Vacuum Removal of Inert Radioactive Gases to Control the Tightness of Fuel Element Cladding of Fuel Assemblies of VVER Nuclear Reactors During Power Operation

A comprehensive approach is being developed to monitor the leak tightness of fuel rod claddings in VVER nuclear reactors. One of the main stages is the reliable registration of the presence of a leaking fuel rod or rods in the core of the reactor during the operation of the power unit at full capacity. This paper discusses general trends in the changes in the activities of radionuclides resulting from fission in the coolant of the primary circuit of VVER nuclear reactors of various generations and designs. The experience of the Novovoronezh Nuclear Power Plant in the method of sampling and isolating inert radioactive gases from the primary circuit coolant is examined. A comparison of methods for measuring inert radioactive gases in the primary circuit coolant is conducted, including direct spectrometry, cryogenic methods, and vacuum extraction methods. The issue of reliably recording the time of fuel rod cladding breach during the operation of the reactor installation at full power is addressed, using the example of power unit no. 5 of the Novovoronezh Nuclear Power Plant. Comparative results of the analysis of the state of the reactor core regarding the leak tightness of fuel rods are presented, based on key reference radionuclides. The most reliable results that indicate a fuel rod breach were obtained from monitoring specific activities and analyzing the changes in the ratios of inert radioactive gases, performed using the vacuum extraction method for inert radioactive gases. Monitoring the specific activity of inert radioactive gases in the primary circuit coolant allows a highly accurate assessment of the condition of physical barriers. The proposed method for extraction and isolation of inert radioactive gases demonstrates high reliability and consistency of results, as an additional tool for monitoring the leak tightness of fuel rod claddings during the operation of a power unit at full capacity. With representative data on the specific activities of inert radioactive gases, one can reliably assess the condition of the fuel rods in the reactor core.