Strong aftershocks have added another layer of problems for workers trying to stabilize the crippled Fukushima No. 1 nuclear power plant and forced a shift in the plant operator's emergency power setup.
Strong aftershocks have added another layer of problems for workers trying to stabilize the crippled Fukushima No. 1 nuclear power plant and forced a shift in the plant operator's emergency power setup.
Tokyo Electric Power Co. workers were checking to see if the recent aftershocks damaged pipes or cracked the walls and floors in areas containing water contaminated with high levels of radiation, including the central waste processing facility.
But the main concern is if the aftershocks will sever power to pumps used to cool the reactor cores until the proper cooling system is restored.
"Any cutoff of the cooling mechanism is an extremely dangerous development," TEPCO official Junichi Matsumoto acknowledged.
That situation occurred Monday, after a magnitude-7.0 aftershock struck at 5:16 p.m. A tsunami warning was issued, prompting the 300 or so workers at the Fukushima No. 1 plant to evacuate to higher ground.
The evacuation order suspended work to remove highly contaminated water from a trench extending from the No. 2 reactor as well as the injection of nitrogen into the No. 1 reactor core to prevent a hydrogen explosion.
The aftershock also temporarily cut off outside power sources, which halted operations to pump cooling water into the most vulnerable No. 1 to No. 3 reactors.
The Fukushima No. 1 plant had been receiving outside power from Tohoku Electric Power Co. through three different transmission lines. Two lines that supplied power to the No. 3 to No. 6 reactors were not damaged, but the third line for the No. 1 and No. 2 reactors stopped providing electricity from the Tohoku Electric substation.
The water-pumping mechanism for the reactor cores was down for about 50 minutes before power was restored from the substation around 6 p.m.
If the outside power source could not be restored, plans called for connecting generator cars to provide electricity to the pumps. If that source was also inoperable, TEPCO workers would have had to resort to using pumps from firefighting vehicles to cool the reactor cores, much like what was done soon after the March 11 Great East Japan Earthquake.
The problem Monday was that the generator cars and firefighting vehicles had been parked near the ocean so that they could be used at anytime. But the tsunami warning prevented workers from approaching those vehicles.
Sources said TEPCO workers were likely focused on restoring the outside power source, which may have lessened their awareness of the availability of the generator and firefighting vehicles.
TEPCO sources said the generator cars would be moved to higher ground so that they could be used immediately if the outside power source was lost again.
Aftershocks continued Tuesday, further delaying work to remove contaminated water from the trench at the No. 2 reactor. A plan to collect water samples from the storage pool containing spent fuel rods at the No. 4 reactor was also delayed until Tuesday.
A TEPCO source said it would take several months to achieve a cold shutdown of all three reactors at the Fukushima No. 1 plant. The cold shutdown stage is reached when core temperatures are kept under 100 degrees.
"While we are making every effort to bring the situation under control, we are not at a stage where we can present a time frame," Matsumoto said.
The aftershocks have also led to additional work in the removal of contaminated water from the turbine buildings next to the reactor buildings.
Officials of the Nuclear and Industrial Safety Agency asked TEPCO to confirm that the condensers in the turbine buildings being considered as the location to store the contaminated water can withstand aftershocks even when full of water.
(This article was written by Masanobu Higashiyama and Hidenori Tsuboya.)