Safety evaluation guide on the emergency core cooling systems of light water power reactors

Issued by the Japan AEC, the safety evaluation guide is for evaluation of the functions and performance in design of the emergency core cooling systems (ECCS) of light water power reactors. ECCS are intended to suppress release of the FPs out of the Zircalloy claddings of the UO2, plus small amount of plutonium oxide, pellets at the time of hypothetical LOCAs. Requirements of the ECCS in this case are then the maximum cladding temperature below 12000C, the oxidized cladding thickness of less than 15%, the oxygen quantity due to cladding-water reaction of below integrity level of the reactor containment vessel, and decay heat removal of long-lived radionuclides. The guide is given broadly in three major phases of blowdown, reflooding, and heat-up. (Mori. K.)