PuO₂ and Fuel Residues

The isotopic composition of plutonium in storage and related special nuclear materials, advanced fuels and exotics changes with time as a result of radioactive decay; one principal example is the in-growth of americium-241 and the presence of curium-244.  The latter, given its significant predisposition to spontaneous fission, complicates the ease with which the isotopic composition is assessed via existing methods based on neutron multiplicity.  Often, it is necessary to carry out laboratory-based assessments, whilst long-established radiometric methods are currently dependent on ³He gas which is now no longer available.  In this project we will research to the use of fast-neutron multiplicity analysis (a technique via which the number of coincident neutrons arising from the fission decay of ²⁴⁰Pu_eff) is used to infer isotopic composition, in-situ.  This approach, if successful, will be real-time and more accurate than current ³He-based methods.  Specific focus will be made of the ability of the technique to discriminate between ²⁴⁰Pu_eff, ²⁵²Cf, ²⁴¹Am and ²⁴⁴Cm, with a diverse range of potential applications including plutonium accountancy in storage, criticality assurance and proliferation prevention in plutonium management scenarios.