Analysis of severe accident by beam tube break in 30 MW pool type research reactor with U3Si fuel

Abstract

A consequence of a beam tube break accident (BTLOCA) was analyzed for a 30 MW pool-type research reactor with finned fuel rods composed of U3Si and aluminum. The thermal hydraulic behavior, the core relocation, and the release of fission products were analyzed for the BTLOCA using MELCOR. The beam tube is a penetration through the pool wall to the reactor core for transporting the neutron source, therefore the BTLOCA induces continuous pool water loss even after the fuels are exposed above water if there is no countermeasures such as emergency water supply system (EWSS). The fuel then melt down and relocate to the lower plenum, during which fission products are released from them. The flap valve opening, which provides the flow path between the reactor pool and the reactor structure assembly (RSA), affects the time to melt the fuel and the following fuel relocation. Fission products were released from the molten fuel by the accident, nevertheless, the amount of them leaked out to the environment were negligibly small because the building pressure is kept low during the accident.