Officials from local municipalities and the Ibaraki prefectural government inspected a nuclear physics laboratory in Ibaraki Prefecture on May 25 where thirty scientists are confirmed to have inhaled radioactive materials as a result of a May 23 accident that was not reported to the public for more than 30 hours.
The representatives of the Ibaraki prefectural government and seven surrounding municipalities inspected the Japan Proton Accelerator Research Complex (J-PARC) in the village of Tokai in the afternoon on May 25. In the on-site inspection, an official with the Japan Atomic Energy Agency (JAXA), operator of the facility, said that the leakage of radioactive materials was an unanticipated accident.
As for the delay in reporting the accident to local governments, an official of the prefectural government asked, “Was it not possible to report it to us more quickly?”
Satoru Kondo, director of JAXA’s Nuclear Science Research Institute, apologized for the delay.
“We are very sorry," he said. "The accident occurred as an unexpected malfunction of a machine.”
The inspection confirmed the location of the device that was involved in the accident, and those of scientists who had been exposed to radiation from inhaling radioactive materials in their bodies. JAXA confirmed the initial number of four scientists having been exposed had risen to thirty as of May 26.
Kondo also admitted that the facility has not taken safety measures, such as installing filters on ventilators, to prevent radioactive materials from leaking outside.
Taichi Miura, head of the safety division at J-PARC, said, “As for the fact that we released (radioactive materials out of the facility), our way of thinking about and dealing with the possibility was too lax.”
In the accident that occurred at around 11:55 a.m. on May 23 in the Hadron Experimental Facility, gold, which was being bombarded by proton beams to generate elementary particles, evaporated as the intensity of the beams rose to 400 times normal levels, possibly as the result of a glitch in the power supply system. As a result of the evaporation, radioactive materials were released.
At the time of the accident, 55 people were near the device that caused it. The JAEA completed health checks on 49 of them by the evening of May 26. Using whole body counters, it checked whether they were exposed to radiation by inhaling the radioactive materials.
As a result, 26 more scientists--24 men and 2 women--were found to have suffered internal exposure. Earlier, the other four scientists, all male, were reported to have received internal doses of up to 1.6 millisieverts, about equal to the level of the annual background dose of people living in Japan.
Keiji Miyazaki, professor emeritus of nuclear reactor engineering at Osaka University, said, “Evaporation of materials that are being hit by beams could also take place in accelerators in other parts of Japan. Verification should be conducted to see whether J-PARC was complying with safety regulations.”
Accelerators, like the one in J-PARC, are in operation in various parts of Japan. However, safety standards on them are looser than those on nuclear reactors.
Accelerators increase the speed of particles, such as electrons and protons, to near the speed of light and, as a result, produce intense beams. These beams are then used to strike and collide with other substances.
According to the Particle Accelerator Society of Japan, accelerators were operated in 38 facilities in Japan as of the end of 2012. They are used for a growing number of purposes, such as for studies on elemental particles, development of new materials or medicines and studies on cancer treatments.
J-PARC was jointly set up by JAXA and the High Energy Accelerator Research Organization (KEK) in 2008. JAXA is in charge of experiments for industry use, such as structural analysis of proteins and development of batteries. KEK mainly conducts studies on basic science, such as experiments on elemental particles.
J-PARC has several accelerators. Of these, the largest has a circular shape, with a diameter of about 1.6 kilometers.
One of the experiments being conducted with the accelerator is to send a particle, called a neutrino, to Super-Kamiokande, a neutrino observatory constructed in the remains of the Kamioka zinc mine in Gifu Prefecture, which is 295 kilometers from J-PARC. The Tokai to Kamioka (T2K) experiment is being implemented to see the nature of a neutrino.
The May 23 accident occurred in an experiment that was being conducted under the initiative of the KEK.
Measures to secure the safety of accelerators are stipulated under the radiation hazard prevention law. Even in conventional operations of accelerators, cooling water around the devices changes to radioactive materials if beams hit the water. Therefore, scientists are obliged to measure radiation levels and check waste disposal.
Compared with nuclear reactors, however, accelerators use less amounts of radioactive materials. Therefore, areas where radiation levels must be controlled are not widespread.
As accelerators can be halted immediately, they are regarded as equipment whose level of danger is generally low, said a science ministry official. Because of that, the accelerators are not subject to safety checks or guidelines that are applied to nuclear reactors under the law on the regulation of nuclear reactors and other equipment.
Usually, decisions on what accident prevention measures are needed are left to accelerator operators, except for measuring radiation levels and holding regular briefings for those dealing with radiation.
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