MITO, Ibaraki Pref. — Police on Wednesday raided the headquarters of JCO Co. in Tokyo and its nuclear fuel processing plant in Tokai, Ibaraki Prefecture, as the repercussions of last week’s nuclear accident continued to reverberate throughout the country.

According to the search warrant, police are investigating the plant on suspicion of professional negligence and for evidence that the unit of Sumitomo Metal Mining Co. violated nuclear power plant regulations when its workers mixed the enriched uranium fuel.

It was the first raid on a firm suspected of professional negligence leading to a nuclear accident.

Police limited their search at the plant to an office building and other locations, due to safety considerations. The fuel conversion building, where the accident occurred, is apparently still dangerous.

Investigators are already alleging that JCO altered its processing manual without authorization from authorities and was negligent in teaching employees about the hazards of working with uranium.

Three JCO workers last Thursday morning reportedly used steel buckets to transfer a large amount of a powdered uranium compound into a vat of liquid nitric acid, setting off an uncontrolled fission reaction that nearly killed them and exposed 49 people, including local residents, to radiation.

The Science and Technology Agency the same day decided to revoke JCO’s business license after confirming that the Tokai, Ibaraki Prefecture, processing plant bypassed government procedures.

The action — the heaviest administrative penalty that can be taken — will be the nation’s first revocation of a nuclear plant’s business license. The measure will take place after radioactive substances are removed from the facility and the plant has been safely secured, agency sources said.

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