Michele Kearney's Nuclear Wire

Major Energy and Environmental News and Commentary affecting the Nuclear Industry.

Monday, March 21, 2011

Fukushima Units 5 and 6 in Cold Shutdown, Progress Reported in Restoring Power to Other Units

Blog Post: Fukushima Units 5 and 6 in Cold Shutdown, Progress Reported in Restoring Power to Other Units

This weekend saw a few positive developments at the Fukushima Daiichi nuclear plant, where crews continue to spray spent fuel tanks and work to restore power to damaged reactors.
Japan’s Nuclear and Industrial Safety Agency reported Sunday that units 5 and 6 are now in cold shutdown. Additionally, an AC power cable was extended to the units on Sunday. Neither was running March 11 when a magnitude 9 earthquake triggered a chain of accidents at the plant, but limited backup power made decay heat in their reactors and spent-fuel tanks a concern.
Fukushima Daiichi March 17Crews also made progress in efforts to restore AC power to the more heavily damaged reactors at the plant. Unit 2 has received power, and as of Sunday crews were running checks on electrical systems. A survey to lay cables to units 3 and 4 also was completed, with external power scheduled to be hooked up today.
The extent of damage from explosions in units 1 though 3 and a fire in unit 4 – and how that will affect efforts to restore power – remains unclear. When the power line was extended to the plant last week, officials indicated components of the reactors’ cooling systems may need to be replaced after salt water was used to cool them over the course of last week.
While engineers work to restore electric systems necessary to control the reactor cores, spraying from military, fire and police trucks continued efforts to cool spent-fuel tanks that had also lost their cooling systems. Over the weekend, crews continued to spray water into the tanks at units 3 and 4. NISA also indicated 40 tons of seawater was injected in unit 2’s spent-fuel tank starting Sunday.
The Wall Street Journal quoted the Japanese defense minister as saying temperatures in all tanks containing spent fuel have fallen below 100 C. NISA reported temperatures inside the tanks at units 5 and 6 of 35.1 C and 28 C Sunday, respectively.
Reports indicated radiation readings directly outside the damaged reactors had fallen somewhat after the spraying. Radiation monitors outside the evacuation zone continue to show levels within healthy limits, although Kyodo reported a town 25 miles from the plant has been advised by the health ministry to stop drinking tap water after testing found levels of radioactive iodine three times the regulated limit. There were also reports of slightly elevated radiation detected in crops harvested near the plant.
Next steps at the reactor may include debris removal using Japanese tanks and water spraying with a concrete truck that can pour water from a higher angle, Kyodo news reported.

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