Verification and improvement of the SIROD code for fuel reliability evaluation

The SIROD code, developed at the Halden Reactor Project in Norway for the LWR fuel reliability evaluation, has been transferred to CRIEPI. The present paper describes the fuel performance models included in SIROD, the results of code verification and the improvement of the code to evaluate fuel reliability. The major features of the code are as follows. According to the verification by test and power reactor data, SIROD gives the reasonable value for the fuel performance such as fuel center-line temperature and fission gas release etc. However, cladding deformation by PCMI was shown to have the tendency of understimation. A number of the fuel performance models included in the code are based on the empirical equations obtained from the test reactor (HBWR) data. This makes SIROD a fast running code. The code, therefore, is the effective tool to process large amount of data, e.g. core-wide fuel failure analysis. The probabilistic approach is considered to be more relevant than the deterministic one for practical evaluation of fuel reliability. For this purpose, the model was assembled with the original SIROD, taking account of the uncertainties of the nominal power value and of the deterministic failure threshold calculated by SIROD. (author)