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High Pressure Coolant Injection (HPCI) System
The HPCI is used in BWR-2 through BWR-4 boiling water reactor designs. 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.
The HPCI system is actuated by either a low reactor water level or a high drywell pressure. Initially the system operates in an open loop mode, taking suction from the condensate storage tank (CST) and injecting water into the reactor pressure vessel (RPV) via one of the main feedwater lines. When the level in the CST reaches a low-level setpoint, the HPCI pump suction is aligned to the suppression pool. To maintain RPV level after the initial recovery, the HPCI system is placed in manual control, which may involve controlling turbine speed, diverting flow through minimum-flow or test lines, cycling the injection motor-operated valve (MOV), or complete stop-start cycles. The HPCI system is also manually used to help control RPV pressure following a transient. ” NRC.
HPCI pump used for high pressure emergency coolant injection to the reactor, this pump is turbine driven by steam
Source: BWR Plant Photos – inside and outside
Various definitions of the term Ultimate Heatsink
September 27, 2012
“Loss of ultimate heat sink. In addition to disabling the emer-
gency diesel generators, the tsunami disabled Fukushima’s
“ultimate heat sink”—the systems, such as seawater pumps
and motors, used to remove heat from the reactor coolant
system and to cool emergency systems throughout the plant
following an accident”
Source: Union of Concerned Scientists, pp 12 “U.S. Nuclear Power Safety One Year after Fukushima” David Lochbaum | Edwin Lyman
The existence of the following device is allowed in the NRC definition of “Ultimate Heatsink”. The Torus acts the Heatsink for the injected coolant in this particular part of the Emergency Coolant. In addition, other steam turbine powered pumps introduce and propel coolant through other backup loops. Condensers located in the reactor buildings for one such additional emergency coolant loop.
The tragedy is the valves in the coolant pipes these and similar devices in the reactor buildings rely on are controlled by low current DC electricity which the emergency could supply but does not. As a result these critical solenoids run of batteries in emergency operation. The life and survivability of the batteries time limit the operation of such emergency backup cooling such as that provided by the High Pressure Coolant Injection units. The alternate cooling circuit has it own “heat sink” in the reactor buildings. In emergency settings when the emergency systems should be running, there are more than one “heat sink” . There is more than one pump.
The ECCS did not work because the valves are not provided secure DC voltage.
But at the design stage they should have been, for the ECCS is required to be able to operate during emergency.
It is not beyond intelligent design to provide integral inviolate power to the solenoids, as is in fact supplied to the HCPI pumps.
The 50 cent concept of uninterruptible power supply was not applied.
The maximum time any of the low current DC solenoid circuit batteries lasted for was 70 hours (American Nuclear Society). No matter how that time limit is justified, it is insufficient, for the ECCS as a whole is required to last for as long as needed. The ECCS system, like any other system, is as reliable as its weakest link. If time defines the outcome, why design an ECCS that is time limited as dictated by the vulnerability of batteries? If it were a plane it would not be allow to fly. Why was not the reactor used to power itself and its systems. Why rely on the grid in emergency when in the first instance the reactor power the grid? There is a steam turbine in the reactor buildings. It is there to power the emergency coolant pumps. Why can’t it also include DC generation for the pump valves? The pumps need open pipes after all.
Other wise the thing fails catastrophically. Now, I don’t like reactors. But I dont want them to blow up. One would have thought the companies that made these things wouldn’t want catastrophic failure either.
How long it took TEPCO to disclose to the Prime Minister that the emergency cooling system could not be switched on and maintained I do not know.
This failure sequence was foreseen in the late 1960s, debated in the 1970s and fudged by the nuclear industry at that time.