Computing Radiation Fields in Light Water Reactor Internals Using Discrete Ordinates (S_N) Method

摘要

We have performed discrete ordinates calculations to determine detailed three-dimensional neutron and gamma flux distributions in BWR reactor internals. Because of the large physical size, we have partitioned the model into three axially overlapping regions of interest including: a. core lower plate, b. jet-pump assemblies, and c. core spray piping. We have performed 2-D (r-z) adjoint function calculations to determine the regional contributions of neutrons and gamma rays to dpa/s and acquired effective model volumes/sizes for each region for subsequent 3-D models. Then, we have performed fixed source, 3-D Cartesian, 67-group (47-group neutron, 20-group gamma), P_3, S_8 discrete ordinates calculations using the PENTRAN code and obtained neutron and gamma fields in the reactor internals. These detailed neutron and gamma maps can further be used by the nuclear utilities to relate to the actual material damage through displacement per atom and/or to calculate the transmutation fraction of Boron and Nickel into Helium as a function of fluence.