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Shika-1 Uncontrolled Criticality Incident Cover-up

As stated in another article in this edition of NIT, power companies besides TEPCO are due to release details of their reviews into past malpractices on March 31st. However, already more examples of past cover-ups are beginning to dribble out. Revelations of TEPCO's failure to report scrams forced other power companies to acknowledge similar cases. The most spectacular involved an uncontrolled criticality incident at Hokuriku Electric's Shika-1 (BWR, 540 MW).

The incident occurred on 18 June 1999 during a periodic inspection, which continued from April 29th to July 23rd. Preparations were being made to test the reactor's shutdown function. All control rods were supposed to have been fully inserted at the time, but three rods dropped out of position. Hokuriku Electric presumes that an incorrect valve adjustment caused the rods to drop. The reactor went critical and remained in that state for fifteen mintutes. The heads of both the reactor pressure vessel and the containment vessel were removed at the time.

The manager of the Shika plant decided not to report the incident to the government and records of the incident were not kept. The Nuclear and Industrial Safety Agency (NISA) has described the incident as "truly deplorable". It is reported that NISA suspects Hokuriku Electric may have violated nuclear-related laws, which mandate that reports be submitted about certain types of reactor incidents.

On the same day that NISA received Hokuriku Electric's confession, it ordered that the reactor be shut down, that a detailed report be submitted and that preventative measures be taken. However, this is like closing the gate after the horse has bolted. Hokuriku Electric's cavalier disregard for safety and its disdain for the regulatory system warrant a stiffer penalty. Clearly Hokuriku Electric is not fit to operate nuclear reactors, so the most appropriate response is to revoke its license.

It is worth remembering that in March last year the Kanazawa District Court concluded that Hokuriku Electric's other reactor, Shika-2, should be shut down for earthquake safety reasons (NIT 112). The wisdom of that verdict has been confirmed by this latest incident. Unfortunately, the company defied the verdict, vowing to continue operating the reactor pending the result of an appeal. (It is now shut down for other reasons - see NIT 113, 115.)

Philip White (NIT Editor)

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