Progress with algorithm and vector/parallel enhancements for Relap5/Mod2 thermohydraulic system simulation code

Earlier experience resulting from attempts to develop a parallel implementation, and a vector implementation for RELAP5/MOD1, using super computers, resulted in an analysis suggesting a five to ten times performance enhancement for future versions of the code. The MOD2 version of the code, presently available, uses a six equation model (vs. five equations in MOD1) with the option of a semi-implicit or nearly-implicit numerical solution scheme. The nearly-implicit numerical scheme violates the convective (material) Courant limit. The RELAP5/MOD2 code has been implemented on CDC Cyber 176, CRAY 1S and CRAY X-MP/48 computers. Algorithm performance enhancements and vector performance improvements have been measured and are analyzed for these three computing machines. The reactor small break loss-of-coolant problem, used in previous studies, was employed as the basis for the present analysis. Previous studies performed to compare the performance of algorithms in MOD2 are compared to MOD1, using the two presently available numerical methods in MOD2. Planned vector and parallel enhancements are discussed in the context of past studies, and expected future performance gains. Applicability of the RELAP5 code to best estimate real time simulations and nuclear power plant simulators is discussed