very fast, then they collide with the material (moderator), and after the collision move slower.
After this video, a video about the TRIGA reactor pulses would be amazing.
A few years back I was invited to give a seminar at the University of Mainz, where they let me poke around their TRIGA reactor. I do not know much about TRIGA reactors other than, being research reactors, they allow you to see the most magnificent blue light that I have ever experienced: Cherenkov. I have a video on Cherenkov radiation in the to-do list.
Dr. Diaz I freely admit I am deficient in advanced mathematics, algebra just goes right by me. However once I discovered that I was born on the anniversary of the bombing of Nagasaki I have taken an interest in nuclear weapons and, as a side effect of that, nuclear reactors. I am finding your series fascinating even though I can't follow the theory completely. The one factor I do not recall you mentioning in this video is Plutonium production in reactors. To my mind it is theoretically possible to create enough Pu in a reactor to make a nuclear detonation but I also know that the geometry of the reactor, combined with the randomness of the distribution of the Pu would make this happening accidentally a practical impossibility. Also the Pu-240 content would make it an even less probable event.
You right about the possibility of plutonium production in nuclear reactors; however, plutonium requires very large amounts to be used for a bomb, in fact plutonium bombs are very complicated because they require a very fast compression of plutonium core and plutonium but be cleaned from other isotopes that ruin the explosive properties of Pu-239. This is not possible in a nuclear reactor.
most important video underpinning world politics in nuclear affairs
Thanks, glad you liked it. My problem when I attempt to address this important question is the fact that I can answer it with physics, but in the words of Leslie Knope: 'all I have on my side is facts and science... and people hate facts and science"
need more videos about nuclear fission please
Loved that the first law quoted was Betteridge’s 😉
yeah, I preferred to come clean right away
I’ve been teaching this premise for years. A nuclear power plant cannot end in a nuclear bomb explosion. The physics just doesn’t allow it to happen. The method used to fission atoms is completely different. Still, I’ve had people tell me I’m a complete nut, and I am 100% wrong. What is that old saying….”it’s hard to win an argument with a smart person. But it is damn near impossible to win an argument with an idiot.”
I get your point. For a long time I wanted to make this video. When someone says "a reactor is just a bomb under control" I say "show me the math, at least I can show you the math of the contrary"
I thought that U-235 could fission with slow neutrons. Has someone asked this question already?
yes, U-235 fissions with slow neutrons, this is explained at the 06:42 mark
I enjoy a lot your excellent channel, well done!
Speaking of the yield, you have to take into account the total mass of the nuclear material also, don't you? Since the uranium content in a nuclear reactor is around 3 orders of magnitudes larger than in a nuclear weapon, this compensates the inverse squared effect of the characteristic time between neutron collisions. This way you end with a yield ratio between a small weapon (utilizing fast neutrons) and a large reactor (utilizing slow neutrons) around 10^4-10^5, resulting in explosion energy in 100-1000 kgs in terms of high explosive equivalent instead of 0,1-1 kgs.
Sure, this is nowhere compared to nuclear weapons yield and can be produced with conventional explosives much easier.
Some say that the initial explosion at the infamous Chernobyl accident was a low-efficiency nuclear detonation, or rather, "fizzle". The claim is based on evidence examining the ruins of the reactor hall, position of the biological shields etc. Check out That Chernobyl Guy's video on this topic: ruclips.net/video/kuptYyKoDM4/видео.html
Done❤
To boil water... yes a part of the problem.
LWR (reactors used today) use water in a pressure tank.
Dangerous and expensive. like an old steam machine.
Reactors can howevever be built safe and a lot cheaper , not to mention at least 100 times more efficient, and with only 1/10 initial load. Waste without plutonium.
When the research was going well in the 1960s the project was cancelled .
Nixon in 1970.
An intence propaganda against nuclear energy began, telling a LWR could explode lika a bomb.
The most dangerous was the russian RBMK. They were lost in the nazi thinking making bombs and electricity at the same time.
Best reactors are MSR , totally safe with no reactor pressure vessel.
However ONLY Thorium can come in question as it can run in thermic neutron spectrum,
while uranium 235/238 can not.
Thanks for a god presentation on the physics of U238/U235/Pu239.
Yes, it can happen due to design flaws like in Tschernobyl or in other not so sophisticated reactors before.
you are describing a steam explosion, the video refers to nuclear explosions
Not sure what difference it makes, whether the explosion is "just" a steam explosion that blows the reactor apart, or a nuclear explosion that ... well, blows the reactor apart. What happened at Chernobyl was sufficiently bad, even if it was "only" a steam explosion.
I think there is a big difference because modern reactors have a massive containment building around them; therefore, a steam explosion will likely not damage the reactor components, and more importantly, to the surrounding area, making nuclear reactor extremely safe to live around. A full-scale nuclear explosion (which is not possible) would completely vaporize any containment around and produce catastrophic damage several kilometers around.
Chernobyl was a steam explosion, you are right, and it was terrible; however, the reactors there were designed to fail and didn't have containment buildings. No other nation in the world would have built such time bombs.
Usa did alot timebombs too, just every1 silent about it, u hypocryte shhteater.
Your definition is incorrect. A “fizzle” is a nuclear explosion that exploded below its design yield. However, *it is still a nuclear explosion*
The k value is still greater than 1 at the time of detonation but is unable to sustain for long enough to achieved its design yield before it blew itself apart and reduce k value to less than 1.
(If only the convention explosive detonate then they would described it exactly that… conventional explosive inside the bomb went but not a nuclear explosion)
So, yes a nuclear reactor like Chernobyl could definitely become a “fizzled” nuclear bomb accidentally as the design flaw which allows for positive void coefficient means that there is a possibility of a reactor runaway where power would continue to increase until it basically blew itself apart.
Hydrogen/steam explosion doesn’t vaporised 190 tonnes of uranium in a blink of an eye like magic… Chernobyl reactor 4 core was pretty much left emptied after the explosion. The famous “elephant foot” is actually over 90% melted sand with only traces of fission products in it) and all evidences points towards very little of the reactor core are left onsite. (Note Chernobyl reactor cores are gigantic)
They were able to sent people right inside the Chernobyl reactor just several months after the explosion… compare to Fukushima which they still can’t get anybody near the reactor after 12 years.
In answer to the clickbait, yes. Several have, deliberately or unintentionally.
SL/1, SPERT, BORAX and Chernobyl no. 4 all suffered steam explosions.
At Fukushima, hydrogen was generated by the hydrolysis of the zirconium cladding, and that exploded.
None of these were nuclear explosions, but they were nevertheless explosions.
Nuclear reactors can become dirty nuclear bombs , as Chernobyl and Fukushima demonstrated. Wouldn’t you agree Dr. Diaz ?
Under dramatic conditions, nuclear reactor can be taken to critical scenarios. In Chernobyl the most important factors were the terrible design, bad operation, and lack of containment that led to a a run-away reaction and the subsequent stem explosion. Not a nuclear explosion.
Fukushima was different, reactors cores melted down but the explosions were just hydrogen explosions, nothing nuclear either.
It may not be practical, but apparently even 20% HEU can be used to create a nuclear explosion.
I am not aware of this, if there is anything to be corrected on the video I would include an errata, could you share any reference about this explosion from low-enriched uranium? Thanks
@@jkzero Figure 3.1 from this ORNL technical report shows finite critical masses for a bare sphere when the concentration of U-235 is above 5.4%.
web.archive.org/web/20131102011417/web.ornl.gov/info/reports/1998/3445606060721.pdf
They can and HAVE exploded. But they can't explode like a nuclear bomb.
That is precisely the thesis of the video.
😮
Can it explode like a nuclear bomb, with a classic mushroom cloud .... No. But that is a false question, and a misdirection.
Can a nuclear reactor suffer an in-core nuclear detonation leading to rapid catastrophic disassembly and release. Yes, in some circumstances. It has already happened at least three times, and arguably several or many more. SL-1, KIWI-TNT, and Chernobyl all suffered in-core nuclear detonations and disassemblies. The assemblies could not release more than tens to a hundred tons of TNT equivalent release from prompt fission yield. But tens of tons is certainly enough to utterly destroy the reactor and any containment.
Many of the tiny SNAP and SPERT reactors may have crossed that threshold as well.
Is this a serious concern for nuclear reactors? Yes. The reactors must be designed and operated in such ways that it is not possible to achieve prompt criticality leading to disassembly (or even serious damage) under any conceivable incident scenario - including especially hostile action by any adversary - internal or external, and from any conceivable accident scenario. It is not enough that the probabilities be low. The consequences are far too severe to allow any such scenarios.
This also extends to spent fuel pools and other fissile material storage.
The topic of the video is the fact that a nuclear reactor cannot explode like a nuclear bomb (which stated within the first 20 seconds of the video to avoid misleading viewers), and the title of the video makes clear that this is a comparison of the nuclear reactions taking place in a reactor and how they differ from those in a bomb. Other types of explosions are mentioned at 6:24.
@@jkzero Ah - but that is precisely the misdirection that will mislead viewers, as the viewers are mostly not well versed in nuclear physics or even the consequences of catastrophic malfunctions in such facilities. In many ways the consequences of a lower yield nuclear detonation in-core that destroys the reactor and facility and spreads enormous quantities of radioactive material across the landscape and into the atmosphere is worse. These are potentially nation killing events. Arguably, Chernobyl ended the USSR. Fukushima nearly did the same to Japan, though no in-core detonation occurred there.
If such an event occurred in a US reactor in the midwest, it would wipe out much of the US heartlands ability to produce food (both as crops and animals). Farther east and the population impacts are massively larger, but with lower food production impacts.
Many of the reactors are embrittled or have extremely questionable primary vessels already, making them more vulnerable to catastrophic failure. Nearly all of them are extremely old making them more vulnerable yet, with embrittlement of all of the nozzles and connections.
Some like CGS in Washington State have other serious issues. NRC has allowed CGS to run with a broken bracket on a primary ejector pump in the primary vessel by running with a richly hydrogen environment to reduce oxidative damage to the remaining bracket, and greatly increasing the risk of a catastrophic failure.
The nuclear ago of fission is over. It is highly non-economical, and hugely risky, with no path to deal with the long lived radioactive wastes or fissile materials or other actinides. It's time is done. But the industry refuses to go quietly into history.
Also, the comment of other explosions at 6:24 is inadequate. We HAVE observed in-core detonations.
In all three that I cited, the reactors were driven deep into prompt criticality.
SL-1 was a far over powered reactor. When it was designed the 1 stuck cold rod criteria did not yet exist. SL-1 led to that criteria. When an operator overcoming the jamming of a control against poison cladding, added to reduce the reactors power level, jerked the central control blade nearly two feet upward, he inadvertently set the stage for a prompt critical rise through 25 generations of power rise reaching enormous power levels before the flash vaporization of the coolant, and fuel led to reactor disassembly ending the excursion. But the rectors destruction was already guaranteed by that time.
KIWI-TNT was intentionally destroyed by overriding safety criteria, and snap moving the control element far beyond design. That resulted in a similar catastrophic prompt nuclear rise and detonation destroying the reactor.
Chernobyl similarly was destroyed by horrifically bad design and horrifically bad operation. The control rods were tipped with graphite that increased reactivity before the nuclear poisons could enter the core. The reactor was then run in a highly unstable regime at low power with xenon build up being overcome by withdrawing all of the control rods. When power rise then began the chief operator order activation of AZ-5 - a full scram - which then enormously added to the reactivity of the reactor and causing a prompt nuclear power rise to levels vastly greater than the reactor could ever handle.
In all three cases the result was precisely what the video argues cannot happen - a prompt critical nuclear chain reaction far above unity, resulting in a catastrophic sub millisecond period and a power rise that screamed through the power range and beyond, generating ton to 30 ton TNT equivalent energy yields that vaporized the central core and splattered the rest outward before the negative reactivity insertion was great enough to shutdown the reaction. Even then, delayed neutron generation drove things even higher yet.
This is precisely what the vide argues cannot happen. But it did. It did precisely that. By definition these were nuclear detonations, albeit very low yield in bomb terms. But the yield doesn't need to be in the kiloton range to utterly destroy a reactor. And As I noted before, the consequences of destroying the reactor facility are in many ways worse that a full bomb yield detonation.
Also, the fizzles mentioned have to be remembered are typically 500 ton yield detonations. Those are enormous detonations even as failures as nuclear bombs or devices.
Add to these the many SNAP and SPERT reactors tested to failure by ejecting control elements. Many of these disassembled as a consequence. These were even lower yield nuclear detonations, with low consequence other than to the tiny reactors themselves.
The Godiva criticality accident took that a step lower yet, achieving a prompt criticality but not destroying the assembly.
The various TRIGA reactors operate in that regime - triggering short lived low Keff prompt criticalities of insufficient power to damage the reactors.
@@tunneloflight I understand you point now, I think you are right. However, using your comment " the viewers are mostly not well versed in nuclear physics," when they hear "nuclear explosion" they all think on a full-scale at-least Hiroshima-like devastation and not the in-core detonation that you describe. But I get your point, thanks for sharing that.
Jadajadajda how about bn-800 type reactors?
Ur knowledge severly outdated
Chernoble and fukushima were nuclear explosions looking inside the fukushima reactor core. Nothing was left of the fuel rods as was the same at Chernoble, in a 1950,s book i read that a nuclear pile will explode with the force of tnt if left to run away.
That's factually wrong. Both were hydrogen explosions. The fuel reached such temperatures that the water in the core turned into hydrogen gas, which ignited. In the case of chernobyl, the entire plant blew up, including SOME of the fuel. The rest continued to react and melt through the bottom of the reaction chamber, forming the famous elephants foot. The same happened in fukushima to a much lesser degree, because the plants were built to withstand such a blast.
Ask di- ichi.
Claiming a reactor cannot create an atomic explosions is questionable, especially if we include the waste in the pool (which all reactors should have) . If that pool looses it's water, we can get a critical mass and kaboom.
in the video I show all the calculations that show that a nuclear explosion is not possible, if you could share the equivalent calculation describing how a nuclear explosion can occur with reactor waste I would love to learn.
@@jkzero look like I am not allowed to paste links, The subject of criticality is well understood, Plenty of videos explain it good. Not here to pick a fight but if someone throw maths claiming criticality cannot occurs in or around a nuclear reactor, especially when most authorities on the subject say otherwise, it is hard not to feel an attempt to be misled. As always I also embrace the possibility of being completely wrong. Friendly yours...
Criticality leads to heat and the amount of heat down to the concentration of fiscal material. In a bomb that a concentration is high enough to result in an explosion, in waste it just melts. Two completely different things.
@@bluebirdfan100 totally agree
@pierregrondin4273 Criticality is always needed for a sustained nuclear reaction. But this is not the same thing as an explosion.
Bravo. Just one of the best channels on RUclips
Appreciate that, I just ask to support the channel by liking and sharing so the mighty algorithm can find more people interested in these fascinating topics.