Japanese utility Tepco has completed its emergency reactor management plan for the Fukushima Daiini nuclear power plant.
Although this four-BWR-unit site was not as severely damaged by the earthquake and tsunami as the Fukushima Daiichi plant to the north, it did lose power and has remained shut down since March.
Tepco has now completed emergency countermeasures to safeguard the reactor core and fuel assembly in case of loss of AC power, loss of reactor seawater cooling and loss of spent fuel pool cooling in case of a tsunami. It has submitted its report of this work to the Japanese government.
First, it carried out an emergency inspection after the 11 March tsunami, now complete. Second, it has set up a new emergency response plan, and trained site workers. Third, it has established a new protocol to supply emergency backup power via a truck-mounted genset, and performed practice drills. Fourth, it has established a new emergency heat removal function in emergencies, by installing a compressed gas tank as a backup actuation method for the drive of the primary containment vessel vent valve, in the absence of AC power. Fifth, it has designed a procedure using fire engine pumps to inject cooling water into the reactor, and the spent fuel pond, in emergencies. Sixth, it has built up artificial embankments and sandbagged doors of critical safety buildings to protect them against another tsunami. It has also delivered excavators to remove rubble from the site.
Further work to achieve cold shutdown will aim make safety-important buildings watertight, install large-capacity power supply for cooling systems, and enhancement of monitoring and communication equipment.
Work at Fukushima Daiichi
Meanwhile, at Fukushima Daiichi, workers have installed new reactor cooling pumps for units 1, 2 and 3 on an upland location, and testing has begun.
Preparation for work to construct an alternative cooling system for the unit 2 spent fuel pond has begun; installation of the main components is expected to take a week, after which testing will begin.
Workers entered units 2 and 3 of the damaged Fukushima Daiichi nuclear power plant, each time for a quick 10-15 minute survey. Three puddles were discovered in the unit 2 building ground floor. The building was physically difficult to walk around, as it was hot and humid. For the unit 2 survey, each of the four workers' total dose ranged between 3.3-4.3 mSv. The unit 3 survey, intended to check conditions to prepare for nitrogen injection, was cut short (to 10 minutes) because of high dose. Their total dose was between 2-3 mSv, but the dose rate was 50-170 mSv/hr.
Workers began pumping puddled water from the unit 3 turbine building basement. A unit-by-unit analysis of the total extent of puddled water estimates that a total of 100 000 m3 of water has pooled in Fukushima Daiichi units 1-6 reactor buildings, turbine hall basements and trenches. According to the figures, the largest pool is the unit 2 turbine basement (13 000 m3), and unit 2 is the most flooded of all (25 000 m3). The least flooded is unit 5 (300 m3).
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