Development of a subchannel model within the answers software service WIMS reactor physics code

A subchannel model is currently being developed as a new integrated capability within the Answers Software Service WIMS reactor physics code. This forms part of a goal to develop WIMS into a whole core reactor analysis model. Recently WIMS has been extended to include 3-dimensional whole core flux solvers based on the Method of Characteristics (CACTUSOT) and the SP3 approximation (latter includes precursors and time dependence). The SP3 solver is currently used to calculate a power source for the new subchannel model. The subchannel model updates the materials on the WIMS interface (the data storage area used to link WIMS modules) with new temperatures and densities following the thermal hydraulic calculation. This initial coupling approach between neutronics and thermal hydraulics permits dynamic cross section re-shielding via equivalence or sub group theory. This paper describes the current capability of the new subchannel model integrated within WIMS. Verification is presented via comparisons to COBRA-En. Validation is presented for the OECD/NRC NUPEC PSBT single channel experiments [1] where agreement is observed to be comparable to other codes. An example of a coupled (SP3, subchannel, dynamic cross section shielding using equivalence theory) transient induced via varying the inlet mass flow rate for a typical PWR pin and channel is then presented. (Author)