A concrete pump has poured 150 tons of seawater into the Fukushima Daiichi unit 4 spent fuel pool.
The pump's 58m boom reaches from ground level up to the pool. That amount corresponds to about 10% of the pool's total volume of 1425m3. The operation was carried out by 12 workers and took three hours.
The unit 4 spent fuel pool is the most critical of all the Fukushima Daiichi spent fuel pools. Because Unit 4 was shut down at the time of the tsunami, its spent fuel pool contains both 783 spent fuel assemblies, plus 548 fuel assemblies unloaded from the reactor. Its total inventory of 1331 fuel assemblies is greater than the inventory of the spent fuel pools of units 2 and 3 combined.
Although unit 5 and 6 were also shut down at the time of the tsunami, and so also have large inventories in their spent fuel pools, TEPCO staff were able to restart residual heat removal system pumps on 19 March.
At almost three times the volume of the other spent fuel pools, the common spent fuel pool has the greatest number of fuel elements, 6375 out of 6840; but TEPCO reported that water in the pool was secured on 18 March. In addition, this pool is likely to house the oldest, and hence least reactive, fuel.
FilesReactor-by-reactor, system-by-system summary from JAIF on 24 March