Evaluation of the Zion risks for NUREG-1150

Zion is one of the five plants that have undergone detailed reanalysis as part of the US Nuclear Regulatory Commission's severe-accident research program. While Sandia National Laboratories (SNL) are the primary analysts for four of the five plants, Brookhaven National Laboratory (BNL) has performed the integrated analysis of Zion. This paper discusses major areas of improvement to the preliminary version of the Zion study. The final version of the Zion analysis now enjoys an equal level of modeling detail and of plant specificity as that of the remaining reference plant studies. The primary improvements to the draft analysis are (a) greater extent and detail of the systems analysis, (b) the generation of a plant-specific phenomenological data base by implementation of mechanistic severe-accident codes, (c) the formal elicitation of expert judgment on Zion-specific issues, and (d) improvement of the methodological framework for the probabilistic propagation of uncertainties