The Nuclear Regulatory Commission (NRC) released its annual report on abnormal occurrences for 2011, citing 23 events involving radioactive materials and one event at a commercial nuclear power plant.
An accident or event is considered an abnormal occurrence if it involves a major reduction in the degree of protection of public health and safety. According to the NRC, abnormal occurrences can include, but are not limited to, moderate exposure to or release of radioactive material licensed by the NRC or a state agency; major degradation of safety-related equipment; or major deficiencies in design, construction, use of or management controls for facilities or radioactive material at NRC-licensed facilities.
For 2011, there was one abnormal occurrence at an NRC-licensed nuclear power reactor. This occurred on Oct. 23, 2010, at Unit 1 of the 3,300 MW Browns Ferry Nuclear Plant, with the failure of a low-pressure coolant injection flow control valve, part of the reactor’s residual heat removal system. Although no event occurred and the public was never in danger, the NRC determined that the valve failure caused a weakness in the licensee’s fire mitigation strategy, increasing the likelihood of core damage in event of a major fire. The determination resulted in a red finding under the NRC’s Reactor Oversight Process, for a finding of high safety significance.
Three other events that did not meet the criteria to be classified as abnormal occurrences are included in the report because of high public and media interest. These are the Japanese event at Fukushima Daiichi nuclear plant, flooding at Fort Calhoun plant in Nebraska, and the August 2011 earthquake near the North Anna plant in Virginia.
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