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> According to Gurri, modern information technology enables the public, composed of amateurs, to break the power hierarchies of the industrial age. This is rea

> According to Gurri, modern information technology enables the public, composed of amateurs, to break the power hierarchies of the industrial age. This is really reflected in my area: nuclear design. This has gone from once the most secret and guarded information possible (Manhattan project) to a world where there are 50 small companies working on various types of reactor designs [1], many run by what can easily be considered amateurs. Last week I was in D.C. at an industry conference and met a guy running one of these companies. He was explaining to me the merits of his design and had the basic physics unequivocally backwards. I prodded him gently on it: "Oh, you mean the fast neutrons don't get readily absorbed in fission products, not the slow ones, right?" He doubled down. Some poor schmuck is funding this guy. Meanwhile, Transatomic, the famed Thiel-backed molten salt company recently folded [2] partly because the two MIT grad student co-founders apparently spent more time giving TED talks about how thermal-neutron reactors could "run on nuclear waste" than reading the 1940s literature that established that this was not possible [3]. (To be fair to the co-founders who are wonderful and smart people, many reactor companies make big mistakes early on, most are just a lot less public about it) On the other hand, a then-amateur reactor designer named Kirk Sorensen read some stuff about molten salt reactors in an old book and then almost single-handedly built up an internet army of thousands of people yelling from the rooftops the benefits of fluid-fueled reactors. Now the big institutions like national labs have caught back up and there's serious talk and work on these reactors all over. Molten salt reactors (especially thorium-fueled ones) essentially went viral. So there's a lot of good and bad coming out of all this, and I'm not sure where it will end up. One thing from the article seems certain: we need new forms of accreditation. We should try to find ways to bring trust back to the situation given its new reality. [1] https://www.thirdway.org/infographic/the-advanced-nuclear-industry-2016-update https://www.thirdway.org/infographic/the-advanced-nuclear-in... [2] https://www.greentechmedia.com/articles/read/transatomic-to-shutter-its-nuclear-reactor-plans-make-its-technology-public https://www.greentechmedia.com/articles/read/transatomic-to-... [3] https://www.technologyreview.com/s/603731/nuclear-energy-startup-transatomic-backtracks-on-key-promises/ https://www.technologyreview.com/s/603731/nuclear-energy-sta...

achalhp 8y ago
What applies for fission products should also apply for control rods in fast spectrum. If control rods do not absorb fast neutrons, how a fast reactor is controlled? The cross section of fuel in fast spectrum also decreases. Fast reactors have larger fissile holdup. For every atom of fission fragment there are more fuel atoms in fast reactor than in thermal reactor. Fast reactors can run longer because fission products are dilute in the fuel. But, reprocessing is needed even for fast reactors to close the fuel cycle. The advantages like U238 or Pu239 fission or fast fission factor can be also obtained in heterogeneous thermal spectrum reactors. (Example: A CANDU is heterogeneous reactor. It can burn more plutonium and it can use LWR SNF-fuel without reprocessing.) For a fluid-fuel reactor the fuel acts only as fuel and heat exchange takes place outside reactor core. Fuel region in a fluid-fuel reactor can be as thick as it is needed. So, reactor can be designed for maximum multiplication factor. (Solid fuel rods can't be very thick, because they are also heat exchangers.) Slide 6 in this presentation. http://www.thoriumenergyworld.com/uploads/6/9/8/7/69878937/seaborg_technologies_thec18_slides.pdf http://www.thoriumenergyworld.com/uploads/6/9/8/7/69878937/s... Edit: This is a reply for: "I prodded him gently on it: "Oh, you mean the fast neutrons don't get readily absorbed in fission products, not the slow ones, right?" He doubled down. Some poor schmuck is funding this guy."
- acidburnNSA 8y ago
  Similar to fission products, neutron control material (like Boron) indeed does not absorb fast neutrons as much. Fortunately it still does absorb fast neutrons enough to control fast reactors (with which we have 430 reactor-years of experience or so). Indeed fast reactors need higher fissile concentration to be critical. Some kinds of fast reactors (like the Bill Gates Traveling Wave Reactor idea, which, disclaimer: I have professional connections to) can breed up plutonium in spent fuel and then burn it down without reprocessing (to be fair, the spent fuel would have to be hot refabricated into metallic fuel first, but that's still not separations/reprocessing). This kind of reactor needs enrichment once (to start up) and then can just be fed natural, DU, or SNF and it will run on a stream of it happily "forever" (until the vessel life is reached, at which point you transfer the core to a new machine and keep on shuffling). Only fast neutron systems can do such a thing. The Fast Mixed-Spectrum Reactor idea of BNL in 1980 was similar. Many fast-neutron MSRs are the same. Fast fission is not all that's at play in a fast reactor. It's all about Eta (neutrons released vs. neutrons absorbed in fuel). In a fast reactor, it skyrockets around 0.5 - 1 MeV because of three different physical facts: neutrons released per fission goes up with fast incident neutrons, fission cross section stays flat for all actinides around this range, and capture cross sections drop off towards zero around this range. This is discussed on: https://whatisnuclear.com/fast-reactor.html#havingmore https://whatisnuclear.com/fast-reactor.html#havingmore Having extra neutrons around means you can afford to invest more in breeding fissile material, and only fast neutrons can get you to the point where reactivity is flat or increasing instead of decreasing as fission products are produced. The only exception is Thorium fuel cycle, where U-233 releases a lot of neutrons even with thermal neutron absorption. In that case you have to be removing the fission products as they are created with separations, and this basically is only practical with fluid fuel. This was the idea of the Molten Salt Breeder Reactor project of Oak Ridge in the late 1960s. With reprocessing, you can definitely re-concentrate the remaining fissile material and get a thermal reactor critical again to burn it. But you cannot meaningfully use the other actinides as fuel, which is the whole idea of "running on spent fuel". Regarding that slide deck, I love the idea of molten fuel in tubes. I investigated it heavily once upon a time, being super excited about it. I ran into the problem that while salt fuel mass densities are low, separating them out even more physically makes the fissile density annoyingly low, to the point that I couldn't get the reactor performance I wanted for my then target market. I still think this concept is very interesting so I hope these folks do well. They won't be extracting any non-fissile energy from SNF though until they replace that moderating fluid with something like lead, gas, or sodium and change their fuel salt to a chloride. CANDUs can't use straight-up SNF out of a LWR without first stripping out the fission products. They're an example of "burning down the fissile material even better" but not "extracting the 100x more energy from the fertile U238". BTW the safety example in that slide deck is a bit disingenuous by suggesting that traditional reactors are not physically stable. If you know those guys you might want to tell them. Overmoderation and Doppler and the NRC ensure that they are inherently stable at power. These things aren't like the F-22 or whatever, requiring active systems to stay in the air. The engineered safety systems are simply for removing decay heat, which can be done passively in Gen III+ plants and indefinitely in any Gen-IV plant.

achalhp 8y ago

What applies for fission products should also apply for control rods in fast spectrum. If control rods do not absorb fast neutrons, how a fast reactor is controlled? The cross section of fuel in fast spectrum also decreases. Fast reactors have larger fissile holdup. For every atom of fission fragment there are more fuel atoms in fast reactor than in thermal reactor. Fast reactors can run longer because fission products are dilute in the fuel. But, reprocessing is needed even for fast reactors to close the fuel cycle. The advantages like U238 or Pu239 fission or fast fission factor can be also obtained in heterogeneous thermal spectrum reactors. (Example: A CANDU is heterogeneous reactor. It can burn more plutonium and it can use LWR SNF-fuel without reprocessing.) For a fluid-fuel reactor the fuel acts only as fuel and heat exchange takes place outside reactor core. Fuel region in a fluid-fuel reactor can be as thick as it is needed. So, reactor can be designed for maximum multiplication factor. (Solid fuel rods can't be very thick, because they are also heat exchangers.) Slide 6 in this presentation. http://www.thoriumenergyworld.com/uploads/6/9/8/7/69878937/seaborg_technologies_thec18_slides.pdf http://www.thoriumenergyworld.com/uploads/6/9/8/7/69878937/s... Edit: This is a reply for: "I prodded him gently on it: "Oh, you mean the fast neutrons don't get readily absorbed in fission products, not the slow ones, right?" He doubled down. Some poor schmuck is funding this guy."

acidburnNSA 8y ago
Similar to fission products, neutron control material (like Boron) indeed does not absorb fast neutrons as much. Fortunately it still does absorb fast neutrons enough to control fast reactors (with which we have 430 reactor-years of experience or so). Indeed fast reactors need higher fissile concentration to be critical. Some kinds of fast reactors (like the Bill Gates Traveling Wave Reactor idea, which, disclaimer: I have professional connections to) can breed up plutonium in spent fuel and then burn it down without reprocessing (to be fair, the spent fuel would have to be hot refabricated into metallic fuel first, but that's still not separations/reprocessing). This kind of reactor needs enrichment once (to start up) and then can just be fed natural, DU, or SNF and it will run on a stream of it happily "forever" (until the vessel life is reached, at which point you transfer the core to a new machine and keep on shuffling). Only fast neutron systems can do such a thing. The Fast Mixed-Spectrum Reactor idea of BNL in 1980 was similar. Many fast-neutron MSRs are the same. Fast fission is not all that's at play in a fast reactor. It's all about Eta (neutrons released vs. neutrons absorbed in fuel). In a fast reactor, it skyrockets around 0.5 - 1 MeV because of three different physical facts: neutrons released per fission goes up with fast incident neutrons, fission cross section stays flat for all actinides around this range, and capture cross sections drop off towards zero around this range. This is discussed on: https://whatisnuclear.com/fast-reactor.html#havingmore https://whatisnuclear.com/fast-reactor.html#havingmore Having extra neutrons around means you can afford to invest more in breeding fissile material, and only fast neutrons can get you to the point where reactivity is flat or increasing instead of decreasing as fission products are produced. The only exception is Thorium fuel cycle, where U-233 releases a lot of neutrons even with thermal neutron absorption. In that case you have to be removing the fission products as they are created with separations, and this basically is only practical with fluid fuel. This was the idea of the Molten Salt Breeder Reactor project of Oak Ridge in the late 1960s. With reprocessing, you can definitely re-concentrate the remaining fissile material and get a thermal reactor critical again to burn it. But you cannot meaningfully use the other actinides as fuel, which is the whole idea of "running on spent fuel". Regarding that slide deck, I love the idea of molten fuel in tubes. I investigated it heavily once upon a time, being super excited about it. I ran into the problem that while salt fuel mass densities are low, separating them out even more physically makes the fissile density annoyingly low, to the point that I couldn't get the reactor performance I wanted for my then target market. I still think this concept is very interesting so I hope these folks do well. They won't be extracting any non-fissile energy from SNF though until they replace that moderating fluid with something like lead, gas, or sodium and change their fuel salt to a chloride. CANDUs can't use straight-up SNF out of a LWR without first stripping out the fission products. They're an example of "burning down the fissile material even better" but not "extracting the 100x more energy from the fertile U238". BTW the safety example in that slide deck is a bit disingenuous by suggesting that traditional reactors are not physically stable. If you know those guys you might want to tell them. Overmoderation and Doppler and the NRC ensure that they are inherently stable at power. These things aren't like the F-22 or whatever, requiring active systems to stay in the air. The engineered safety systems are simply for removing decay heat, which can be done passively in Gen III+ plants and indefinitely in any Gen-IV plant.