Application of KARATE to Supercritical Water Reactors
16th Symposium of AER on VVER Reactor Physics and Reactor Safety (2006, Bratislava, Slovakia)
Actinide Transmutation and Spent Fuel Disposal
Abstract
The overall objective of the HPLWR project was to assess the feasibility of a High Efficiency Light Water Reactor operating at thermodynamically supercritical region. In a once-through concept, the water enters the reactor as water and exits as high pressure steam without change of phase. An efficiency of over 40% is expected. The evaluation and improvement of the Japanese concept was carried out by eight institutions within the 5th Framework Programme of the EC. Our role was to perform neutronic transport and core diffusion calculations. 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 hexagonal assemblies. We have prepared a parametrized diffusion cross section library of the HPLWR assembly at low burnup. The parameter range covers the cold zero power and hot full power states. The feedback parameters are calculated with the SPROD code of the Tokyo University, which was coupled with the KARATE core calculation module. Preliminary core calculations have been done to demonstrate the applicability of the code. During the HPLWR core calculations the two energy group structure was used in the coupled KARATE-SPROD code system. Because of the coolant axial density change the need for checking the applicability of the two-group structure emerged. Cross section calculations were performed with the MULTICELL deterministic transport code for the reference fuel assembly without Gd absorbers at zero burnup. The technological parameter range (coolant density, water rod density, 135Xe concentration, fuel temperature) corresponded to the nominal conditions. The multigroup cross sections were collapsed to 2, 4 and 6 group diffusion type cross sections using the criticality spectrum (B1 equations) for each parameter combination. The cross sections were used to calculate one representative assembly. The temperature and equilibrium Xe distributions were calculated with the KARATE-SPROD nodal code using 2 energy groups. The SNAP finite difference (FD) code was used to study the effect of the 2, 4 and 6 group scheme, where the cross sections were based on the frozen distributions. The results showed that the maximum deviation between the multiplication factors was about 0.2 %, so the use of the limited number of groups in this calculational scheme does not lead to considerable error.