The five workers exposed to airborne plutonium at Japan’s Oarai Research & Development Centre in Ibaraki Prefecture were quarantined for about three hours in the room where the accident occurred, a Japan Atomic Energy Agency official said on 9 June. The action was taken to prevent the plutonium and other radioactive contaminants from spreading to other parts of the facility, but it increased their internal exposure, Kyodo news reported. Internal radiation exposure has been confirmed in four of the five men.
Education and science minister Hirokazu Matsuno told a news conference that a team in the ministry would question JAEA President Toshio Kodama about the accident, which occurred on 6 June when a worker opened a sealed metal container holding plutonium and uranium powder samples. A plastic bag containing the samples inside suddenly ruptured, spreading the radioactive materials. Subsequent lung checks showed that the man had 22,000Bq worth of plutonium-239 in his system, compared with 5600 to 14,000 becquerels in three of the other four personnel.
JAEA said the floor of the room is giving off 55Bq of radiation per square centimetre in the area in front of the apparatus in which the container was placed before it was opened. The acceptable level is 4Bq, according to the Nuclear Regulation Authority (NRA). The metal container had not been opened once since it was sealed in 1991, and was being checked on the instructions of the NRA.