Heat transfer coefficient measurement for outer wall of the reactor vessel lower head under IVR-ERVC condition

Abstract

IVR-ERVC (In-Vessel Retention by External Reactor Vessel Cooling) is one of the severe accident management strategies, and removes the decay heat through the reactor vessel lower head by supplying cool-ing water to the lower head. Therefore, estimating HTC (Heat Transfer Coefficient) of the outer wall is im-portant to evaluate the ERVC heat removal capability. From previous researches, severe accident analysis code (MAAP and MELCOR) used Rohsenow correlation to calculate the HTC, and SBLB experiment was conducted to measure the HTC. However, the Rohsenow and SBLB experiment couldn’t consider effect of the reactor vessel lower head surface geometry (especially radius curvature) and material. These geometry and material of heater could affect the HTC. Accordingly, in this research, the HTC measurement experi-ment was conducted with SA508 heater which had 2.5 m radius curvature. This research had two main objects. First was experimentally producing the HTC database with SA508 heater which has 2.5 m radius curvature. Second was suggesting the HTC correlation by modifying the existing correlation. To simulate the flow boiling condition of ERVC, water loop was prepared, and the loop controlled working fluid (DI water) temperature and mass flux. The reactor vessel lower head outer wall was simulated by the SA508 plate heater. The experiments were conducted at four angular range to cover whole reactor vessel lower head (from bottom ($0^\circ$) to top ($90^\circ$)). The heater surface temperature was meas-ured by IR camera, and finally the HTCs were calculated. LLOCA was used as base accident, to determine working fluid inlet condition, mass flux and the heater heat flux. In this research, the HTCs were measured at 10-$90^\circ$ of the heater inclination angle, 300-$500 kg/m^{2} s$ of the working fluid mass flux and 100-$950 kW/m^{2}$ of the heater surface heat flux. Modified Chen correlation was used to develop the HTC correlation.