A numerical study on convective heat transfer characteristics at the vessel surface of the Korean Next Generation Reactor

The Korean Next Generation Reactor(KNGR) is a pressurized water reactor adopting Direct Vessel Injection(DVI) to optimize the performance of Emergency Core Cooling System(ECCS). In a certain accident, however, Pressurized Thermal Shock(PTS) of the vessel due to the sudden contact with the injected cold water is expected. In this paper, an accident of Main Steam Line Break(MSLB) has been numerically investigated with direct vessel injections and an increased volume flow rate in some cold legs. Using FLUENT code, temperature distributions of the fluid in the downcomer and of reactor vessel including the core region have been calculated, together with the distribution of Convective Heat Transfer Coefficient(CHTC) at the cladding surface of the reactor vessel. The result shows that some parts of the core region of the reactor vessel have higher temperature gradient expressing higher thermal stress