Development of a New Generation Computer Code (PRO-LOCA) for the Prediction of Break Probabilities for Commercial Nuclear Power Plants Loss-of-Coolant Accidents

In order to aid the Nuclear Regulatory Commission (NRC) in the process of making a risk-informed revision of the design-basis break size requirements for operating commercial nuclear power plants, a new probabilistic computer code (PRO-LOCA) is being developed, This code will aide the NRC in predicting leakage and rupture probabilities for critical piping systems as a function of break sizes. The PRO-LOCA code incorporates many enhancements in technology developed since some of the earlier probabilistic codes (e.g., PRAISE) were developed. These enhancements include improved crack stability analyses, improved leak rate models, improved weld residual stress solutions, improved crack initiation models, and new material property data. In addition, new degradation mechanisms, not previously considered in codes such as PRAISE were added. This included the addition of primary water stress corrosion cracking (PWSCC) for dissimilar welds in pressurized water reactors (PWRs). This paper reviews the development of the PRO-LOCA code by giving a brief description of its capabilities and the models embedded in the code. The current version of the PRO-LOCA code was used for a series of sensitivity analyses in order to test the robustness of the code for a full range of input parameters and to identify which input parameters have the greatest effect on the predicted leakage probabilities. The results from these sensitivity analyses are presented, as well as comparisons with other PFM codes (PRAISE). Details of which parameters appear to affect the leakage probabilities and the plans for future improvements to the code conclude this paper.