Tokyo Electric Power Co. insisted July 28 that shaking caused by the March 11 earthquake did not rupture pipes of an emergency cooling system for the No. 3 reactor at the Fukushima No. 1 nuclear power plant.
Tokyo Electric Power Co. insisted July 28 that shaking caused by the March 11 earthquake did not rupture pipes of an emergency cooling system for the No. 3 reactor at the Fukushima No. 1 nuclear power plant.
TEPCO said it was "inconceivable" that the quake caused the pipes of the emergency "high pressure coolant injection" system to rupture and discharge a massive amount of vapor.
The company's announcement runs counter to its earlier analysis results released in May that indicated the possibility that the pipes were broken before the tsunami arrived.
The HPCI system is part of the emergency core cooling system designed to maintain the level of coolant water inside a nuclear reactor to prevent fuel rods from being exposed to air.
In the analysis results released in May, TEPCO said that during the initial phase of the crisis triggered by the March 11 Great East Japan Earthquake, a sharp drop in pressure occurred inside the reactor pressure vessel. That problem could be explained by water vapor leaking from broken pipes in the HPCI system, it said.
But in its latest analysis, TEPCO said no pipes were broken in the early stages because a worker entered the HPCI system's pump room on the first basement level on March 13, two days after the quake. If the pipes had been ruptured, hot discharged vapor would have filled the pump room and obstructed the worker's entry, TEPCO said.
To maintain stable operations of the HPCI system, the worker restricted the flux of coolant water and guided part of the water from the pump into a separate conduit. Those adjustments likely led to pressure variations inside the pressure vessel, TEPCO said.
The company did say, however, that on-site inspections of the damage were indispensable to reaching a final conclusion.
TEPCO the same day also released its analysis results on the impact of the shaking of the Great East Japan Earthquake on building and other major components of the No. 1 and No. 3 reactors.
Although the shaking exceeded maximum expected levels, simulations suggested that safety functions were retained at both reactors during and immediately after the earthquake, the report said.
An earlier report released June 17 contained similar assessments for the No. 2 and No. 4 reactors.
Tohoku Electric Power Co. on July 28 released analysis results on the impact of the Great East Japan Earthquake and an April 7 aftershock on all three reactors at its Onagawa nuclear power plant.
The tremors exceeded expectations, but remained below levels that could have disrupted functions of the reactors' major components, the report said.