Natural Convection Core Cooling in MTR Research Reactors

This paper is focused on the evaluation of core cooling after a loss of offsite power that is accompanied with or without the functioning of the natural convection valve. The reference reactor is IAEA 10 MW MTR pool type Research Reactor (RR). The best-estimate thermal hydraulic system code RELAP5 that is used widely in the safety analysis of power reactors is used in the present analysis. The results show that the natural convection core flow established after the opening of the natural convection valve (NCV) cools down the fuel clad and maintain its temperature far from the onset of nucleate boiling temperature. The malfunction of the natural convection valve initiates core internal circulation loop directly proportional to the size of core bypasses. In addition the clad temperature in both core channels attains high values. An essential intervention from the operator to immediately open NCV should be taken.