Research on Experiment Evaluation Method for Thermal Ratchet of Nuclear Equipment at CPR1000 Nuclear Power Station

For the question that RCC-M criteria can not make a security assessment for the ratchet phenomenon of some components, the experience analysis method of thermal ratchet was introduced, and a more detailed thermal ratchet analysis of the electrically heated pressurizer spray nozzle at the CPR1000 nuclear power plant was presented by the Efficiency Design Curve method and the Ratio Curve method. The results achieved indicate that the RCC-M thermal ratchet evaluation criteria are too conservative and the more accurate experience analysis method can improve the economics of nuclear power construction.