Nuclear workers who inspected the area in the Fukushima 4 reactor building under the spent fuel for the first time since the M9.0 earthquake and tsunami were met by a scene of destruction. TEPCO's plans to cool the spent fuel pool using existing plumbing will have to be scrapped. The plumbing that would have been used to cool the spent fuel pool is broken, bent and twisted beyond repair. The water in the spent fuel pool is close to boiling. TEPCO has been unable to cool the spent fuel pool below a temperature NHK reports as "above 80 degrees Celsius."
Because reactor 4 was being refueled when the earthquake struck in March, the spent fuel pool contains an exceptional amount of nuclear material. All the fuel from the reactor, plus a large inventory of old spent fuel is contained in the spent fuel pool that looms above the reactor vessel at the 4th story of the building that contains the reactor. TEPCO is working hard to prevent a loss of coolant accident that could lead to a spent fuel fire or hydrogen explosion which could spread radioactivity to the environment.
On Friday, workers entered the 4th floor of the No.4 reactor building where the pool is located for the first time since the nuclear disaster took place.
They found a large hole in a wall created by the March 15th explosion. They also discovered that a nearby pipe necessary for the cooling system had been mangled.
TEPCO says the repair team found it hard to work near the pool as equipment had been destroyed and debris was scattered on the floor.
TEPCO workers installed steel supports under unit 4's spent fuel pool to prevent its collapse.
Because the spent fuel pool was designed for ease of refueling the reactor, not spent fuel storage, it is located high in the reactor building. Expert nuclear engineers have been flummoxed about how to deal with the situation at unit 4. Because the spent fuel is highly radioactive and densely packed workers cannot service the pool without risking high radiation exposure. It is hard to get heavy equipment high into the reactor building to get the spent fuel out the pool. And it is hard to keep the pool cool.
Moreover, the continued high levels of I-131, with a half life of just 8 days, near unit 4 could indicate criticality events might have taken place in the spent fuel pool since the earthquake. Because we don't know how the radioactive water got to where it is this is just a possibility. However, the ratios of Iodine-131 to Cesium-137 should be dropping rapidly because Cesium-137 has a much longer half life of 30 years. The continued high levels of Iodine-131 at several sites near units 2, 3 and 4 indicates that something is happening but we don't know what it is.
Fukushima unit 4's spent fuel looms like a radioactive sword of Damocles over Japan.
Boiling water reactors in the United States have similar spent fuel pools to Fukushima's. This incident shows that these pools are unsafe for spent fuel storage. These pools were clearly never designed for spent fuel storage. The USNRC should direct the nuclear industry in the United States to remove, as quickly as possible consistent with worker safety standards, all spent fuel from storage in pools similar to Fukushima's.