METHODOLOGY TO ASSESS MINIMUM ACCIDENT OF CONCERN AND CRITICALITY ACCIDENT ALARM SYSTEM LOCATION

摘要

For nuclear facilities where criticality accident alarm systems are present or required, the minimum accident of concern and the criticality accident alarm system detector location must be determined to comply with regulatory requirements. This paper presents the methodology developed to establish the minimum accident of concern (MAC) and to determine the location, number and design characteristics of the criticality accident alarm system detectors. The methodology established at Chalk River Laboratories was demonstrated using a generic facility, referred to as "Building A", whose operations involve the use of ~(235)U as the fissile material of interest. The MAC defined for "Building A" included a description of the postulated critical system and the fission rate resulting in a total dose to free air of 0.20 Gy in the first minute, at 2 m away from the critical assembly . This information was subsequently used to determine criticality accident alarm system parameters. Demonstrating that criticality accident alarm systems, which have been historically installed in nuclear facilities, are able to detect the postulated minimum accident of concern is an important step in complying with current regulatory requirements. The methodology summarized in this paper has been successfully implemented for a number of nuclear facilities at Chalk River Laboratory and has been used to establish design requirements for acquisition and installation of new criticality alarm systems.