Improvements to MONK and MCBEND enabling coupling and the use of MONK calculated isotopic compositions in shielding and criticality - 7-20

Isotopic composition through time can be derived for 3D reactor core configurations using the Monte Carlo Criticality and Reactor Physics code MONK. MONK can be coupled to thermal-hydraulics (TH) codes (e.g. RELAP5) to model temperature feedback and coupled to the Monte Carlo radiation transport code MCBEND for onward neutron and/or gamma calculations. MONK derived isotopic compositions can be directly and automatically transferred to another MONK or MCBEND model for either subsequent: -) burn-up steps or branching calculations with MONK using the same 3D whole core model; or -) shielding calculations with the compositions transferred to MCBEND utilised as elemental compositions of reactor components or fuels (for example in the case of a fuel flask or waste storage facility); or -) criticality calculations with the compositions transferred to another MONK model. Results from a typical whole core PWR calculation with MONK are presented demonstrating MONK TH code coupling and generating burnt-up isotopic compositions. The compositions from three PWR fuel assemblies were automatically transferred to separate MCBEND and MONK models of a fictitious spent nuclear fuel facility performing shielding and criticality calculations respectively. Results are presented to demonstrate the reactivity differences and how burn-up credit may be used. An innovative scheme for speeding up MONK and improving resolution of MONK burn-up/TH meshes utilising parallel computing architecture is described. This will enable refinement of isotopic composition variations even further. The parallelization scheme utilises a novel domain decomposition method, enables optimisation for user controlled calculation speed adjustment and has the potential for adaptive meshing. (authors)