Nuclear exposure toll hits 30 in J-PARC lab accident
An additional 24 researchers were exposed to an exotic soup of radioactive isotopes at the Hadron Experimental Facility in Tokai, Ibaraki Prefecture, last week, raising the tally to 30, the state-run Japan Atomic Energy Agency said late Sunday.
According to medical tests run on the 55 people involved in the troubled experiment Thursday at JAEA’s Japan Proton Accelerator Research Complex (J-PARC), at least 19 escaped exposure, the agency said. Six others are waiting to be examined.
The radioactive substances reportedly included sodium, iodine and more exotic elements.
The highest dose delivered was 1.7 millisieverts. Japan’s annual limit for nuclear workers is 50 millisieverts.
The accident occurred around noon Thursday, but the JAEA didn’t report it to the nuclear regulatory authorities until Friday night.
The JAEA said Saturday it initially thought the leak was minor and had been confined to the laboratory when the alarm went off. Workers then switched on the ventilation system, sending the radioactive contaminants outside the building.
The experiment conducted by the High Energy Accelerator Research Organization was intended to generate elementary particles by zapping a gold-covered object with a proton beam. Officials at the group said they suspect one of the electromagnets used to control the protons malfunctioned, allowing an excessively strong beam to melt the gold and release the exotic particles.
May 25, 2013
Accident of J-PARC Hadron Experimental Facility
Date & time: 11:55 May 23, 2013
Place: Hadron Experimental Facility
In the Hadron Experimental Facility experiments were conducted with the elementary particles that had been generated by irradiating gold target with proton beams. The proton beam were extracted from the main ring (MR) within much shorter time than the normal operation due to the malfunction of the beam extraction system and the gold target was bombarded with very short pulsed beam. As a result, it was suspected that the beam spot of the gold target had been heated up spontaneously and the part of the gold target had sublimed. Radioactive materials that had been generated with proton beam irradiation leaked from proton beam equipment to the experimental hall and the experimenters in the hall were exposed to the radiation. The number of personnel who entered radiation controlled area and got close to the equipment was 55.
The Hadron Experimental Facility is now shut down.
The contamination in the Hadron Hall is roughly 30 Bq/cm2.
The Hadron Hall has been shut out and the entry to the hall has been prohibited.
The measurements of radiation exposure are being carried out for the experimenters and the maximal exposure was 1.7 mSv so far.
The radiation monitors around the Hadron Hall showed slight increase, but monitoring posts at the site boundary did not show any meaningful increase. One of the two monitoring posts in the neighboring laboratory observed the temporary increase of 6 nGy/h, where normal indication is 70 to 130 nGy/h. The amount of emission of the radioactive materials to the environment is being surveyed.
Leader, Public Relations Section, J-PARC Center, Japan