Over the past several weeks, workers at Japan's crippled Fukushima Daiichi nuclear power plant have started the first big task in the 40-year process of decommissioning the plant. On the top floor of reactor building 4, workers have begun removing the 1533 fuel assemblies from the spent fuel pool. The operation is expected to be completed by the end of 2014.
During the crisis at the plant in March 2011, a tsunami knocked out power and triggered meltdowns in reactors 1, 2, and 3. Reactor 4 was shut down for maintenance and refueling at the time of the accident, which meant that all of its fuel rods were stored in the building's spent fuel pool. When an explosion rocked the reactor 4 building on March 15 , experts worried that the blast had damaged the pool and that water was leaking out, leaving the nuclear fuel exposed to the air. Since the spent fuel pools aren't shielded by heavy concrete or steel structures, such exposure would release a great deal of radiation into the environment.
While it was eventually determined that the reactor 4 pool did not lose water, experts continued to worry that the pool was no longer structurally sound. TEPCO, the utility that owns the Fukushima Daiichi plant, therefore reinforced the building, and made it a priority to empty that pool.
The process, shown in the video below, involves first lowering a cask into the pool. Then the fuel assemblies are lifted one at a time and placed in the submerged cask. These transport casks, which contain shielding to block the nuclear fuel's radiation, are then lowered to a truck and brought to a common pool in a more secure and intact building.
TEPCO has completed two rounds of this operation, bringing a total of 44 assemblies to the common pool. They have 68 more trips to go.