While the Columbia Generating Station’s reactor was shut down for refueling, operators inadvertently drained water from it three times. And although conditions at the plant did not threaten public safety, the mistakes have drawn a special inspection from the Nuclear Regulatory Commission.Columbia’s GE-5 boiling water reactor, located in central Washington state and operated by Energy Northwest, shut down for the outage in early April. Water must be added to the reactor pressure vessel as fuel is removed during refueling, and the NRC said in a release that it is conducting the inspection because of errant valve positions and instrumentation problems during water level changes.Quoting Energy Northwest officials, the Tri-City Herald reported that on two occasions when operators changed the water levels, valves were open at the wrong time, resulting in a total of 4,000 gallons collecting in a containment building sump. In one instance, the resulting RPV conditions also caused instruments to misread water levels.In the third incident, the paper reported, an operator error involving a missed step in a sequence of valve openings and closures earlier this month caused the water level above the fuel to drop by about an inch.The NRC reported it will also investigate two other problems that “involved temporary loss of shutdown cooling due to an electrical malfunction and the unexpected insertion of a control rod into the reactor core during a scheduled test.”Said NRC Region IV Administrator Elmo E. Collins in the release: “All of these events had very low risk significance because the reactor was in a safe shut-down condition ... But they all appear to have involved poor operator controls and warrant close examination.”
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