Comprehensive signal validation for nuclear power plants

The optimal control and safe operation of a nuclear power plant requires reliable information concerning the state of the process. Signal validation is the detection, isolation and characterization of faulty signals. Properly validated process signals are beneficial from the standpoint of increased plant availability and reliability of operator actions.

A signal validation technique utilizing a process hypercube comparison (PRC) was originated during the research and other methods were extended. The hypercube is merely a multi-dimensional joint histogram of the process conditions. The hypercube is created off-line during a learning phase. In the event that a newly observed plant state does not match with those in the learned hypercube, the PRC algorithm performs signal validation by progressively hypothesizing that one or more signals is in error. This assumption is then either substantiated or denied. In the case where many signals are found to be in error, a conclusion that the process conditions are abnormal is reached.

A comprehensive signal validation software system has been developed for application to nuclear power plants. This system combines some previously established fault detection methodologies as well as some newly developed ones. The techniques have been implemented in a modular iii architecture which allows the addition or removal of signal validation "modules" as deemed necessary. Intra-module confidence factors describing the validity of a given signal are derived using fuzzy membership functions. A final evaluation of signal status is made by the System Executive (SE) based on results from each signal validation module. In order to make reliable decisions in this parallel system a positive decision maker (PDM) was developed.

Both the hypercube signal validation methodology and the comprehensive system were tested using operational data from a commercial pressurized water reactor (PWR) and the Experimental Breeder Reactor II (EBR-II).