Development and assessment of U.S. Nuclear Regulatory Commission thermal-hydraulic system computer codes

A review is provided of the reasons why the US Nuclear Regulatory Commission needs thermal-hydraulic system computer codes, the assumptions and approximations contained within these codes, and the reasons why test data are required to assess the accuracy of the codes. Specific examples of codes and test programs are given. The use of computer codes assessed against data from scaled test facilities to predict the full-scale plant response is discussed. A method to help focus resources and the need for quantifying code uncertainties are discussed. This paper concentrates on the loss-of-coolant accident (LOCA) because most of the analytical and experimental research has been concentrated in LOCAs