Comparative Safety Assessment of Supercritical Water-Cooled Nuclear Reactors (VVÉR SKDI)

The overwhelming majority of currently operating nuclear reactors are water-cooled. A further advancement of this trend is associated with the development of supercritical water-cooled nuclear reactors (SCWR). The work on developing SCWR is being conducted within the scope of the Generation IV International Forum. In Russia, one of such developments is related to the V-670 VVÉR SKDI reactor unit (RU), the concept of which was proposed by the NRC "Kurchatov Institute" in the 1990s. The VVÉR SKDI is a shell-type water-cooled reactor, which utilizes supercritical water and features an integrated primary circuit layout with natural coolant circulation. These features provide a high level of RU safety and make it possible to eliminate a number of safety systems (SS), which are present in the design of modern VVÉR reactor units. This paper offers a safety analysis of the V-670 VVÉR SKDI unit in comparison with the V-392M unit for a well-studied NPP-2006 project. A description of potential accidents and safety systems designed for the V-392M unit is provided. A detailed description of specific featured of the VVÉR SKDI reactor is presented, and their effect on reactor safety is analyzed. In addition, a review of potential issues in the core zones of the foreign single-circuit SCWRs is performed. Such reactors are characterized by tight fuel rod spacer grids and high operating temperatures of the fuel rod cladding, which could interfere with flooding of the active zone and result in rapid cladding temperature growth during LOCA. Such problem can be avoided in the VVÉR SKDI reactors, which have a moderate level of core temperatures and wider spacer grid. The paper summarizes the advantages of V-670 RU and discusses the challenges that must be resolved in order to advance the development of the VVÉR SKDI reactor design.