ADSRs: Proliferation issues

1
ADSRs Proliferation issues

• Roger Barlow
• ADSR08
• Manchester, 9th September 2008

2
Issues and Questions

• Dirty bomb
• Little boy type device
• Fat man type device
• Role of 232U

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.
• Wikipedia

4
Enriched Thorium

• No

5
233U device

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

6
232U

• 232U decays with a half life of 69 y, producing
  228Th 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 200-1000 rem
• 2.4 contamination is needed to make 233U
  safe

7
Origins of 232U

• 233U(n,2n)? 232U
• 4 mb for neutron energies above threshold 6 MeV
• 232Th(n,2n)? 231Th ? 231Pa 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

8
Possible loophole

• Chemically isolate the 233Pa.
• Wait (27 d half life) for it to decay to pure
  233U
• Some MSR schemes use just this

9
Ionium to the rescue

• Ionium is 230Th
• It does not occur in Thorium, which is pure 232
• It does occur in Uranium, part of the 238U decay
  chain
• spike the Thorium with Ionium

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

11
Conclusions

• Safety depends on design
• Advantage to have all fuel exposed to fast
  neutrons to ensure 232U concentration
• Ionium may be needed