During recent maintenance work at the Ikata nuclear power plant that was to include the country’s first removal of spent mixed-oxide (MOX) fuel following full-scale ‘pluthermal’ power generation, a control rod was removed from the reactor by mistake, according to Shikoku Electric Power Co. The incident involving reactor No. 3 at the plant in Ikata, Ehime Prefecture, caused no loss of control of the nuclear reaction in the unit and no radioactive materials were released, the company said recently. The reactor has been shut down since Dec. 26 to perform the maintenance work.
Control rods are used to suppress nuclear fission, and are inserted in order to halt a nuclear reactor. According to the power company, for fission to be allowed to occur within the reactor, it is necessary to adjust the concentration of boron within the reactor coolant in addition to removing the control rods.
The company had planned to start removing the spent MOX fuel assemblies, which contain a blend of plutonium extracted from spent nuclear fuel and uranium, from the reactor at 12 a.m. The work is now expected to be delayed due to the company’s investigation into the incident involving the control rod.