Efforts are under way to stabilize overheated nuclear fuel rods and keep water temperatures in reactors in check but new challenges have emerged such as dealing with a large volume of contaminated water found inside the No. 4 reactor building. Rubble containing radioactive materials and a series of aftershocks following the March 11 massive earthquake have also been hampering work.
The road map lists three areas that need to be tackled immediately—bringing the reactors and spent fuel pools to a stable cooling condition, mitigating the releases of water and air containing radioactive materials from the power station, and monitoring radiation levels in areas around the power station.
Of the three, mitigation of radioactive releases is essential for containing an adverse environmental impact in areas around the plant as well as making it safe for workers to engage in other operations.
Priority has been placed on the handling of highly contaminated water around the turbine building of the No. 2 reactor. On April 19, work was initiated to pump contaminated water to the radioactive waste treatment facilities, to reduce the risk of it being released to the sea through a trench.
The plan calls for the work to be completed around Tuesday. As of Monday, however, no major falls had been observed in contaminated water levels around the No. 2 reactor.
At the No. 2 reactor building, a large volume of water has also been pumped into the reactor and other areas for cooling. This operation could be a factor preventing water levels from dropping. But TEPCO says that at this moment even if that is the case, nothing can be done about the situation.
TEPCO, however, is planning to increase the number of pumps to eject water. If the stalled situation is protracted, another arrangement may have to be worked out.
Another body of contaminated water, roughly five meters deep, has also been spotted in the basement of the No. 4 reactor building. The Nuclear and Industrial Safety Agency of the Ministry of Economy, Trade and Industry suspects seawater may have been left behind by the quake-triggered tsunami or an inflow of water from the No. 3 unit.
How exactly water has pooled there remains a mystery and the water could disrupt work in the days ahead. Full-fledged work has yet to be started to handle this issue.
Whether these mitigation efforts will be successful is closely linked to the cool-down operation.
Professor Hironobu Unezaki of Kyoto University Research Reactor Institute says that in order to restore cooling systems, ‘‘it is necessary to grasp how badly they are damaged and to confirm if electrical and other systems are operating.’’ Since these systems are located in the turbine building, removing the contaminated water, which hinders work, is important.
Scattered debris after explosions at the power station also pose hurdles for implementing cooling work. A high level of radiation—900 millisieverts per hour—was detected from a piece of concrete found near the No. 3 reactor building. TEPCO, which is removing debris with remote-controlled heavy machinery, says it will not pose a major impediment in implementing the road map.
It also remains to be seen if any full-fledged work can be conducted inside reactor buildings. Photos and videos taken by a pair of robots have provided glimpses of what it is like inside those buildings. Images showed damaged pieces of equipment scattered on the floor.
At the No. 2 reactor building, even robots could not obtain sufficient data as they were blocked by rubble and troubled by high temperatures and humidity. Radiation levels also remain high at many locations, which will make it all the more difficult for workers to proceed.
The road map aims to achieve conditions where radiation levels are in steady decline in the first of the three steps. Step 1 is scheduled for completion in around three months.
But at the spent fuel pool of the No. 4 reactor building, concern grew about fuel rods possibly being exposed as a result of an increase in temperatures. Water continued to be pumped in there and the situation remains changeable.
On top of these challenges, aftershocks have repeatedly suspended operations at the power station. Also feared is their impact on reactor buildings and piping badly damaged by hydrogen explosions after the first quake.
At a news conference on Monday, Goshi Hosono, Prime Minister Naoto Kan’s special adviser, admitted the risks aftershocks may impose for operations. Since the road map was presented even before the full picture of the accident at the plant becomes known, there remains the possibility of more ‘‘beyond-assumption’’ developments occurring.