Computational Studies of Thermal Hydraulics in a New Integral Reactor Plant VVER-I with Natural Circulation

In the present-day conditions under which the nuclear power industry is developed, a need arises to diversify the designs of new nuclear power plant units, which should differ from the previously constructed ones by featuring flexibility to the customer requirements and by using safety systems based on fully passive safety assurance principles. In 2022, specialists of Experimental and Design Organization (OKB) Gidropress commenced activities on elaborating the draft design of a new integral pressurized water-cooled reactor plant VVER-I with natural circulation of coolant for a basic thermal capacity of 250 MW. The design incorporates passive safety systems able to provide reliable heat removal from the core under the conditions of a long-term NPP blackout and without the operator’s participation. The article presents the results obtained from thermal and fluid dynamic computations of the new reactor plant carried out using the KORSAR/GP code that has been certified for safety analyses. A reactor plant thermal-hydraulic model, which can be used for computations of stationary normal operation conditions and, subsequently, also for simulating the accident scenarios evolvement dynamics, has been developed and tested. Computations carried out using the system code have confirmed a correct choice of the reactor’s main geometric parameters and the steam generator’s heat-transfer surface for operation at the nominal power. Based on the computation results for optimizing the design, it is proposed to use a jacketed steam generator, which will make it possible to exclude stray coolant leaks in bypass of the heat-transfer surface. It is shown that the newly developed reactor plant has a significant potential for increasing the thermal power capacity up to 400 MW without introducing fundamental changes in the design. The study results can be used in designing new VVER reactors with natural coolant circulation, and also in the development of passive safety systems.