by Doug Coulter » Fri Nov 13, 2015 4:35 pm
it's a thought. There ARE things that fast-fission, but nothing with a huge neutron absorption cross section, and of course fission makes yet more neutrons (2+ per) - with about the same energy as we had already. Our neutrons are right at the low end of the range for fast-fissioning U-238... Nothing magically stops those either. Down near thermal (but above it, at a few eV, used to be classified info), U-238 has a big cross section, to be bred into 239, eventually becoming plutonium after a beta decay into Np239 and a further decay of that into Pu. Which is why most fission reactors need a moderator and segmented fuel to slow the neutrons below that big peak before they encounter U-238 in the fuel, else they'd be lost and you couldn't get to critical mass without extreme enrichment (See Fermi and his first big project there). I hope we can think of something more useful to do with neutrons - other then just letting them make gamms by decay or capture for heating. Like make medical isotopes and such. But about the best way to stop them - and the resulting gammas, is a big water bath (which could be in supercritical conditions for water), which we kind of need for a boiler anyway.
After all, if you're making neutrons with 2.5 Mev on them, you have a lot of possibilities, and I'd point out that this makes everyone's calculations of energy wrong - because when one is absorbed or decays, there's another approximately 2 MeV released, added to the original reaction output. It improves the number by around 23% or so.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.