Study Of Instrument Survivability Evaluation Methods During Severe Accident In Nuclear Power Plant

The purpose of the instrument survivability assessment is to evaluate theavailability of the instruments during severe accident. By analyzing and proving theinstruments that are used for relieving and monitoring the progress of severe accidentcould keep available in required time, the result could help to set down the SevereAccident Management Guidance (SAMG). However, it’s still unsolved that how toanalyze the instrument survivability in standard, while standards like HAF102clearlyrequire that instruments should be available during severe accident. Therefore, it’snecessary to make further study on severe accident environment phenomenon, as wellas the method of evaluating the survivability of instrument.The main content of this paper consists of three parts. The first one is theestablishing of instrument survivability evaluation progress, the second one iscompleting and application of the enveloping method, the third one is analyzing andapplication of circuit simulation method.The first part of the article begins with the study of relevant regulations andstandards, as well as the environmental conditions in severe accident. These help toclear the requirements and direction of the evaluation. On the basis of the existingmethods, the evaluation progress is optimized and improved.The second part is the study and application of enveloping method. Method ofenveloping is to compare the curve of the instrument qualification the accidentenvironment. With additional research of sensitivity to environment of instruments,effects could be evaluated. This method gains high credibility, while it’s veryconservative. Especially when qualification curve could not envelope theenvironment curve, whether the instrument still survives or not is not easy to answer.Thus a new method as complementary is badly needed to make further assessment.The second part is the study and application of circuit simulation method.Method of circuit simulation is initiated by this paper. The main thought of this method is using computer program to calculate the output waveform circuit underparticular circumstance. For this, a simplified equivalent circuit and typical degradedcharacteristics need to be well considered. According to the waveform, survivabilitycould be judged by some criterions.At the end of the part,the rationality and reliabilityof the method are analyzedby the comparison tothe instrument survivabilityinspection reports of Three Mile Island.This research has provided a practical method for instrument survivabilityassessment. It’s got great value for engineering application.