Fukushima watch 2011-04-27

Tepco is preparing for a “wet tomb” for unit 1 and 3 of Fukushima 1. It stepped up its water injection for unit 1 from 6 m3/h to 14 m3/h today to test for leaks. It is using robots to visually inspect the inside of the reactors for signs of water leaking.

By allowing water from the reactor pressure vessel (RPV) to overflow into the containment that surrounds it, almost all of the RPV will be immersed in water, which will carry away heat from the fuel rods inside the RPV through conduction. 7,800 tons of water will be injected. If the water starts leaking from the containment, the plan will have to be abandoned. Concern has been raised how the extra weight would affect the seismic stability of the building in the event of another major quake.

Radioactive water has been found in the basement of the turbine building of unit 4, which was shut down at the time of the tsunami and does not have any fuel loaded in its core. The water is assumed to have leaked across from adjacent unit 3.

Tepco has released a radiation map for the Fukushima 1 plant, showing known radiation “hot spots” around the site.

Power companies operating nuclear power stations in Japan have deployed vehicle-mounted mobile backup generators at their plants, but in many cases their capacity is too small to replace the fixed backup generators such as the ones that failed in Fukushima 1. Surprizingly, they don’t seem to be in much of a hurry to address that safety problem: Japan Atomic Power Co. is quoted by Kyodo as trying to purchase three generator trucks by March 2012 while Hokkaido Electric Power Co. wants to buy a second generator vehicle for its Tomari power station “within two years”.

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