4 ms·

Yeah, I missed it the first time. You commented when I started editing it. I took (N,TOT) this time. Fission product cross sections is still higher. https://img

Yeah, I missed it the first time. You commented when I started editing it. I took (N,TOT) this time. Fission product cross sections is still higher. https://imgur.com/a/pjoNv1p https://imgur.com/a/pjoNv1p CANDU: DUPIC fuel cycle is not demonstrated. Canadians don't run PWRs. India, China and South Korea run PWR and CANDU, not much advanced R&D in India. Chinese CANDU in Qinshan may be testing this. US is most advanced in nuclear R&D. Why not build a CANDU in the US and demonstrate this? I was talking about pressuriser and DNB. If there is no pressuriser (PWR) and constant adjustment of recirculation flow (BWR), clad may get damaged and fuel may melt because of DNB or denucleate boiling. Not inherently safe, engineered systems are needed. (In BWR fuel itself is engineered top-to-bottom with different enrichment levels and different burnable poison concentrations.) Control rod adjustments are needed till a xenon equilibrium is attained. Also flux flattening circus, boron dilution circus etc. Operators are needed to babysit a LWR or CANDU. This is not like diesel generator or PV panel. Passive shutdown does not mean passive operation like a diesel. I don't think first generation of MSRs can be like diesel generators. Operators are needed. But, there is potential for nuclear reactors to be like diesel generators with fluid-fuel reactors. (Edit: Reply to "Today, most CANDU's use ~2% enriched feed, I believe." No. ALL heavy water reactors run with natural uranium in most tubes, depleted uranium or thorium in few pressure tubes for flux flattening circus. No enriched uranium in any tubes.)

acidburnNSA 8y ago
Total includes scattering which isn't a loss mechanism. Best bet is to do a spectrum weighted 1-group macroscopic absorption XS (including all neutron loss mechanisms) in various reactors for a meaningful comparison. Most nuclear textbooks have these in the appendix. All I'm telling you is that boron is used for control in fast reactors. I think you asked how it was done a while back. I kept reading about all these advantages of "slightly enriched uranium" in candus so I'm surprised they aren't using it anywhere! [1] Autonomous control can theoretically be done with many kinds of reactors and fuels. Sodium reactors have vast pools of liquid metal with extraordinary thermal conductivity and heat capacity. Lead-cooled reactors are similar. So are salt-cooled FHRs, and pebble-bed gas reactors like x-energy. There are a few decades of regulatory catchup before that can happen. Arpa-e has a current project into operator assistance which is aiming to move to more autonomous control. Don't forget about maintenance costs. Equipment and chemistry will cause maintenance of any reactor to be higher than an average diesel. Fluid fuel will have 50% of the periodic table in thermal gradients, plating out in heat exchangers and other cold surfaces. Sodium reactors have sodium fires. Lead reactors have corrosion. Gas reactors have power cycle leaks. It's a worthy goal but we have lots of work before we get there. We don't have enough experience with fluid fuel yet to judge how maintenance of a commercial unit will pan out. It might be great, or it might prove difficult. Very worthy goal though! [1] https://inis.iaea.org/search/search.aspx?orig_q=RN:20038082 https://inis.iaea.org/search/search.aspx?orig_q=RN:20038082
- achalhp 8y ago
  RE "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)" As fission product concentration increases, even fast reactors have to remove fuel and reprocess it. What works for boron also works for fission products. I don't think any reactor (fast or thermal) can close fuel cycle without the help of reprocessing. May be fast reactors need less frequent reprocessing, that's it. (LWR-SNF cannot go fast critical. May be fission products is not removed, but reprocessing is needed to concentrate Pu in LWR-SNF.) Even if LWR-SNF has to be used as-is, it has to be toasted in blanket region of fast reactor before it is used as fuel. Some designs like TWR claim no reprocessing needed between toast step and burn step. I agree with that. But, for complete fission of SNF, fission-product removal is needed at some stage when fission product concentration exceeds a particular level in the fuel rod. No exception for travelling wave burnup. For a critical reactor core some minimum length of fuel rod is always required to be in use. If fission product starts accumulating from bottom of the fuel-rod towards top, somewhere at the midway core can't go critical because a minimum length of rod is needed for criticality. 4% of 1GW-LWR fuel runs for 4.5 years. 100% of this fuel has potential for 112.5 years. A solid-fuel rod can't maintain integrity for 100 years. The crystal structure damage can't be reversed by any amount of maintenance. This is the same phenomenon how solar panels get degraded in sunlight. A fuel rod has crystal structure damage by radiation as well as by fission products. Fluid-fuel can be used indefinite time and it is easy to reprocess liquid fuel by any method. There is no crystal structure to get damaged. ORNL was working on physical separation of fission products like vacuum distillation when the project was cancelled. Chemical separation and isotopic separation may raise proliferation concerns and they may not be environmentally friendly. There is a chemical separation of fuel from fission products called fluoride volatility, which is used in industrial scale for enrichment of fuel. But, it works only for fluoride salts. ORNL has demonstrated this process when they switched from U235 to U233. They irreversibly damaged the drain tanks and hastelloy plumbing by doing this. MSRE would have lasted longer if they had not done this fluorination experiment. RE "Fluid fuel will have 50% of the periodic table in thermal gradients, plating out in heat exchangers and other cold surfaces." Just throw away the hot leg plumbing and heat exchangers every 2.8 years initially (MSRE salt loop was circulated for 2.8 years) and increase this incrementally. Fact: In solid fuel reactors fuel itself acts as a primary heat exchanger. In 4.5 years LWRs throw away a heat exchanger worth of Zr tubes/cladding. Earlier LWRs threw away solid-fuel every 3 years. Why point fingers at MSR folks when solid-fuel reactors throw away stuff? Note the difference between Inconel 625 (similar to hastelloy-N) and Zr. https://www.tricormetals.com/cost-comparison.html https://www.tricormetals.com/cost-comparison.html

acidburnNSA 8y ago

Total includes scattering which isn't a loss mechanism. Best bet is to do a spectrum weighted 1-group macroscopic absorption XS (including all neutron loss mechanisms) in various reactors for a meaningful comparison. Most nuclear textbooks have these in the appendix. All I'm telling you is that boron is used for control in fast reactors. I think you asked how it was done a while back. I kept reading about all these advantages of "slightly enriched uranium" in candus so I'm surprised they aren't using it anywhere! [1] Autonomous control can theoretically be done with many kinds of reactors and fuels. Sodium reactors have vast pools of liquid metal with extraordinary thermal conductivity and heat capacity. Lead-cooled reactors are similar. So are salt-cooled FHRs, and pebble-bed gas reactors like x-energy. There are a few decades of regulatory catchup before that can happen. Arpa-e has a current project into operator assistance which is aiming to move to more autonomous control. Don't forget about maintenance costs. Equipment and chemistry will cause maintenance of any reactor to be higher than an average diesel. Fluid fuel will have 50% of the periodic table in thermal gradients, plating out in heat exchangers and other cold surfaces. Sodium reactors have sodium fires. Lead reactors have corrosion. Gas reactors have power cycle leaks. It's a worthy goal but we have lots of work before we get there. We don't have enough experience with fluid fuel yet to judge how maintenance of a commercial unit will pan out. It might be great, or it might prove difficult. Very worthy goal though! [1] https://inis.iaea.org/search/search.aspx?orig_q=RN:20038082 https://inis.iaea.org/search/search.aspx?orig_q=RN:20038082

achalhp 8y ago
RE "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)" As fission product concentration increases, even fast reactors have to remove fuel and reprocess it. What works for boron also works for fission products. I don't think any reactor (fast or thermal) can close fuel cycle without the help of reprocessing. May be fast reactors need less frequent reprocessing, that's it. (LWR-SNF cannot go fast critical. May be fission products is not removed, but reprocessing is needed to concentrate Pu in LWR-SNF.) Even if LWR-SNF has to be used as-is, it has to be toasted in blanket region of fast reactor before it is used as fuel. Some designs like TWR claim no reprocessing needed between toast step and burn step. I agree with that. But, for complete fission of SNF, fission-product removal is needed at some stage when fission product concentration exceeds a particular level in the fuel rod. No exception for travelling wave burnup. For a critical reactor core some minimum length of fuel rod is always required to be in use. If fission product starts accumulating from bottom of the fuel-rod towards top, somewhere at the midway core can't go critical because a minimum length of rod is needed for criticality. 4% of 1GW-LWR fuel runs for 4.5 years. 100% of this fuel has potential for 112.5 years. A solid-fuel rod can't maintain integrity for 100 years. The crystal structure damage can't be reversed by any amount of maintenance. This is the same phenomenon how solar panels get degraded in sunlight. A fuel rod has crystal structure damage by radiation as well as by fission products. Fluid-fuel can be used indefinite time and it is easy to reprocess liquid fuel by any method. There is no crystal structure to get damaged. ORNL was working on physical separation of fission products like vacuum distillation when the project was cancelled. Chemical separation and isotopic separation may raise proliferation concerns and they may not be environmentally friendly. There is a chemical separation of fuel from fission products called fluoride volatility, which is used in industrial scale for enrichment of fuel. But, it works only for fluoride salts. ORNL has demonstrated this process when they switched from U235 to U233. They irreversibly damaged the drain tanks and hastelloy plumbing by doing this. MSRE would have lasted longer if they had not done this fluorination experiment. RE "Fluid fuel will have 50% of the periodic table in thermal gradients, plating out in heat exchangers and other cold surfaces." Just throw away the hot leg plumbing and heat exchangers every 2.8 years initially (MSRE salt loop was circulated for 2.8 years) and increase this incrementally. Fact: In solid fuel reactors fuel itself acts as a primary heat exchanger. In 4.5 years LWRs throw away a heat exchanger worth of Zr tubes/cladding. Earlier LWRs threw away solid-fuel every 3 years. Why point fingers at MSR folks when solid-fuel reactors throw away stuff? Note the difference between Inconel 625 (similar to hastelloy-N) and Zr. https://www.tricormetals.com/cost-comparison.html https://www.tricormetals.com/cost-comparison.html