Tokyo Electric Power Co. (Tepco) now says the meltdown of the Fukushima No. 1 nuclear power plant in March 2011 involved all the fuel rods in the affected reactor, causing them to fall to the bottom of the containment vessel.

Eight months after the massive tsunami caused the accident, Tepco said the meltdown had affected only about two-thirds of the rods. Its revised estimate, issued Aug. 6, said Reactor 3’s emergency cooling system stopped working six hours earlier than previously believed, and that the meltdown had begun between four and five hours earlier, as well.

The previous report, issued in November 2011, said the cooling system, called HPCI, had shut down at 2:42 a.m. on March 13, 2011. But the new study learned that the cooling system appeared to have lost its cooling function at about 8 p.m. the night before.

The new report also said all the melted fuel rods, not just the previously reported 63 percent, penetrated the reactor’s pressure chamber and containment vessel that holds the pressure chamber. They fell to the bottom of the containment vessel and melted nearly 27 inches down into its concrete floor.

Two days after the tsunami struck, at 9:25 a.m. on March 13, 2011, Tepco began using a fire truck to pump water into the No. 3 reactor in an effort to cool it down. Nearly 26 hours later, though, there was a hydrogen explosion in the building housing the reactor, blowing off the top of the structure.



Tepco says these new conclusions on when the accident began and the number of rods involved in the meltdown show that it will now be harder to extract the melted fuel and dispose of it.

Meanwhile, Bloomberg News calculates that Tepco appears likely to miss a deadline to remove a radioactive isotope linked to leukemia from the water stored at the ruined plant. Tepco President Naomi Hirose had promised Prime Minister Shinzo Abe that all the water would be cleaned by March 31, 2015.

When a Bloomberg reporter showed a Tepco spokeswoman the new estimate that more time is needed to rid the water of strontium because of equipment delays and a failed effort to stop radioactive contamination of nearby groundwater, Mayumi Yoshida replied that Tepco would do its best to get the job done on time.

Strontium can enter the food chain by depositing into the bones of fish, and further delays could prolong South Korea’s ban on imports of Japanese seafood.

By Andy Tully of Oilprice.com