Selection of Complex Accident Sequences for Sodium-Cooled Fast Reactor Design Extension Conditions

Abstract

Design Extension Conditions (DEC) are accident conditions beyond design basis for nuclear power plants, including complex accident sequences (DEC-A) and severe accidents (DEC-B). As required by the nuclear safety regulation HAF102-2016, DEC must be considered by identifying additional accident scenarios and develop practical prevention and mitigation measures for such accidents in design process for nuclear power plants. The aim is to enhance nuclear power plant’s response to beyond design basis accidents or multi-fault accident. It’s to contribute to increase the design requirements and expand the design consideration for nuclear power plants to consider DEC in design process, which may increase the design difficulty and construction and operation costs for nuclear power plants. The selection of DEC is great significance to balance the safety and economy for nuclear power plants. Compared with DEC-B, the DEC-A is a newer concept, and the mature cognition of DEC-A has not yet been reached. The selection method of DEC-A for sodium-cooled fast reactor is analyzed systematically, which includes how to define, identify and screen DEC-A. Taking a sodium-cooled fast reactor as an example, DEC-A are identified and screened in the method of the combination of probabilistic safety assessment, determinism and engineering experience, and the entire selection process of DEC-A is performed. Besides, It is analyzed and discussed about the application of DEC-A in safety analysis and safety design of sodium-cooled fast reactors. Existing study results will provide theoretical reference for determining DEC-A lists for similar reactors.