Tokyo Electric Power Co. on Nov. 18 started removing some 1,500 nuclear fuel assemblies from a pool atop the No. 4 reactor at its Fukushima No. 1 nuclear power plant. The work, scheduled to continue through December 2014, is the first step in decommissioning of the whole plant, expected to take 30 to 40 years. Because the removal of nuclear fuel is extremely dangerous, Tepco must do it with utmost care. It also should keep local governments and residents near the plant fully informed about the progress of the fuel removal so that they can quickly take necessary action if an accident occurs.
On March 15, 2011, in the early stages of the triple meltdown of the Nos. 1, 2 and 3 reactors at the plant triggered by the 3/11 megaquake and tsunami, the building housing the No. 4 reactor suffered a hydrogen explosion that blew its roof off. At the time, the core of the No. 4 reactor did not contain any nuclear fuel because it was undergoing a regular inspection. But in a water pool on the fifth floor of the building were stored 1,535 nuclear fuel assemblies, each 4.5 meters long — 1,331 of them containing spent nuclear fuel, which is highly radioactive. In the first part of the removal work, assemblies of fresh nuclear fuel will be removed.
Tepco should not assume that the fuel removal will go smoothly in accordance with its work schedule since it has no experience in removing nuclear fuel assemblies from a building destroyed by an explosion. It should have the wisdom and courage to slow down or temporarily stop the work if necessary. The possibility cannot be ruled out that some fuel assemblies were damaged by falling debris or may be damaged during the removal work.
The removal is extremely delicate work. A transport cask is lowered from an overhead crane into the water pool on the fifth floor and another crane is used to put fuel assemblies into the cask one by one. The cask is then lifted. After a decontamination process, the cask is loaded on to a trailer on the first floor and moved to an undamaged building about 100 meters away. There fuel assemblies will be kept in a common pool, which in the future will also store fuel assemblies from the other reactors. It takes about a week to move one cask from the pool above the reactor to the common pool. If fuel assemblies fall while being moved by the overhead crane to the ground, a serious situation could develop with radioactive substances spreading into the atmosphere.
Tepco has worked out individual scenarios to deal with stoppages of pool cooling, water leaks from the pools, a massive earthquake, a fire and an accident involving the trailer, but not for dealing with a situation in which two or more incidents occur simultaneously. Therefore it must proceed in an extremely careful manner. Because of the nature of the work, Tepco also should not neglect efforts to reduce workers’ exposure to radiation.