Ibaraki nuclear research facility under scrutiny after accident; gas suspected in rupture

OARAI, Ibaraki -- A nuclear research facility here has come under scrutiny after workers were exposed to radiation while checking radioactive materials that had remained in storage for 26 years.

One of the workers exposed to radiation in the accident at the Oarai Research & Development Center of the Japan Atomic Energy Agency (JAEA) on June 6, identified as a male in his 50s, was found with up to 22,000 becquerels of plutonium-239 in his lungs, raising fears he could develop cancer or suffer other health problems.

According to the JAEA, the total level of radioactive materials that entered the man's blood, bones, organs and other parts of his body was estimated at 360,000 becquerels, based on the amount detected in his lungs.

Problems with safety management at the agency had already been pointed out, and focus is likely to turn toward whether the work at the time of the accident was appropriate.

The agency said that when the worker opened the bolted lid of a steel container during a check, the plastic bag inside ruptured, scattering dust containing uranium and plutonium. Two other workers were next to the worker at the time, assisting in the check.

The some 300 grams of dust was produced when fuel was created for the onsite Joyo experimental fast reactor, which first reached criticality in 1977. It had been placed in a polyethylene container, enclosed in two plastic bags, and then placed in a steel container, where it had been stored since 1991. There were no records to show that the container had been opened before, officials said.

The latest check was being conducted after the Nuclear Regulation Authority had pointed out problems with the management of fuel at another JAEA facility. The JAEA had planned to check 21 steel containers containing uranium and plutonium dust. The accident on June 6 occurred during a check of the first of these containers.

Why did the plastic bag rupture? Kazuya Idemitsu, a professor in the Laboratory of Energy Materials Science at Kyushu University, commented, "Over time, the atomic nuclei of uranium, plutonium and other such substances break down, releasing helium nuclei (alpha rays). When stored over a long time, helium gas would build up, and it's possible that the pressure inside the container rose, resulting in the rupture."

Sources close to the JAEA also acknowledged this possibility, with one commenting, "It may not have been a good idea to use a polyethylene container, which had a possibility of rupturing, for storage over a long period."

On June 7, the Ibaraki prefectural and Oarai municipal governments conducted an on-site inspection of the Oarai Research & Development Center under a nuclear safety agreement. Seventeen officials viewed the inside of the analysis room where the accident occurred through a monitor, and examined the concentration of radioactive materials in expelled air.

Masaaki Kondo, a safety coordinator at the prefectural nuclear power safety division, commented, "We confirmed that the damage did not spread." The Mito Labor Standards Inspection Office and prefectural police are investigating the cause of the accident and whether the work that led to it was appropriate.