Study on Interfacing System LOCA of VVER-1200

Abstract

The evaluation of public risk at nuclear power plants has generally found the risk to be very low. Part of the reason for the low assessed risk can be attributed to the “defense-in-depth” philosophy of nuclear power plants. This defense-in-depth includes multiple barriers to prevent the release of radionuclides to the environment. Nevertheless, accident scenarios have been postulated which might compromise the defense-in-depth by bypassing the reactor coolant system boundary and the containment. One such accident type is referred to as the interfacing system LOCA (ISLOCA). This type of sequence involves the loss of isolation between the high pressure RCS and a low pressure system outside containment. ISLOCA could lead to the loss of coolant outside containment while simultaneously disabling ECCS injection. Such a scenario could result in core damage and might have substantially higher consequences than some of other postulated severe accidents because the containment is also bypassed. Thus, it is necessary to calculate the ISLOCA risk for a specific nuclear power plant. Based on summarizing the ISLOCA analysis method and process, this article carried out the ISLOCA analysis for the VVER-1200 nuclear power plant, identified its typical ISLOCA path, and quantified the impact on the safety of nuclear power plants.