jon wrote:'What I am hearing from those that have evaluated their system is perhaps a 10% improvement in uranium utilization over today's PWRs, and likely inferior fuel performance relative to CANDUs.'
They should get about a forty percent improvement in efficiency from hotter steam ( ~ 33% to 45% ), and, although they will probably use higher enrichment than PWRs, they leave the fuel in for seven years, instead of one and a half. Also they bubble out the xenon, so should get a better return on their neutrons. Aren't those similar advantages as from a LFTR ? Or does the U238 embuggerise things ?
That's not what they said. They stated they would get a total 6 fold improvement in mined uranium required MWh produced, even removing the hotter steam advantage that's still about 4x better burnup.
Dr LeBlanc NEVER said IMSR could need higher enrichment than PWR/BWR, in fact he stated enrichment levels as low as below 2% might be possible !
Which makes sense, cause:
Online fuel top offs = reactor starts with days, weeks (but probably not months) worth of excess reactivity (for instance ThorCon requires daily fuel top offs), PWR/BWR starts with years worth of excess reactivity at full power
Xe135/Kr is removed online = less neutron losses, this also reduces the need for extra fuel to overpower Xenon peaks (which produce excess neutrons outside of the peaks which then must be wasted/absorbed with control rods)
Graphite is a better moderator than water = less neutron losses
MSRs don't have a problem with too much Am/Cu in the fuel, with burnup cycles as high as 3x a normal PWR/BWR, a heck of a lot more Pu breeding and Pu fission takes place.
Lower neutron losses = More neutrons to convert Th232 into U233 and U238 into Pu239 and more neutrons to fission those later, which requires a lower fissile top off fuel
The much lower excess reactivity means the reactor has no intentional neutrons going to waste (control rod is purely a safety feature and is kept fully out in normal conditions)
I don't understand how any MSR could be just 10% better than PWR, perhaps the salt/coolant choice like pure NaF instead of LiF due to Tritium control.
If that's the issue, it doesn't forbid them from having a version 2.0 later with better salt/coolant choice.
If this makes the first IMSRs really cheap to operate that could generate a large volume of orders which will give them lots of capital for follow on improvements.
Not to mention they shied from Thorium cause 19% enriched U235 is hard to obtain and expensive (plus other issues), but they can revise that in future models.
LFTR is the extreme case where it can make a little more U233 than it consumes, so it should be able to achieve 100% burnup.
Finally, IMSR spent fuel is extremely attractive for reprocessing, as reprocessing for MSRs can be as simple as separating fission products from the rest (salt+fissile+fertile elements), mixing in just enough fissile+fertile to achieve the right fissile to fertile content and total nuclear fuel vs salt content and your ready to reuse the fuel (assuming the reprocessing process is also a molten salt process, such as pyro reprocessing). ALL plutonium, uranium, americium, curium, neptunium, thorium is recycled until fully fissioned or escapes as impurity mixed with fission products. A properly designed off gas system removes up to 40% of fission products online (as 40% of fission products either end up as Xenon or Krypton or temporarily become Xenon or Krypton then decay into something else).
Contrast that with PWR/BWR reprocessing...
1 - Open up small individual fuel pins, convert solid oxide fuel into some sort of liquid
2 - Separate fission products from Uranium from Plutonium from other fissiles/fertiles
3 - Uranium that comes out of reprocessing is re-enriched (if enough U235 content is present)
4 - Plutonium must be made into MOX
5 - Am/Cu/Np (aka minor actinides) must be stored unless a fast reactor is available to fission them
6 - Elements that will actually be recycled must be once again be made into solid oxide fuel
Its a comparison so unfair, that its more just to assume all MSR spent fuel will be reprocessed, while PWR/BWR fuel wont.
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