A New Nuclear Technology Discussion Thread

[paulfdietz]

I think lead-magnesium would be more acceptable in the west than lead-bismuth. The melting point (248.7 C) is above that of lead-bismuth (123.5 C) but below that of just lead (327.46 C).

The application where lead-based coolant would make the most sense would be in accelerator driven subcritical reactors. High energy proton beams (~1 GeV) produce copious neutrons by spallation in heavy metal targets, like lead. These neutrons would allow a reactor operate even when subcritical, which is desirable if it's burning higher actinides that have very low delayed neutron fractions.

These accelerator driven reactors have not seen much market interest; it's cheaper to just store waste isotopes like these rather than reprocess and try to destroy them.

 

[UserJoe]

I think lead-magnesium would be more acceptable in the west than lead-bismuth. The melting point (248.7 C) is above that of lead-bismuth (123.5 C) but below that of just lead (327.46 C).

The application where lead-based coolant would make the most sense would be in accelerator driven subcritical reactors. High energy proton beams (~1 GeV) produce copious neutrons by spallation in heavy metal targets, like lead. These neutrons would allow a reactor operate even when subcritical, which is desirable if it's burning higher actinides that have very low delayed neutron fractions.

These accelerator driven reactors have not seen much market interest; it's cheaper to just store waste isotopes like these rather than reprocess and try to destroy them.

There were two different efforts looking at that concept. The LANL accelerator transmutation of waste project was mostly focused on burning waste, but it would have also generated electricity. The Rubbia energy amplifier was focused on energy production using thorium. Both would have required some significant accelerator development to get the beam powers that are needed. The MYRRHA research reactor being built in Belgium could serve as a small-scale test bed for the ATW technology but that is not the primary purpose of the facility purpose.

 

[paulfdietz]

There were two different efforts looking at that concept. The LANL accelerator transmutation of waste project was mostly focused on burning waste, but it would have also generated electricity. The Rubbia energy amplifier was focused on energy production using thorium. Both would have required some significant accelerator development to get the beam powers that are needed. The MYRRHA research reactor being built in Belgium could serve as a small-scale test bed for the ATW technology but that is not the primary purpose of the facility purpose.

The justification of being able to use thorium as fuel is an example of a common flawed rationale for nuclear projects.

The problem with nuclear is not fuel availability, it's cost. And cost is dominated by the capital cost of the facilities. So increasing that capital cost in order to use cheaper fuel is bass-ackwards. One sees this in justifications for ordinary breeder reactors, molten salt reactors, fusion, and here with accelerator driven reactors.

This all dates back to the early part of the nuclear age, when uranium availability was seen as a critical issue and enrichment was very expensive. Lawrence even proposed high current linacs for accelerator driven breeders in the 1940s. Fusion was initially seen as a way to breed plutonium.

Naturally, utilities and other customers for such things have no interest in technically interesting ideas that don't address their actual needs.

 

[Ananke]

Higher abundance isn't the only reason to consider thorium. The waste stream is smaller (for a given thermal power), shorter lived (fewer transuranics, but more hot gamma emitters), and less suited to bomb production (iirc due to the plutonium isotope balance).

The first two points should be attractive to nuclear power station operators, but currently are not - because the future cost of dealing with fuel is perenially put off as a problem for someone else in the future. That is a choice that could be addressed by public policy - just as letting coal and gas power stations off the hook for the future costs of emitting vast amounts of carbon are a public chocie that could be changed.

If those externalities start being internalised again, the costs would change - although I lack the expertise to predict whether they would change enough to make thorium more attractive than Yet Another PWR (to whatever degree Yet Another PWR even is attractive).

This all dates back to the early part of the nuclear age, when uranium availability was seen as a critical issue and enrichment was very expensive.

Likewise with the British AGR programme: it was thought that the significantly higher thermal efficiency of the gas-cooled core along with the ability to handle much lower-enrichment fuel would be a very attractive export package... except it wasn't when it was discovered that uranium was really abundant. It was - still is! - technologically impressive, and the fuel was slightly cheaper, but not sufficiently so to justify the significantly greater construction costs.

 

[Megalodon]

Higher abundance isn't the only reason to consider thorium. The waste stream is smaller (for a given thermal power), shorter lived (fewer transuranics, but more hot gamma emitters), and less suited to bomb production (iirc due to the plutonium isotope balance).

All of that is feasible for a uranium fuel cycle with harder neutron spectrum. The plutonium isotope balance takes care of itself if you run on longer fueling cycles, which civilian power wants to do anyway. The only civilian reactors with a real proliferation risk are CANDU. Natural uranium, online fueling, tritium as a byproduct, if you'd deliberately designed them for nuclear breakout capability I'm not sure you'd do anything differently.

 

[UserJoe]

The justification of being able to use thorium as fuel is an example of a common flawed rationale for nuclear projects.

The problem with nuclear is not fuel availability, it's cost. And cost is dominated by the capital cost of the facilities. So increasing that capital cost in order to use cheaper fuel is bass-ackwards. One sees this in justifications for ordinary breeder reactors, molten salt reactors, fusion, and here with accelerator driven reactors.

This all dates back to the early part of the nuclear age, when uranium availability was seen as a critical issue and enrichment was very expensive. Lawrence even proposed high current linacs for accelerator driven breeders in the 1940s. Fusion was initially seen as a way to breed plutonium.

Naturally, utilities and other customers for such things have no interest in technically interesting ideas that don't address their actual needs.

The accelerator transmutation of waste project could be viewed as a possible alternative solution to long-term spent fuel disposal and maybe that will be revisited since that has ground to a halt in the US. It could all depend on the outcome of the recent supreme court case about temporary spent fuel storage facilities.

The seeming abundance of uranium is really a false sense of abundance because nuclear power did not grow around the world as expected. The supply is quite finite. It is really a bit more nuanced than that (as it always is) and comes down to how much is recoverable at a given price level. It is not an immediate issue. The immediate issue is increasing the extraction and enrichment of known resources to meet projected demand. Fuel supplies will be tightly constrained in the near future if that does not happen. The oceans have a lot of uranium, but it is expensive to extract it. Uranium is also not equally distributed around the earth. There are also countries that have good thorium reserves and don't have good uranium reserves. The other thing thorium could do is extend the length of fuel cycles without increasing enrichment. Current LWR end of life fuel bundles get half of their power from plutonium fission. Heavy water and graphite moderated reactors would be in the best position to take advantage of thorium.

The latest Red Book about world uranium supplies was published recently by the OECD Nuclear Energy Agency if anyone is interested in more than you probably want to know about the details of uranium supplies and reserves.

 

[paulfdietz]

The accelerator transmutation of waste project could be viewed as a possible alternative solution to long-term spent fuel disposal and maybe that will be revisited since that has ground to a halt in the US. It could all depend on the outcome of the recent supreme court case about temporary spent fuel storage facilities.

The seeming abundance of uranium is really a false sense of abundance because nuclear power did not grow around the world as expected. The supply is quite finite. It is really a bit more nuanced than that (as it always is) and comes down to how much is recoverable at a given price level. It is not an immediate issue. The immediate issue is increasing the extraction and enrichment of known resources to meet projected demand. Fuel supplies will be tightly constrained in the near future if that does not happen. The oceans have a lot of uranium, but it is expensive to extract it. Uranium is also not equally distributed around the earth. There are also countries that have good thorium reserves and don't have good uranium reserves. The other thing thorium could do is extend the length of fuel cycles without increasing enrichment. Current LWR end of life fuel bundles get half of their power from plutonium fission. Heavy water and graphite moderated reactors would be in the best position to take advantage of thorium.

The latest Red Book about world uranium supplies was published recently by the OECD Nuclear Energy Agency if anyone is interested in more than you probably want to know about the details of uranium supplies and reserves.

There are two issues discussed here; let me address them in turn.

The waste disposal argument founders on the issue of cost. Sure, ADW (accelerator destruction of waste) is possible. But simply storing spent fuel is very cheap. It turns out that one reduces the net present value of the cost of dealing with the waste by procrastinating. Waiting 20 years and doing ADW then will be cheaper (with realistic values for interest rates) vs. doing it now. Waiting 40 years will be even cheaper. And so on, forever.

The only good argument would be if the waste decays so much that it would stop being self-protecting against amateur diversion of plutonium. But that would take ~300 years. There is no sense investing in ADW now if the only realistic market is three centuries in the future.

As for uranium cost increases... this can only make breeding competitive with burners in that high cost uranium environment. It can never make breeding competitive with nuclear power today. It's a way to limit damage to nuclear power from uranium cost increases, not a way to make nuclear more competitive with non-nuclear energy sources.

 

[Megalodon]

The only good argument would be if the waste decays so much that it would stop being self-protecting against amateur diversion of plutonium. But that would take ~300 years. There is no sense investing in ADW now if the only realistic market is three centuries in the future.

Not clear to me there's any need to worry about diversion of plutonium from civilian power waste, in that civilian power cycles are long enough to create an unacceptable Pu240 fraction for weapons use, and enrichment of plutonium impractical. I think this can be profitably ignored in perpetuity.

I think for purposes of proliferation risk from civilian reactors the big issue is CANDUs. Online fueling make these probably the best civilian reactor for a breakout weapons program.

As for uranium cost increases... this can only make breeding competitive with burners in that high cost uranium environment. It can never make breeding competitive with nuclear power today. It's a way to limit damage to nuclear power from uranium cost increases, not a way to make nuclear more competitive with non-nuclear energy sources.

I think there's a certain amount of conflation going on between breeders for waste management and breeders for fuel scarcity. If breeders can burn all their actinides the waste volume is reduced by ~2 orders of magnitude and only dangerous for a few centuries. That's desirable as far as it goes. But I agree with you that waste isn't a real problem and breeders aren't an economical fix.

 

[Tom the Melaniephile]

All of that is feasible for a uranium fuel cycle with harder neutron spectrum. The plutonium isotope balance takes care of itself if you run on longer fueling cycles, which civilian power wants to do anyway. The only civilian reactors with a real proliferation risk are CANDU. Natural uranium, online fueling, tritium as a byproduct, if you'd deliberately designed them for nuclear breakout capability I'm not sure you'd do anything differently.

And CANDU can also run on Thorium...

 

[Megalodon]

And CANDU can also run on Thorium...

Not really? Or to a limited extent anyway. I don't believe a break-even breeding ratio is possible with thorium in a thermal neutron reactor. You'll always need to bring in uranium or something else to support the reaction.