Workers exposed to radioactive materials at a Japan Atomic Energy Agency (JAEA) facility in Ibaraki Prefecture ignored a safety checklist item on whether the containers "could be ruptured," the agency revealed on June 15.
Five workers at the JAEA's Oarai Research & Development Center in Oarai, Ibaraki Prefecture, were exposed to uranium oxide and plutonium oxide powder when the bags holding the materials burst open during a June 6 inspection. The materials were kept in a polyethylene container double-wrapped in plastic bags, all in a stainless steel vessel.
According to the JAEA, the "regular safety checklist" was put together soon before the accident and listed 30 items for inspecting radioactive materials held at its nuclear R&D centers. One of those items called on workers to determine if there was a risk of fire, or were fears of "an explosion, a rupture, or scattering" of the powdered materials.
However, the workers at the Oarai facility apparently decided that the checks regarding the risk of "rupture" were "not applicable" because the materials had been double-wrapped in plastic bags, and they only checked the containers' exteriors.
The agency on June 15 also released footage of the radioactive materials container taken by one of the workers just after the accident. The image shows the plastic bags protruding from the top of the stainless steel vessel. The JAEA is scheduled to submit an accident report to the Nuclear Regulation Authority on June 19.
The accident occurred when one of the workers unsealed the stainless steel outer vessel, which had not been opened for 26 years. A JAEA spokesperson told reporters at a June 15 news conference that the workers' failure to consider the risk of rupture was "inappropriate."