Using the LEPRICON System To Evaluate Best-Estimate Vessel Fluence at Ulchin NPP Unit 1

The accurate estimation of fast (E {>=} 1 MeV) neutron vessel fluence is very important because it is a crucial factor for the reference nil-ductility temperature (NDT) shift ({Delta}RT{sub NDT}). Recently, there has been a growing interest in best-estimate vessel fluence in Korea as elsewhere due to the proposed life-extension programs of the nuclear power plants. In this paper we report the results of best-estimate evaluation of the vessel fluence at Ulchin nuclear unit 1 (Ulchin-1) in Korea. Ulchin-1 is a pressurized water reactor of the Framatome type rated at 2775 MW(thermal) and in operation since 1988. We used the LEPRICON code system. First, to validate LEPRICON, we have revisited a previous analysis of the VENUS-1 experiments using the ELXSIR library based on ENDF/B-V Mod 3, which has updated iron cross sections. Then, three surveillance tests performed at the plant were used in the LEPRICON analysis.