Japanese utility TEPCO says that a tentative analysis of water samples from the Fukushima Daiichi unit 4 spent fuel pool suggests that the majority of fuel is sound.

The analysis shows 2200 Bq/cm3 of iodine-131, 88 Bq/cm3 of cesium-134 and 93 Bq/cm3 of cesium-137. TEPCO admits that although radiation levels are higher than normal, it assumes the majority of the fuel is sound, although it cannot rule out the possibility that some fuel assemblies are damaged.

The news is significant because the spent fuel pond contains twice as much fuel as the other reactor spent fuel ponds because the active fuel in unit 4 was loaded into the pond for a maintenance outage that had begun before the tsunami struck. And the spent fuel pool sustained an explosion on 15 March. The sample was taken by a concrete pump with 62 metre boom on 12 April that is used to cool the pond; it sprayed 195 tons of water in it on 13 April.

Also, TEPCO has released its own calculation of the amount of iodine-131 released by the Fukushima Daiichi plant as on the order of 1×10^17 Bq, and the amount of caesium-137 released as on the order of 1×10^16. These levels are similar to the estimates by Japanese regulator NISA. TEPCO also said that there is no possibility of a further large release of radioactivity, because a stable system of cooling water injection is now in place.

TEPCO has also reported that it has built and tested a backup system for reactor water injection of units 1-3. Fresh water is collected from the Sakashita dam in a water tank. It is then pumped into a filtrate tank, and then into a freshwater tank, and from there pumped into the reactors. The backup system takes water from the filtrate tank to two redundant temporary tanks, from which it can be pumped into the reactors. TEPCO also plans to move a pump control switch panel and temporary diesel generators upland on 15 April. It also plans to build a new power line connection upland next week.

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