The HPCI (High Pressure Coolant Injection System) is part of the emergency core cooling system but provides an important safety role. This system provides cooling to the reactor when certain failures have happened.
- Loss of normal core coolant inventory.*
* This can be due to an accident scenario or an operational scenario that causes the coolant level to drop to unsafe levels.
“The HPCI system is a single-train system that provides a reliable source of high-pressure coolant for cases where there is a loss of normal core coolant inventory. The HPCI system consists of a steam turbine-driven pump, valves and valve operators, and associated piping, including that from the normal and alternate pump suction sources and the pump discharge up to the penetration of the main feedwater line. For this study, the part of the main feedwater line from the check valve upstream of the HPCI connection to the reactor vessel, including the check valve, was considered part of the HPCI system. The steam turbine-driven pump includes all steam piping from the main steam line penetration to the turbine, and turbine exhaust piping to the suppression pool, valves and valve operators, gland sealing steam, and the turbine auxiliary oil system.” Source
A summary of reliability studies of the HPCI system by INL
A detailed review of the reliability issues of the HPCI systems and the Fukushima disaster by Peter Melzer