An alternative to the SAS2H/ORIGEN-S sequence to account for water-density effects in BWR systems

A scheme to generate one-group problem-dependent cross-section libraries for point-depletion calculations with the ORIGEN-S code was developed as an alternative to the SAS2H sequence of the SCALE code system. The methodology, named Automatic Rapid Processing (ARP), generates libraries by interpolating in SAS2H precomputed cross section libraries. The method has been used to generate ORIGEN-S cross section libraries on a personal computer resulting in a great reduction of computer time without a sacrifice of accuracy over that required by corresponding SAS2H calculations. The ARP scheme generates ORIGEN-S libraries by interpolating in burnup and enrichment for PWR assemblies. The intent of this work is to describe a procedure which extends the application of the ARP methodology to BWR assemblies by including the axial water-density effects in the generation of the ORIGEN-S cross-section libraries. The axial liquid- to-steam change of state in BWR systems leads to a variation in the water density and significant cross-section changes as a function of the water density. To account for the axial water-density changes in a SAS2H calculation, the water density is entered explicitly in the generation of the one-group ORIGEN-S cross-section libraries generated from the SCALE 27-group library. In its original version, ARP does not account for the effects of water-density variation in ORIGEN-S cross-section library generation, and, therefore, its application is restricted to systems for which the impact of this parameter is negligible. To update the ARP methodology to account for the water-density effect, a detailed study of the cross-section change with this parameter was performed with an 8 x 8 (General Electric) BWR assembly.