ICONE23-1647 ABWR4 : SPENT FUEL POOL AND CORE COOLING DURING REFUELING OF THE INNOVATIVE ABWR UNDER A SBO

Abstract

iB1350 stands for an innovative, intelligent and inexpensive BWR 1350. It is the first Generation III.7 reactor after the Fukushima Daiichi accident. The iB1350 has the spent fuel pool in the operating dome. During normal operation the spent fuel pool is cooled by the fuel pool cooling system (FPC). If a SBO occurs, the alternate feedwater injection system (AFI) makes up the spent fuel pool. Steam from the spent fuel pool is released through the external venting system (EVS). During refueling outage, however, the PCV head and the RPV head are removed. The reactor well is flooded by refueling water and connected to the spent fuel pool. If a SBO occurs in the refueling mode the severe accident feed water system (SAFWS) makes up the refueling water with the S/P water. The overflowing water is collected into the drain pit on the operating floor. The water in the pit is returned to the S/P via the drain pipes. Decay heat of the core fuels and the spent fuels are both transferred to the S/P. In the long term the S/P starts boiling. Then the innovative passive containment cooling system (iPCCS) initiates cooling of the S/P. In this way the integrity of both the core fuels and the spent fuels is assured. If the SAFWS is also lost core melt might occur. The AFI, however, makes up the spent fuel pool and the cooling of the spent fuels is still maintained. In order to cope with this situation the operating dome is enhanced to withstand pressurization and confine FP. These enhancements are easily achieved because the operating dome is made of steel and concrete composite (SC). The enhanced containment vessel is named Mark W^+ containment. It has also a filtered dome venting system (FDVS) connected to the operating dome. If boiling of the refueling water starts steam is vented to the environment via the EVS. The oxygen in the operating dome is purged by the steam. Then if fuel damage starts the EVS is closed and the FDVS takes over. Hydrogen is purged to the environment through the FDVS. After shutdown noble gases and iodine are already well decayed and operation of the FDVS does not cause any excessive dose. After the hydrogen purging is finished the FDVS is closed. Then the connecting venting pipe is opened and the iPCCS takes over the cooling of the Mark W^+ containment. Let it go. Let it go. The core never bothers it anyway.