Meltdown of Three Units Suspected at Fukushima Daiichi

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Researched by Industrial Info Resources East Asia (Kofu-shi, Japan)--Following last week's notification of the meltdown of Unit 1 at Fukushima Daiichi nuclear power station, Tokyo Electric Power Company Incorporated (TYO:9501) (TEPCO) (Tokyo) suspects that similar damage has taken place at units 2 and 3. In immediate response, the Fukushima exclusion zone was widened to at least 45 kilometers, and rescue operations have begun evacuating residents within the widened exclusion zone to neighboring villages and towns.

The presence of a leak in the reactor pressure vessel of Unit 1 indicated that meltdown occurred after melted fuel settled at the bottom of the pressure vessel and created one or more holes. This leak, as well as faulty pipes in the containment vessel, has allowed for the continuous escape of water used in cooling efforts and has lead to the collection of more than 4 meters of contaminated water in the basement of the unit housing. TEPCO and other involved organizations have been working to keep reactors and fuel pools cooled with the use of mobile pumps and water lines, while attempting to remove contaminated water. Constant cooling efforts have limited the dispersal of radiation.

At the end of April,TEPCO updated information regarding the extent of reactor fuel damage at Fukushima Daiichi; the amount of damaged reactor fuel in Unit 1 was revised down from 70% to 55%, while the amount of damage to the reactor fuels in units 2 and 3 was revised up to between 35% and 30%, respectively. According to TEPCO data, the meltdown of Unit 1 occurred approximately 16 hours after the tsunami struck the power station. The March 11 earthquake, however, is suspected of causing initial damage to pipes and pressure vessels. TEPCO believes that the meltdown of units 2 and 3 occurred within the same time frame in light of water leakage situations similar to that of Unit 1. Water is suspected of leaking from the pressure vessels of units 2 and 3, leading to the basement flooding of those units as well.

Two weeks ago, TEPCO was able to install new monitoring equipment as well as a ventilation system in Unit 1 that allowed workers to enter the building in order to conduct radiation checks. The idea was to lower the amount of radiation to extend visits to the unit in order to hasten cold shutdown. After the new monitoring equipment was installed, TEPCO disclosed that despite reactor cooling efforts, water levels in the pressure vessel remained below that of safe operation, adding to the suspicion of a leak in the pressure vessel. The utility company is now being forced to reevaluate its original plans for cold shutdown.

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