Statistical analysis of dewpoint data record at OWL-1 loop cubicle and its application to early detection of abnormal water leakage from the loop

A method of statistical analysis was applied to analyze the dewpoint data record of both supply and exhaust air for OWL-1 (Oarai Water Loop No.1) loop cubicle in JMTR (Japan Materials Testing Reactor). The primary purpose of the present study is to determine experimentally the dynamic interrelationship between these two quantities and then to evaluate the effectiveness of incorporating the information thus derived on the dewpoint dynamics into a water leakage monitoring system for the OWL-1 loop. Through the data analysis, it was shown that; The dynamics of dewpoint between the supply and exhaust air contain basically two mode characteristics; i.e. the fast mode with a time constant of about ten minutes and the slow one with that of about several hours. Under normal condition without any water leakage from the loop, variations of the exhaust dewpoint for frequencies below about 2 cycle/hour are mostly due to those of the supply dewpoint. Based upon the results mentioned above, a simple filter including the dewpoint dynamics was designed in an attempt to develop an efficient leak monitor for the OWL-1 loop system. This filter was applied to analyze the dewpoint data record during the time when the OWL-1 loop underwent an abnormal water leakage in the 43rd cycle of JMTR operation. The results of the analysis indicate potential usefulness of the present method for detection of abnormal water leakage at its early stage. The basic idea for the leak monitor proposed here is considered to be applicable also to the problem of water leakage detection at power reactor plants in general. (author)