14.33. The reactor operator must be able to react quickly to indications of abnormal conditions. Expert systems can help provide the information needed for effective action. For example, an expert system for PWR op­erator support would consist of several subsystems, each having a different function. A diagnosis subsystem identifies an abnormality. Without as­sistance, an operator confronted with various offnormal meter readings would have to infer the basic cause. Similarly, multiple alarms triggered by limit exceeding conditions may not be helpful in pinpointing the malfunction.

14.34. In one type of diagnosis subsystem or module, logic trees are prepared from a knowledge or “rule base” relating symptoms, such as those indicated by meters or alarms, to basic faults. A pattern search then seeks one or more matches. As a simplified example, consider leakage in the reactor coolant system (RCS) as the fault. If we had a high charging — rate flow alarm and an indication that the pressurizer level was decreasing, the search would conclude that RCS leakage was likely, which then could be verified by additional signals.

14.35. Once a fault has been identified by the diagnosis module, the computation moves to an operational guidance module which calls upon an expert knowledge base to provide corrective measures. In our simplified example, a load reduction and perhaps reactor trip would be indicated. However, for a more sophisticated case, a less obvious action might be recommended.