Police suspect that the workers were instructed by crew leaders and possibly executives to violate procedures in handling the dangerous material in the interest of efficiency. The production of fuel was intended for an experiment with a fast-breeder reactor, a controversial type of plutonium reactor. This explosion was the second related to fuel production for fast-breeder reactors. The first took place in 1997 at another plant in Tokaimura. That accident resulted in an explosion and fire which exposed 35 employees to high levels of radiation.
Japan has a strong economic interest in utilizing fast-breeder reactors.
Uranium converts from non-fissile material to an isotope of plutonium. Steenwyk also pointed out that when too much material, such as uranium, is put into a small space, it constitutes critical mass, which causes a nuclear chain reaction and an explosion. Because of the desirability of the fast-breeder nuclear reactors for providing the Japanese with their own source of energy, they may continue their nuclear energy production despite the costs.