Structured sensitivity analyses using the MAAP 2.0 computer code

An analytical study was performed to determine the sensitivity of radiological source terms using the MAAP 2.0 computer program for two reference plants, i.e., Peach Bottom (BWR Mark I) and Sequoyah (ice condenser PWR). The fission products released to the environment were calculated for two risk dominant accident sequences at the two plants. The calculations showed that fission product retention in reactor coolant and containment systems would be greater than previously estimated and the source terms would be lower. The sensitivity evaluation performed considered cases which fall into three separate categories: (1) rebaselining of IDCOR-comparable base cases and determination of time-step and spatial nodalization sensitivities; (2) sequence description sensitivity variations primarily caused by differences in system behavior and operator actions; and (3) sensitivity variations in phenomenological parameters. The results of the sensitivity studies are presented graphically in summary tables, showing the variations made and the resulting value of various ''figure of merit'', including key event times (e.g., time to containment failure) and fission product deposition and release information. This report describes the details of the calculations, including the methodology employed, plant input data used and conclusions drawn from the results obtained