Protection against high-energy line breaks in WWER power plants

During international investigations of the safety status of the Russian PWR plants (WWER), the protection against the effects of high-energy line breaks was considered. Especially, in the field of protection against local pipe break effects, the WWER plants showed some relevant shortcomings. The most critical area of the plants is the main steam and feed water system compartment located between the reactor containment and the turbine hall. The modernization programs of several nuclear power plants (NPPs) with WWER bring efforts to limit the effects due to postulated high-energy line breaks. Within such programs, Siemens has carried out detailed investigations on the WWER-440/ 213 NPP Mochovce Units I and 2, and on the WWER-1000/320 NPP Kozloduy Units 5 and 6. The methodology of the investigations is presented and some of the most important measures are shown in this paper. It can be concluded that, due to the performed analyses and the implemented protection measures, main steam line and main feedwater line breaks at the postulated break locations will not lead to consequential failures beyond the defined design basis for accident mitigation.