LOCA Criteria Basis and Test Methodology

Acceptance criteria for emergency core cooling systems (ECCS) define the maximum temperature and degree of oxidation in order to avoid excessive embrittlement and hence failure of the fuel cladding, which would affect core cooling in the case of a loss-of-coolant accident (LOCA). The criteria are mainly based on experimental data obtained in the 1970s-80s. Several types of tests have been performed to evaluate structural integrity and embrittlement of the cladding under LOCA conditions, and consequently different test methodologies have been used for determining the cladding embrittlement criteria. The current trend towards high burn-up and the use of new cladding alloys has increased the need for international discussions on these test methodologies and acceptance criteria. In response, the NEA Committee on the Safety of Nuclear Installations (CSNI) and its Working Group on Fuel Safety produced this technical opinion paper, which should be of particular interest to nuclear safety regulators, nuclear power plant operators and fuel researchers.