A Feasibility Study to Estimate the Subcriticality at a PWR Startup

摘要

For the safe and efficient operation at a subcritical reactor core, the subcriticality of the core is very important information. So far in the commercial nuclear industry, this information can only be inferred, not directly measured. Recently, Westinghouse has developed the Spatially Corrected Inverse Count Rate (SCICR) method for subcritical reactivity measurement via the use of ex-core detector signal measurements and advanced subcritical core condition predictions. In JAPAN, the digital reactivity meter coupled with the modified neutron multiplication method (NSM) was developed and applied to several PWRs But both SCICR and NSM has to measure the reference core reactivity through other conventional techniques at the nearest critical condition. If one can measure the subcriticality of a commercial PWR core, he/she can speed up the process of approaching criticality as well as reduce the critical path time to power ascension. But at present, although there are many methods to measure the subcriticality of various research or criticality reactors, there is no concrete and well-defined way to measure the subcriticality of a PWR core. Recently, in order to measure subcriticality for a PWR, KEPRI investigated the applicability of Feynman-a technique (or variance-to-mean method) using measured source-range excore detector signals. This paper is going to discuss the some experimental results.