Experimental Study on PORV Break LOCA in PWR Plants

Abstract

Small break loss-of-coolant accident (LOCA) tests simulating a pressurizer power operated relief valve (PORV) break LOCA were performed using the EOS (Emergency of System) test facility. The break sizes were 0.25 and 0.88% of a guillotine break of a primary piping. The following major conclusions were obtained and the useful data and information for the verification of a computer code were obtained: (1) The pressurizer was almost full of water due to flooding limitation in the surge line of the pressurizer, when no water was in the hot leg piping. (2) The core was kept completely covered with two-phase mixture during the small break LOCA. (3) The core was sufficiently cooled down by reflux condensation in the steam generator even after the primary system natural circulation stopped. (4) After the depressurization of the primary system was stopped or when the depressurization rate of the primary system was small, the operator action to bleed the steam in the secondary system could steadily depressurize the primary system. (5) This operator action could resume the natural circulation in the primary system.