Almost nine hours later, an announcement from the Ministry of Economy, Trade and Industry said that three of four mobile power supplies had arrived at Fukushima Daiichi and cables were being set up to supply emergency power. Other power modules were in transit by air.
However, pressure inside the containment of unit 1 had been steadily increasing over the time that emergency core cooling systems had not been active. Tepco reported at 2am that pressure had increased to around 600 kPa, compared to normal operating levels of 400 kPa.
The company then announced a decision to reduce the pressure within containment "for those units that cannot confirm certain levels of water injection" by the safety systems. "We will endeavor to restore the units and continue monitoring the environment of the site periphery."
An International Atomic Energy Agency announcement at 4.20am confirmed the work to restore power using mobile power supplies. It noted the increase in pressure at unit 1 and said that this would be relieved by a controlled venting operation, "which will be filtered to retain radiation within containment."
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