Development of RAPID transport calculation with heterogeneous temperature distribution

The RAPID hybrid transport code, based on the fission matrix method, has been developed and previously proven successful on BEAVRS benchmark at hot-zero-power condition. In this work, it is extended to the BEAVRS model to include fuel and moderator temperature feedback. The bi-linear fission matrix interpolation technique was applied to several artificial fuel and moderator temperature distributions. For almost all cases, it provides an accurate calculation result with a k_eff difference smaller than 70 pcm and 2D pin-wise RMS error smaller than 1% compared to Serpent 2 Monte Carlo reference. In order to decrease the number of databases needed, a plane interpolation routine is developed, which de-couples the fuel and moderator temperature. The RAPID calculation with the plane interpolation reports a similar accuracy to that with the bi-linear interpolation. The bi-linear interpolation required 24 database points from Monte Carlo calculations, while the plane interpolation only needed 10. The plane interpolation allows RAPID to prepare fewer databases while preserving a high accuracy.