TEPCO predicts cold shutdown at units 1, 2 and 3 by year-end

27 September 2011

As work continues to cover unit 1, TEPCO has predicted that it will be able to stabilise cooling of the damaged Fukushima Daiichi 1, 2 and 3 reactors by the end of the year, according to an interim progress report released in late September.

Work to cover Fukushima unit 1 continues
Work to cover Fukushima unit 1 continues

TEPCO defines the conditions of cold shutdown as a reactor pressure vessel bottom temperature of below 100°C 'in general', radioactivity release from the primary containment vessel is 'under control', and public exposure from additional radioactive releases are 'significantly held down.' As of 19 September, the RPV bottom temperature was 84°C at unit 1 (and temperatures are now being kept down below 100°C), 113°C at unit 2 and 91°C at unit 3. Core spray water injection (in addition to feedwater cooling) began at unit 3 on 1 September, and on 14 September for unit 2. Water injection amounts are 3.6m3/hr at unit 1, 7.6m3/hr at unit 2 and 12m3/hr at unit 3, according to TEPCO.

A frame for unit 1 has been completed, and panels are now being installed. Work to remove radioactive debris from the top of unit 3 began in September.

The current radioactive release rate at the site is 0.2 billion Bq/hr, consisting of 0.04 billion Bq/hr from the top of unit 1, the same from unit 2, an undisclosed amount from unit 3, and 0.13 billion Bq/hr in the breakwater area. A provisional estimate of site boundary exposure is 0.4 mSv per year.

Contaminated water treatment has reached its short-term goal of reduction to 3m above Ohama port levels, at which point the system can withstand heavy rain and prolonged outage without leaking, TEPCO said. It said that 95,000 tons had been processed as of 18 September.

TEPCO also plans to install a primary containment vessel gas control system in units 1-3 after core temperatures drop below 100°C. As nitrogen is injected into the PCVs, a similar amount of gas will be extracted, dehumidified, filtered, monitored and then discharged. The goal is to maintain PCV pressure at atmospheric levels. PCV (drywell) pressures as of 21 September were 0.1226 MPa, 0.112 MPa and 0.1015 MPa in units 1-3, according to Japan Atomic Industrial Forum's Atoms in Japan news service. (Standard atmospheric pressure is 0.1013 MPa.)

Mid-term plans are currently under review by the government regulator.

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