Temperature rises at Fukushima Daiichi unit 4 spent fuel pool

26 April 2011

The water temperature of the Fukushima Daiichi unit 4 spent fuel pool has been approaching boiling over the past week. However, periodic water injection with a concrete pump has reduced water temperatures.

Reactor-by-reactor, system-by-system summary from JAIF as of 26 April
Reactor-by-reactor, system-by-system summary from JAIF as of 26 April; yellow indicates abnormal/unstable; red means damaged/nonfunctional

The spent fuel pool water temperature was 90°C on 22 April before a spray of approximately 46 tons of water. It rose again to 83°C before spraying 140 tons of water on 23 April, and 66°C after. It rose to 86°C before spraying 165 tons of water, and 81°C after, according to a summary from the Japan Atomic Industrial Forum. Because the unit 4 reactor was shut down at the time of the earthquake and tsunami on 11 March, its fuel pool contains not only spent fuel, but also the reactor's current fuel load (a total of more than 1500 fuel rods). TEPCO was planning to inject 210 tons of water into the pool on 25 April, according to a report from Japanese newswire NHK, republished by JAIF. The report adds that concerns about the bearing strength of the building, which has been weakened by the earthquake, had previously limited the amount of water injection. It is now planning to install concrete pillars beneath the pool to stabilise it in case of aftershocks.

In other news, the temporary 6.9kV emergency power source went offline for three hours on 25 April as workers connected the high-voltage power panels at units 1&2 to that at units 5&6. Emergency reactor cooling pumps were switched to a temporary diesel generator. NHK reports that the work is intended to secure electricity supply in the case of another earthquake; in case any one of three outside sources of power is cut off, another source can be used.

Also, JAIF reports on the convening of the first meeting on compensation for nuclear damage on 15 April. The panel is led by law professor Yoshihisa Nomi of Tokyo's Gakushuin University. Because the accident is caused by a natural disaster, the government is likely to pay out a maximum of JPY120 billion per company, or $1.46 billion. Guidelines are due in July.

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