Determining Prompt Fractions of In-Core Flux Detectors During Full-Power Operation in CANDU

Abstract

This paper presents analysis of in-core flux detector (ICFD) response data acquired during reactor full-power operation in Darlington unit 1 and in Point Lepreau. The purpose of the analysis is to determine the high-frequency response or "prompt-fraction" of the reactor control and safety system ICFDs. Two types ofICFD response data are analyzed: (a) high-fidelity (16-bit), highspeed (100 Hz, 50 Hz) data acquired during near 100% full-power, steady-state reactor operation, and (b) 16-bit, 6 s sampling interval data acquired during a rapid power reduction of approximately 2% just prior to refueling (in Point Lepreau only). Under the assumption of a constant in-core flux-shape during near steady-state operation, it is shown that the high-frequency ICFD gain can be determined to a statistical accuracy of the order of a percent, comparable to the accuracy of effective prompt fractions determined from reactor trip tests. Systematic inaccuracies, due to the analysis assumptions, are explored. Other reactor-core and controlsystem characteristics that can be ascertained from high-fidelity, high-speed in-core flux detector response data are briefly discussed. The results demonstrate that high-fidelity, high-speed ICFD response data acquired during normal station operations can serve as an on-line health monitoring or surveillance tool for CANDU reactor-core instrumentation, control and safety systems. In particular, ICFD prompt fractions, an important parameter of control and safety system performance, can be determined to an accuracy comparable to the accuracy from reactor trip tests. These data provide timely information about performance and can aid in planning for maintenance work during outages. The paper makes recommendations for the routine acquisition and use of such data in operating CANDU stations.