TOKYO (Reuters) – An accident at a Japanese nuclear research facility in June that exposed five workers to radiation has been initially deemed a Level 2 ‘incident’ on an international scale for radiological releases, the Nuclear Regulation Authority said on Wednesday.

Japan’s nuclear industry is already under public scrutiny after the March 2011 Fukushima Dai-ichi disaster. During that event, three reactors at the nuclear power plant melted down after an earthquake and tsunami. That incident was classified as Level 7, or ‘major accident,’ on the International Nuclear and Radiological Event Scale (INES), the highest rating.

The June incident occurred at a facility operated by the Japan Atomic Energy Agency in east Japan after a bag with the material burst during a check on radioactive storage inside a “controlled” room at the facility, with no radioactive material leaking outside.

Based on the amounts of exposure of the five workers, the NRA preliminarily classified the incident as level 2 on the INES scale.

One worker inhaled plutonium during the incident and as that material decays it will release between 100 and 200 millisieverts of radiation into the worker’s body over the next 50 years, National Institutes for Quantum and Radiological Science and Technology said on July 10.

That amount could increase the worker’s chances of developing cancer by 0.5 percent, the Institute said.