Closed-loop circulation starts at Fukushima Daiichi

28 June 2011

TEPCO has begun injecting decontaminated water into units 1, 2 and 3 of the Fukushima Daiichi nuclear power plant.

Closed-loop cooling at Fukushima Daiichi
Treated water is now flowing to units 1, 2 and 3, and units 2 and 3 are returning contaminated water to the treatment system

The decontaminated water comes from the new treatment system installed on site. Currently, a total of 13 m3/hr of treated water is being injected: 3.5m3 for each of units 1 and 2, and 9m3 for unit 3. (In addition, 3m3/hr of water is pumped from the existing water source, the filtrate water tank). Both units 2 and 3 (though not unit 1), are returning water to the system via the centralised radioactive waste treatment facility tanks.

Unit 3 is receiving more cooling water because it is likely the hottest reactor. According to new temperature data, unit 3 feedwater nozzle temperature was 154.6°C, RPV temperature of 129.1°C as of 27 June. Unit 1 readings were 115.9°C and 100.8°C; unit 2 readings were 109.7°C and 119.5°C, respectively.

The start of closed-loop cooling water circulation is a major breakthrough for the site, which has been producing hundreds of tons of contaminated water per week to compensate for the reactors' decay heat.

Since the treatment system started up on 17 June, TEPCO has confirmed that it removes more than 99.99% of caesium; it expects it has a decontamination factor of 10,000-100,000. Over its first three days of operation, it filtered 2500 tons of water.

A sample of unit 1 spent fuel pond water has found higher-than-normal levels of activity-it contains about 1.8 million times as much caesium 137 as before the incident. However, TEPCO concludes that the majority of the fuel in unit 1 is undamaged, and the radioactivity came from external sources, such as contaminated steam and dust.

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