Fire engines were used in a desperate, and ultimately futile, attempt to pump water to cool overheating reactors during the early phase of the 2011 Fukushima No. 1 nuclear power plant disaster, Tokyo Electric Power Co. said.
According to a Dec. 13 report by the operator of the crippled facility, water was pumped in sufficient quantity to avert core meltdowns in the No. 1, No. 2 and No. 3 reactors, but much of it strayed into irrelevant pipes and ended up elsewhere.
In the report, TEPCO singled out 52 issues that had been left unanswered in its June 2012 investigation on the disaster triggered by the Great East Japan Earthquake and tsunami. The utility said it will find answers to those questions within two years.
The Dec. 13 report covered analysis results for 10 of those issues.
Equipment to cool reactor cores failed and quickly became unusable following the temblors at the Fukushima plant. For this reason, fire engines were connected via hoses to the piping system of the nuclear reactors to pump in water to cool them.
TEPCO said more than seven times the requisite volume of cooling water was pumped into the No. 2 reactor. But the water failed to cool it and the other reactors efficiently, and could not stop the core meltdowns in the No. 1, No. 2 and No. 3 reactors.
An examination of pipe diagrams and related equipment showed the pipes to the reactors had branches leading off to other areas and devices, such as condensation storage tanks. TEPCO concluded that too much of the pumped-in water leaked into those branches and never reached the reactors.
TEPCO officials said they knew as early as late March 2011 about those leakage routes.
"We should have shared the finding with the public in the belief it would help promote universal safety, but failed to do so," said TEPCO Managing Executive Officer Takafumi Anegawa.
The utility has installed electric valves in reactors at its idled Kashiwazaki-Kariwa nuclear power plant in Niigata Prefecture to avert a similar problem during an emergency, the utility said.
TEPCO also said the high pressure coolant injection (HPCI) system for emergency use lost part of its functions early in the No. 3 reactor, which was rocked by a hydrogen explosion.
The government's investigation committee said a manual shutdown of the HPCI system interrupted the cooling operations, which exacerbated the nuclear crisis.
But TEPCO took exception to that theory and said the HPCI system had already lost part of its functions by the time it was shut down manually, because nuclear fuel had become exposed very quickly following the manual shutdown.
That means nuclear fuel in the No. 3 reactor may be more damaged than an earlier study indicated. This suggests more melted fuel may have fallen outside the reactor pressure vessel, TEPCO said.
The utility added that the sharp pressure drop in the No. 3 reactor at 9 a.m. on March 13, 2011, was likely due to the activation of its automatic depressurization system, and dismissed the theory that the pressure dropped when a hole opened in a key component, such as the reactor itself.
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