High performance light water reactor core design studies

The High Performance Light Water Reactor (HPLWR) is the European version of the various supercritical water cooled reactor proposals. The paper presents the activity of KFKI-AEKI in the field of neutronic core design within the framework of the European funded project: 'HPLWR Phase 2'. As the coolant density along the axial direction shows remarkable change, coupled neutronic-thermohydraulic calculations are essential which take into account the heating of moderator in the special water rods of the assemblies. A parametrized diffusion cross section library was prepared for the HPLWR assembly with the MULTICELL neutronic transport code. The parametrized cross sections are used by the KARATE program system, which was verified by comparative Monte Carlo calculations. Methodical core calculations have been carried out. Without thermal insulation in the second superheater of the three pass core, the temperature of moderator water exceeds the pseudocritical temperature resulting in poor moderation. Applying heat insulators helps to avoid the extreme heat up of moderator, so it provides better moderation for neutrons. The increase of the local multiplication in the superheaters favorably affects the power distribution and keff of the core. Preliminary loadings of the HPLWR core were assessed, which contain insulated assemblies with Gd burnable absorbers. The initial reactivity excess was compensated by control rods. The reactivity coefficients of HPLWR with respect to temperatures show substantial negative feedback at normal operating conditions. (author)