Tuesday, August 31, 2010

Advanced High Temperature Reactor

Barry Brook has a post + discussion on the Molten Salt - Advanced High Temperature Reactor, a joint UC Burkley-ORNL project. The Reactor is a Molten Salt-Pebble Bed Hybrid. Barry has some interesting comments, including telling observations. To a significant extent, Barry's views are shaped by the IFR crew including George Stanford, Jan Van Earp and Dan Meneley. These are all smart guys, but with a somewhat narrow perspective. Per Peterson appears to have a comfortable relationship with the IFR crowd, but they have different horses in the race. Barry explains pee's views:
Per argues that fluoride-salt reactor technology (AHTR/LFTR) has a clear path to achieve substantially lower energy production costs than ALWRs. His expectation is that this evolutionary path will remain focused mainly on thermal-spectrum reactors, with efforts to push to higher temperatures and efficiency, and the introduction of thorium. Sodium-cooled, metal-fueled reactors are intrinsically bulkier and lower temperature/efficiency than AHTRs and LFTRs, but are not intrinsically more expensive than ALWRs. IFR is more mature than AHTR and LFTR, so the big question is what will be the most practical route to commercial demonstration. IFR will be a tough sell, though, if the general perception remains that it is more expensive than ALWRs.
Barry intends to say more about this. In addition I should not that one factor that was missed, and that is the relative size of LFTR start up charges, which may be in a thermal LFTR only 1/10 that of a fast reactor. Cheaper and with more rapid deployment has been the Nuclear Green Rallying cry since December 2007. per is calling his reactor the Pebble Bed - Advanced High Temperature Reactor. It is at the very least a design exercise with an architecture that has a lot in common with graphite moderated MSRs. The major difference is that the fuel is in the graphite not the coolant salts. A hybrid is a compromise which borrows some features from each design, but throws out others. The PB-AHTR, makes some of its biggest cm promises in the area of nuclear safety. One of the PBRs safety features is based on its rather large core, a feature that the PB-AHTR eliminates. The MSR features a small core with the ability to limit reactivity be expelling part of the active core fuel content as core fluids expand with heat. Since fuel is dissolved in the core fluid, as the core fluid heats up it expands and starts flowing out of the core. With the decrease in fuel, core reactivity declines. Hence we loose significant safety features on both sides.

As Barry points out the AHTR is a converter not a breeder. Hence the AHTR does not offer LFTR level fuel burn-up. The AHTR does represent an amalgamation of two semi-mature technologies, and can probably move faster than say a MSBR could on its own. But there are costs for such expediencies. The LFTR is more where we want to go than the PB-AHTR. The LFTR will give us more flexible energy choices.


LarryD said...

An editorial in the UK Telegraph argues
for the US to go for Thorium Energy. It alludes to LFTRs in passing, though its mostly focused on Dr Rubbia's design.

Anonymous said...

To verify this I took some time to look this up from Dr. Peterson’s posts. When running in a pure thorium mode, the PB-AHTR will have a breeding ratio of between 1 and 1.07.


Charles Barton said...

Axil your statement is certainly plausible. Barry relies far to much on the sometimes off the wall claims of a few retired Argonne physicists and engineers.


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