From the article:
In the turbine building of the No. 6 reactor, for example, contaminated groundwater has seeped in and accumulated to a depth of up to 2 meters. If water flows into a reactor building, the emergency power system to cool the reactor may stop operating. Pumping started on May 1, and 1,700 tons of water were transferred to a makeshift tank and other facilities by Tuesday. To store water contaminated with low-level radioactive materials, TEPCO must build tanks to store about 16,000 tons of water for the coming month alone.
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– Poor estimates force timetable revision (The Yomiuri Shimbun, May. 19, 2011):
Having failed to accurately grasp the extent of actual damage to nuclear reactors and the amount of water contaminated with radioactive substances, Tokyo Electric Power Co. has been forced to revise its timetable for resolving the nuclear crisis at its Fukushima No. 1 nuclear power plant.
The plant operator released Tuesday an updated version of its road map to end the crisis, making some changes to critical aspects of the plan, especially in regards to cooling the reactors. It has been more than two months since the crisis began following the March 11 earthquake and tsunami.
TEPCO had to review its strategy on cooling the reactors as it learned about an apparent leakage of a huge amount of contaminated water from a damaged containment vessel.
The company said an estimated 87,500 tons of contaminated water has accumulated in the turbine buildings of the Nos. 1 to 4 reactors and elsewhere at the site. On Saturday, about 3,000 tons of contaminated water, which likely leaked from the containment vessel of the No. 1 reactor, was discovered in underground areas of the reactor building. Water had been pumped in to attempt to fill the containment vessel of the reactor and cool the fuel inside.
The transfer of contaminated water began Tuesday at the No. 3 reactor, following transfer operations earlier at the No. 2 reactor. But the amount of water being transferred is not keeping pace with the amount of contaminated water accumulating.
Hidehiko Nishiyama, a spokesman of the Economy, Trade and Industry Ministry’s Nuclear and Industrial Safety Agency, referred to this new problem as the amount of water pumped into the vessel must increase. “The amount of contaminated water will increase as a result [of the operation], which really is problematic,” he said on the same day.
Kenzo Miya, professor emeritus at the University of Tokyo and specialist in nuclear engineering, said, “To cool the reactor core while containing the spread of contaminated water, there will be only one option–to install a coolant circulation system, as TEPCO has decided to do.”
“With this method, it cannot rapidly cool water heated in the reactor. But under the current situation, there is no other choice,” Miya added.
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Groundwater shields planned
Measures to deal with groundwater contamination were newly included in the latest road map.
The large amount of groundwater at the Fukushima plant had been released into the sea from ditches so that it would not weaken the strength of the reactor building or flow into reactor buildings. Due to radioactive materials released in the wake of the nuclear accident, however, this underground water has been contaminated and it has not been possible to drain it as before.
In the turbine building of the No. 6 reactor, for example, contaminated groundwater has seeped in and accumulated to a depth of up to 2 meters. If water flows into a reactor building, the emergency power system to cool the reactor may stop operating. Pumping started on May 1, and 1,700 tons of water were transferred to a makeshift tank and other facilities by Tuesday. To store water contaminated with low-level radioactive materials, TEPCO must build tanks to store about 16,000 tons of water for the coming month alone.
There is a chance that highly contaminated water generated after water injection into the Nos. 1 and 3 reactors may seep into the surrounding environment, further contaminating groundwater. The new road map includes a plan to place 30-meter-high barriers in the ground around reactor and turbine buildings to block leaking water.
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500-meter dike to be built
The revised road map also includes new measures aimed at preparing for aftershocks and tsunami.
It is feared that a magnitude-8 level aftershock may follow the series of aftershocks that already have occurred since the March 11 quake.
By mid-April, an emergency makeshift power supply source was moved to higher ground and a firefighting vehicle was deployed as part of anti-tsunami measures. Backup cooling systems have also been installed.
Currently, preparations are being made to build a makeshift dike stretching for about 500 meters. TEPCO plans to complete the construction of the structure by the end of June. It will be built using stone-filled, basket-shaped containers, measuring one meter to two meters in height, that will be stacked to form a barrier 10 meters high between the coast and the Nos. 3 and 4 reactors, which were severely damaged by the Great East Japan Earthquake.
TEPCO also plans to reinforce reactor buildings and other facilities damaged by the disaster. Construction to install a concrete structure in the bottom of the No. 4 reactor’s pool to temporarily store spent nuclear fuel likely will start from Monday.
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Better facilities for workers
At the strong request of the Prime Minister’s Office, TEPCO included measures to improve the working environment for workers at the plant.
Giving consideration to the workers’ health in summer, when working conditions are expected to worsen, the measures are aimed at improving accommodation and resting facilities for them.
TEPCO plans to build a makeshift dormitory of 1,600 rooms at J-Village, a soccer training facility currently being used as a base for those workers. The new facility is expected to be made available for use as soon as July. The number of rest areas in the power plant will be increased to 10 from the current three. Better meals have also begun to be provided to the workers.
Thirty workers have had external exposure to 100 millisieverts of radiation or more. To reduce radiation exposure that workers might face in prolonged operations, TEPCO plans to cover pipes and hoses, through which highly contaminated water will flow, with lead mats. It also plans to provide workers with protective suits that are more effective at blocking radiation than those currently used.