A worker at the tsunami-hit Fukushima No. 1 nuclear station manually stopped a coolant injection system in the plant‘s No. 3 reactor following the disaster for fear that the reactor would be damaged and lead to a radiation leak, its operator said. Plant operator Tokyo Electric Power Co. (TEPCO) has defended the worker’s judgment as appropriate after analyzing the sequence of events and releasing its findings at the order of its government regulator, the Nuclear and Industrial Safety Agency.
The reactor core isolation cooling (RCIC) system of the No. 3 reactor stopped at 11:36 a.m. on March 12, the day after the plant was hit by a massive tsunami triggered by the Great East Japan Earthquake, causing the water level in the reactor to decline.
In response, its high-pressure coolant injection (HPCI) system, powered by a battery, was automatically activated.
However, the pressure in the reactor subsequently lowered below the standards specified by its operation manual, and vibrations increased. The worker in charge stopped the HPCI system and decided to switch to manual injection of water for fear that the trouble could cause radioactive substances to leak from the reactor, according to the utility.
However, a valve to lower the pressure inside the reactor before water was manually injected would not open because all external power had been lost. As a result, water could not be injected into the reactor, causing a meltdown of the core.
The government’s fact-finding panel on the nuclear crisis earlier confirmed that plant workers decided to switch off the HPCI system at their own discretion.
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