Discussion on DEC of High-level Radioactive Waste Liquid Storage System from the Perspective of Multiple-failure

The analysis of design extension condition (DEC) is an important part of the analysis of beyond-design-basis accidents of nuclear power facilities. Currently there is no such practice in the field of post-processing facilities. The high-level radioactive waste liquid storage system of the post-processing facility is taken as the research and demonstration object. Based on engineering judgment and deterministic methods, DEC is identified from the perspective of multiple-failure. The results show that among the 29 working conditions of high-level radioactive waste liquid storage system, 14 conditions will not cause excessive release of radioactive substances to the environment, which belongs to DEC; 8 conditions may cause excessive release of radioactive material to the external environment. If the concrete pouring layer has the function of containing the waste liquid and the equipment room has the function of venting or anti-explosion, then these 8 conditions will not cause excessive release to the external environment and can also be included in DEC. The remaining 7 conditions will cause excessive release of radioactive material to the external environment. By improving the equipment reliability of exhaust filtration and chimney in the filter room of orange area, the magnitude of radioactive aerosol release to the environment shall not exceed the release level of hypothetical accident of siting.