Electrical utility Tepco has outlined its plans for restoring the damaged Fukushima Daiichi nuclear power plant. It estimates that not until July 2011 will it be able to bring radiation doses into steady decline. By between October and December 2011 it expects to have the release of radioactive materials under control, and to be able to hold down radiation dose significantly.
The three-month target of reaching declining radiation dose, called step 1, relies on two current activities: the prevention of hydrogen explosions, and prevention of release of contaminated water. The risk of hydrogen explosions increases because of steam condensation caused by injecting fresh water into the reactor, Tepco said. It will continue to inject nitrogen gas into containment to reduce the concentrations of hydrogen and oxygen below the limit of inflammability. As of 14 April, it had injected 5500 m3 of nitrogen into the unit 1 containment vessel. To deal with contaminated water, Tepco is working to acquire more storage and also processing facilities. As of 15 April, Tepco reported that the central waste treatment facility, capacity 25000 tons, had finished its examination and was prepared to receive contaminated water from turbine buildings and the trench.
Less immediate targets, called step 2, will take from six to nine months to achieve, Tepco said. They include installing temporary covers for the buildings, and a seismic support structure for the unit 4 spent fuel pool in particular, of which the walls have been damaged.
As part of the recovery analysis, Tepco summarised the current state of the plant, system by system, and summarised the countermeasures it was currently performing, and planning. It has divided these into different categories.
Current status of reactor cooling:
(Units 1 to 3) Cooling achieved by water injection while there is partial damage to fuel pellets.
(Units 1 to 3) High likelihood of small leakage of steam containing radioactive materials through the gap of PCV [primary containment vessel] caused by high temperature.
(Unit 2) Large amount of water leakage, indicating high likelihood of PCV damage.
Secured multiple off-site power (1 system each from Tepco and Tohoku EPCO) and deployed backup power (generator cars /emergency generators)
Current status of spent fuel pond cooling:
Fresh water is injected from outside for Units 1, 3, 4 and through normal cooling line for Unit 2.
Confirmation of release of radioactive materials from the pool
Walls of the building supporting the pool have been damaged.
Current status of mitigation of contaminated water:
Leakage of high radiation-level contaminated water assumed to have originated from Unit 2 reactor occurred, but was subsequently stopped.
Leakage and accumulation of high radiation level contaminated water at unit 2’s turbine building, vertical shafts and trenches.
Increase of storage volume of water with low radiation levels.
High likelihood of underground water around the building (sub-drainage water) to be contaminated.
Current status of mitigation of aerial/earth release of contamination:
Debris is scattered outside the buildings and radioactive materials are being scattered.
Current status of monitoring and decontamination:
Monitoring of radiation dose inside and out of the power station is carried out. (Seawater, soil and air sampling at 25 sites inside the boundary and 12 locations outside).
Regular updates may be found on the website of our sister journal, Nuclear Engineering International, reachable on <www.neimagazine.com> or by clicking on the link in the navigation bar to the left of this page.
The following sites are also posting continuing updates:
<http://www.tepco.co.jp/en/index-e.html>
<http://www.iaea.org/>
<http://www.jaif.or.jp/english/>
<http://bravenewclimate.com/2011/03/15/tepco-reactor-status/>
<http://www.world-nuclear-news.org/>
<http://www.kantei.go.jp/foreign/index-e.html>
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