Dose rates modeling of pressurized water reactor primary loop components with SCALE6.0

Abstract

The SCALE6.0 simulation model of a typical PWR primary loop components for effective dose rates calculation based on hybrid deterministic–stochastic methodology was created. The criticality sequence CSAS6/KENO-VI of the SCALE6.0 code package, which includes KENO-VI Monte Carlo code, was used for criticality calculations, while neutron and gamma dose rates distributions were determined by MAVRIC/Monaco shielding sequence. A detailed model of a combinatorial geometry, materials and characteristics of a generic two loop PWR facility is based on best available input data. The sources of ionizing radiation in PWR primary loop components included neutrons and photons originating from critical core and photons from activated coolant in two primary loops. Detailed calculations of the reactor pressure vessel and the upper reactor head have been performed. The efficiency of particle transport for obtaining global Monte Carlo dose rates was further examined and quantified with a flexible adjoint source positioning in phase-space. It was demonstrated that generation of an accurate importance map (VR parameters) is a paramount step which enabled obtaining Monaco dose rates with fairly uniform uncertainties. Computer memory consumption by the SN part of hybrid methodology represents main obstacle when using meshes with large number of cells together with high SN/PN parameters. Detailed voxelization (homogenization) process in Denovo together with high SN/PN parameters is essential for precise VR parameters generation which will result in optimized MC distributions. Shielding calculations were also performed for the reduced PWR facility model which included only reactor core and adjacent concrete structures with the steam generator and the pump. Hybrid FW-CADIS methodology appears to be very effective for shielding calculations of complicated MC geometries. It was demonstrated that definition of air as a global adjoint source gave lower uncertainty of photon dose rates. Activation of the primary loop coolant, which becomes additional gamma source in operating reactor, was considered. Compared with analog MC simulations, the hybrid methodology drastically improved Monaco distributions in quality as well in space coverage.The SCALE6.0 hybrid stochastic methodology was thoroughly investigated and its versatile ability for deep penetration models was proved. A careful selection of parameters can relax high CPU time and hardware requirements.