TEPCO outlines long-term plan

Phase one ends with the start of removal of fuel from the spent fuel pools (beginning with unit 4), and is targeted to end in two years (that is, by the end of 2013). In this operation, a fuel handling machine mounted above the pool would place spent fuel into containers under water, and then the reactor's overhead crane would lower the containers to ground level. Other tasks in phase one include maintaining on-site dose below 1 mSv/yr, maintaining stable reactor cooling and accumulated water processing, starting fuel debris removal R&D and decontamination and starting radwaste processing and disposal R&D.

Phase two ends with the start of removal of fuel debris—solidified material from melted fuel. This work is targeted to end in 10 years (that is, by the end of 2021). Other tasks in phase two include completion of spent fuel removal (unit 3 would be the second pool emptied), preparations for fuel debris removal, including decontaminating reactor building interiors (Figure 1, at right), fixing PCV leaks (2), continuing stable reactor cooling, completing processing of accumulated water, continuing fuel debris removal R&D (3), flooding PCV and RPV and removing vessel head (4), and RPV and fuel sampling (5).

Phase three ends with total decommissioning of the site, in 30-40 years (by 2041-2051). Other tasks in phase three include completing fuel debris removal (6) (in 20-25 years, that is by 2031-2036), and implementing radioactive waste processing and disposal.

For now, however, the document says that TEPCO is working to a three-year plan from a safety directive produced by the government regulator Nuclear and Industrial Safety Agency called ‘Ensuring mid-term safety’.

Interim analysis
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TEPCO has also published an English-language version of summary of an interim internal analysis of the Fukushima incident.

The original interim analysis, dated 2 December, reviewed the main facts of the 11 March earthquake and tsunami, and its effects on Fukushima Daiichi and Daiini.

The report said: “In the Fukushima accident, the destruction caused by the tsunami resulted in the loss of almost all equipment and power source functions expected to be activated in case of accidents, including those for AM [accident management] measures prepared together with the government. As a result, workers on the site were forced to adapt to sudden change of circumstances such as injecting water into the reactors using fire engines, and the accident management became extremely difficult. The situation on the site was far beyond the originally estimated accident management conditions, and as a result, the expansion of the accident could not be prevented under the framework of the prepared safety measures.”

The report has outlined eight countermeasures to prevent such an incident happening again.

1. Installation of tidal embankment, boards, and wall and flood protection of door and penetrations

2. High-pressure cooling water injection facilities (deployed within one hour)

3. Depressurizing equipment, including spare N2 tanks and batteries (deployed within 4-8 hours)

4. Low-pressure water injection facilities consisting of an emergency system, a make-up water condensate system (MUWC) and a fire protection system (deployed within 4-8 hours)

5. Heat removal/cooling including (a) PCV venting (within 1-2 days); (b) heat removal via shutdown cooling mode that uses seawater as a cooling source (within 3-7 days) and (c) heat removal from spent fuel pool (within 7-10 days)

6. Ensuring power supply to the monitoring instruments (deployed within 1 hour)

7. Mitigation measures following reactor core damage such as preparation to drill holes in the roof or opening blow-out panels to prevent accumulation of hydrogen

8. Auxiliary equipment (for power, lighting, debris removal) required to achieve the previous seven countermeasures

Four other mid-term and long-term technical issues will be considered separately, TEPCO said (see www.neimagazine.com/interim).

This article was first published in the February 2012 issue of Nuclear Engineering International magazine