Part 21 Report - 1998-690

A defect was discovered in an input option for the BWR Fast Transient Analysis Code BISON-SLAVE. The defect could lead to the establishment of non-conservative Minimum Critical Power Ratio (MCPR) Operating Limits in certain Boiling Water Reactor plant technical specifications. The input option error in the BISON-SLAVE code is not applicable to analysis performed for Pressurized Water Reactors.

The defect identified involves an input option that was incorrectly described in the code's user manual and not in the program coding itself. The incorrect description leads an analyst to use an incorrect option when modeling the radial power distribution which leads to the calculation of non-conservative MCPR Operating Limits in some situations. An evaluation of the defect by ABB-CE has shown that there is currently no safety problem for either of the involved reactors, Washington Public Power Supply System Project Unit-2 or Pennsylvania Power and Light Susquehanna Unit-1.