ADSRs: Proliferation issues Roger Barlow ADSR08 Manchester, 9 th September 2008

Roger BarlowUK ADSR ProgrammeSlide 2 Issues and Questions ‘Dirty bomb’ ‘Little boy’ type device ‘Fat man’ type device Role of 232 U

Roger BarlowUK ADSR ProgrammeSlide 3 “Dirty Bomb” (Spent) fuel rods will contain fission products Dispersal over civilian areas would cause panic, expense, and few fatalities It is thought that during the 1960s the UK Ministry of Defence evaluated RDDs, deciding that a far better effect was achievable by simply using more high explosive in place of the radioactive material.UK Ministry of Defence Wikipedia

Roger BarlowUK ADSR ProgrammeSlide 4 Enriched Thorium No

Roger BarlowUK ADSR ProgrammeSlide U device In principle possible Critical mass ~15kg No spontaneous fission problems: simple gun-type device 233 U in fuel stabilises after about 5 years. Extract chemically from Thorium Is this possible? Presumably. If not, easy to find out

Roger BarlowUK ADSR ProgrammeSlide U 232 U decays with a half life of 69 y, producing 228 Th which decays producing a 2.8 MeV  ray. Really nasty stuff 5 ppm 232 in 233 gives (long term) ~190 mrem/hr for a worker 0.5m from a 5kg sphere. Health and safety limit 5 rem/y. Lethal doses rem ~2.4% contamination is needed to make 233 U ‘safe’

Roger BarlowUK ADSR ProgrammeSlide 7 Origins of 232 U 233 U(n,2n)  232 U 4 mb for neutron energies above threshold ~6 MeV 232 Th(n,2n)  231 Th  231 Pa followed by (n,  ) 14 mb for neutron energies above threshold ~6 MeV Fast neutrons from tail of fission spectrum – or spallation Asymptotic ratio for the Energy Amplifier is 0.15%

Roger BarlowUK ADSR ProgrammeSlide 8 Possible loophole Chemically isolate the 233 Pa. Wait (27 d half life) for it to decay to pure 233 U Some MSR schemes use just this

Roger BarlowUK ADSR ProgrammeSlide 9 Ionium to the rescue Ionium is 230 Th It does not occur in Thorium, which is pure 232 It does occur in Uranium, part of the 238 U decay chain ‘spike’ the Thorium with Ionium

Roger BarlowUK ADSR ProgrammeSlide 10 Messy alternative Add 238 U to ‘denature’ the fuel. 12% 233 in 238 corresponds to 20% 235 in 238 and is deemed unenriched and safe

Roger BarlowUK ADSR ProgrammeSlide 11 Conclusions Safety depends on design Advantage to have all fuel exposed to fast neutrons to ensure 232 U concentration Ionium may be needed