CANDU 9 Large LOCA Uncertainty Analysis

Abstract

This paper describes the application of a structured approach for the uncertainty assessment to a postulated limiting large Loss-of-Coolant Accident (LOCA) for the CANDU 9 reactor. The structured approach is based on an integrated three step process of code, representation, and plant uncertainty assessment. The process is made manageable by ranking important phenomena/parameters and assessing only the most important uncertainty sources. The analysis is structured into power pulse phase followed by blowdown phase. A fractional factorial Latin hypercube experimental design is used to determine the calculation matrix for each phase. The power pulses obtained in the power pulse phase are used as one out of a total of five key input (uncertainty source) parameeters in the blowdown phase. Based on the results of the calculation matrix of the blowdown phase, a response surface for the maximum sheath temperature as a function of the five input uncertainty source paramters is generated. The response surface is randomly sampled to generate the probability distribution function and the associated 95% confidence level for the maximum sheath termperature. Finally, this maximum sheath temperature is adjusted with additional identified biases. The results show that the acceptance criteria of no sheath melting is met with high confidence level.