Impact of surveillance test interval extension on the core-melt frequency: a methodological approach

The objective of this paper is to compare the traditional method used to determine the risk impact associated with the extension of a surveillance test interval (STI) with a computerized one, such as Living PSA (LPSA) or a Risk Monitor System (RMS), over the base-line risk of the facility. PSA techniques and methods (also called traditional methods) have been used in order to show all necessary steps hat should be performed during the risk calculations associated with an STI extension, considering the contributions due to accident sequences which demand the safety injection system, common cause failures and human errors. The discussion is centered on the importance of having a on-line computerized system, LPSA or RMS, that can calculate, in a simple fashion, changes in the base-line risk due to a continuous change in plant configurations and their operating procedures as compared to the procedure for calculating the risk level increase due to STI extension without a LPSA or RMS. (author). 10 refs