The operator is having difficulty pumping water into destroyed reactors at the Fukushima No. 1 plant, tanks are rapidly filling with radioactive water, and hundreds of potentially volatile uranium fuel assemblies remain in a precarious storage pool that some warn could collapse in another strong earthquake.
The operator is having difficulty pumping water into destroyed reactors at the Fukushima No. 1 plant, tanks are rapidly filling with radioactive water, and hundreds of potentially volatile uranium fuel assemblies remain in a precarious storage pool that some warn could collapse in another strong earthquake.
But Tokyo Electric Power Co. is working on solving those problems, with plans to build new storage tanks, to erect an overhead crane to lift the fuel, and to decommission the destroyed reactors within 40 years.
Cooling the reactors produces about 450 tons of radioactive water daily. Some of that water is treated and reused as coolant, but as of Sept. 4 storage tanks at the site held about 200,000 tons of contaminated water.
TEPCO plans to build more tanks to increase the overall capacity to 700,000 tons.
Meanwhile, the volume of water pumped into the pressure vessels of the No. 1, No. 2 and No. 3 reactors fell below a mandated minimum level on Aug. 30, for the first time since immediately after the 2011 earthquake and tsunami.
The reactors remain in what is known as cold shutdown. Temperatures within the outer containment vessels and at the bottom of the pressure vessels remain largely stable, between 35 and 55 degrees.
However, lumps of melted nuclear fuel likely remain piled inside the reactors, mainly in the containment vessels.
TEPCO has been adjusting injected water to keep the reactors cool, but the fuel clusters continue to generate heat and the plant operator has yet to come up with a full solution.
The company suspects that the pipes carrying water to the reactors from tanks may have been choked by chips of polyethylene, a material used in the piping.
Another problem is groundwater, which flows into the reactor buildings and becomes contaminated. TEPCO plans to dig 12 wells west of the reactor buildings and pump out water, to lower the overall level of groundwater so that it will not enter the buildings.
It has also begun preparing to decommission the reactors, which will take an estimated 30 to 40 years.
The key task will be to remove molten nuclear fuel from the three crippled reactors. Before that, the company needs to understand fully what is going on inside.
In early October, TEPCO will use a camera to examine conditions within the No. 1 reactor’s containment vessel. The company will also measure radiation levels, temperatures and levels of contaminated water.
It has already inspected conditions within the No. 2 reactor by deploying an endoscopic camera to look inside.
Thermometers will be installed inside the No. 1 reactor so temperatures can be monitored on a regular basis.
The company also plans to develop robots for work within the reactors. It hopes to use them for inspections, and to repair water leaks and remove radioactive materials.
TEPCO plans to begin removing nuclear fuel from the storage pool at the No. 4 reactor in December 2013 and move its bundles of uranium rods to a pool elsewhere at the plant.
Workers will erect a cover over the reactor building, equipped with a crane to lift fuel from the pool inside. Work on the cover's foundations is already under way.
In July, TEPCO carried out a trial in which it removed two fuel assemblies from the storage pool at the No. 4 reactor. It inspected the fuel and found no major abnormalities.
In August, the combined amount of radioactive cesium released from the No. 1, No. 2 and No. 3 reactor buildings stood at about 10 million becquerels per hour. It stayed at low levels after falling in February.