Congratulations to David LeBlanc (ORNL)

[Kurt Sellner]

What problem does IMSR uniquely solve that is distinct from LFTR?

Well, I feel a bit like I've been backed into a corner. Rather than speak for Dr. LeBlanc I'll let him speak for himself. I found some of his words in this article I was able to find with a bit of searching the internet.

http://www.daretothink.org/msr-developm ... amms/imsr/

And finally, still according to LeBlanc, a burner has negligible fuel costs, has assured and abundant resources – notably low enriched uranium – is much simpler in design, can be realized with lower R&D-costs and lower capital costs.

It should be obvious that Dr. LeBlanc thinks he has something to offer that LFTR cannot otherwise if people asked him about MSRs then he'd just give them your phone number, does that sound about right Mr. Sorensen?

Maybe the problem that IMSR solves is just that Terrestrial Energy is in Canada while Flibe Energy is in the USA. Laws on importing and exporting nuclear technology does come into the decision on what kind of power plant to build. It almost hurts to think that a lesser technology would "win" over something so mundane but that's the world we live in.

[TerjeP]

Arguably the advantage of the IMSR is speed to market. Though obviously that is speculative at this point in time. Ultimately it depends how many technical and regulatory hurdles there are to overcome and which of the two design teams can most quickly overcome the hurdles applicable to their design.

Setting aside speed to market I think that most people envisage that the LFTR, once licensed and commercialised, will be a superior product.

If Flibe Energy, or anybody else can address the speed to market question then I expect the LFTR would win back some buzz that the IMSR now enjoys. Whether that buzz is useful at this point is time is another matter.

[macpacheco]

Arguably the advantage of the IMSR is speed to market. Though obviously that is speculative at this point in time. Ultimately it depends how many technical and regulatory hurdles there are to overcome and which of the two design teams can most quickly overcome the hurdles applicable to their design.

Setting aside speed to market I think that most people envisage that the LFTR, once licensed and commercialised, will be a superior product.

If Flibe Energy, or anybody else can address the speed to market question then I expect the LFTR would win back some buzz that the IMSR now enjoys. Whether that buzz is useful at this point is time is another matter.

If IMSR and/or ThorCon achieve their performance and cost goals (big if), I think the justification for LFTR might not justify itself.
Think about it, IMSR promises to use 1/6th as much Uranium at a lower enrichment level on a 7 year cycle with once through fuel.
Reprocess IMSR spent fuel and it might be possible to achieve 1/8th to 1/10th as much mined Uranium as current reactors.
ThorCon should achieve even better Uranium economy due to lots of Thorium mixed in, perhaps <1/10th as much Uranium needs without reprocessing and even better with.
In either reactor if they perform as advertised, with reprocessing spent fuel and other wastes should be less than 10% of current reactors.

I say that, because LFTR is likely to cost substantially more due to extra online reprocessing facilities required for breeding. Even 50% more expensive total operating costs could be enough to make it a niche reactor only for countries with limited Uranium supplies (and restrictions of Uranium importing) like India. If a reactor uses 10% as much raw Uranium as a PWR/BWR, Uranium prices become a drop in the bucket type of cost.

[Kirk Sorensen]

Think about it, IMSR promises to use 1/6th as much Uranium at a lower enrichment level on a 7 year cycle with once through fuel.

That may be what they are promising, but they're heading for a Transatomic-class embarrassment in that case. 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.

I say that, because LFTR is likely to cost substantially more due to extra online reprocessing facilities required for breeding.

You're also assuming that waste costs nothing. That is a very bad assumption. Waste issues are PREVENTING many nations from considering any form of "once-through" nuclear power at present, because many countries that would like to have nuclear power have no desire to go through the hell they've seen Western countries pursue as they seek somewhere to put the waste. IMSR does nothing for the waste problem, and in all likelihood makes it even worse than PWR.

[TerjeP]

That may be what they are promising, but they're heading for a Transatomic-class embarrassment in that case.

It very clearly is what they have promised. Not in a binding promise but in all their promotional activity. You seem to be suggesting they are stupid or dishonest.

[jon]

'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 ?

[macpacheco]

'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.

[jagdish]

Any MSR will have the advantage of Xe escape from liquid fuel. It is going to be more fissile economic. Thorium produces superior U-233 and it gives better economy of fissile. The cost is higher initial fissile feed. Terrestrial design will have its advantages and disadvantages. The prize is first past the post as working MSR.
Once the experience of working MSR is gained, someone will come up with a fast breeder of MSR type. As things stand, only Russia, India and China are wholeheartedly working on solid fuel fast reactors. Many have fallen on wayside.

[TerjeP]

Enrichment of reload fuel at equilibrium
2-3% for start-up, 5-19% makeup fuel

Taken from the table on page 14 of the following document.

https://aris.iaea.org/PDF/IMSR400.pdf

My take on this is that over time the added fuel needs to be at a higher enrichment level to ensure that the reactor can remain critical. Or remain critical at the relevant temperature and power levels.

My understanding is that 19% enrichment is still considered LEU. But it's definitely at the high end of the range.

[Kirk Sorensen]

If you're running an MSR on greater than 5% enriched uranium fuel, you're running it on HEU. The only difference being that the government downblended it before you got it, and then you downblend it even further.

Commercial enrichment facilities don't make enrichments greater than 5%. Governments make it from HEU.

[jon]

'Commercial enrichment facilities don't make enrichments greater than 5%. Governments make it from HEU.'
Speaking of which, did anything happen to the US government's U233 stocks ?

[jagdish]

Some governments have RG plutonium which is being used or planned to be used for MOX fuel. It could be used for initial fissile feed or make up fissile in later stages.

[E Ireland]

If you're running an MSR on greater than 5% enriched uranium fuel, you're running it on HEU. The only difference being that the government downblended it before you got it, and then you downblend it even further.

Commercial enrichment facilities don't make enrichments greater than 5%. Governments make it from HEU.

Georges Besse II is built for 8% IIRC.
EDF has been chomping at the bit to get the French regulator to approve higher enrichments for its PWR fleet so that it can extend burnups further.

[TerjeP]

Kirk - I must admit that you have taken some of the gloss off the IMSR design. I am now plagued by questions about their fuel cycle.

[Kurt Sellner]

If you're running an MSR on greater than 5% enriched uranium fuel, you're running it on HEU. The only difference being that the government downblended it before you got it, and then you downblend it even further.

Is that a complaint against Terrestrial's IMSR or against the current enriched uranium industry?

Commercial enrichment facilities don't make enrichments greater than 5%. Governments make it from HEU.

What is preventing commercial enrichment facilities from producing 5% U-235? If there is a legal restriction then while we lobby the government for regulations that allow MSRs to get built then we should also lobby for a rule change to allow the production of the fuel needed for them. If it's a matter of not having a market for 5% U-235 that keeps commercial enrichment from producing it then the problem solves itself with the construction of reactors that will need it as fuel.

The lack of commercial 5% enriched uranium production shouldn't count against IMSR any more than a lack of commercial thorium production should count against LFTR.