Comparison of realistic large break LOCA analyses of a 3-loop Westinghouse plant using response surface and statistical sampling techniques

2 methods, used to make a realistic calculation of Loss of coolant accident (LOCA) are compared. Uncertainties in input data or in the analysis method must be considered. The first method is the best estimate loss of coolant accident methodology based on the 1996 evaluation model and the second is the realistic LOCA methodology using the automated statistical treatment of uncertainty method. Both methods used the same computer codes for thermal-hydraulics calculations of the primary system response and for fuel performance computation involving the local uncertainties. The first technique relies on response surface generation and applying Monte-Carlo technique to the regression model to characterize the PCT (peak cladding temperature) distribution and quantify the uncertainty. In this method, uncertainty contributors are ranged individually to compute PCT response. Later, these results are combined to generate a response surface. The other technique uses non-parametric order statistics where uncertainty parameters are sampled simultaneously for each transient calculation. The required number of transient runs depends on the desired tolerance intervals and is independent of the number of contributing uncertainty parameters. In this study a 3-loop Westinghouse plant is analyzed using each technique. The difference between the PCTs calculated using the response surface technique and the statistical sampling technique is 126 K. Most of this difference is attributable to the elimination of superposition assumption. The characteristics of the transient from both methods are very comparable. Same phenomena are predicted similarly in either methods