DETERMINATION OF CODE ACCURACY IN PREDICTING SMALL-BREAK LOCA EXPERIMENT

Quantitative evaluation of thermal-hydraulic code uncertainties is a n ecessary step in the code assessment process, especially if best-estim ate codes are utilized for licensing purposes. With the goal of quanti fying code accuracy, researchers in the past developed a methodology b ased on the fast Fourier transform (FFT) that consisted of qualitative and quantitative code assessment. Here, the FFT-based method is appli ed to International Atomic Energy Agency (IAEA)-Standard Problem Exerc ise (SPE)-4 test results with pre-and posttest code calculations of th e IAEA-SPE-4 experiment. Four system codes (ATHLET, CATHARE, MELCOR, a nd RELAP5) are used for calculations of the experiment, performed at t he PMK-2 facility, which simulated a cold-leg break in a VVER-440 plan t. The results show that the posttest calculations had better accuracy than did the pretest calculations. None of the best three pre-and pos ttest calculations were able to predict core dryout, which was the mos t important phenomenon observed during the test. The results obtained can give an objective indication of the capability of the aforemention ed codes in predicting relevant variables characterizing the transient (too few experimental parameters may limit full application of the FF T-based methodology).