On June 6, 2011 the Omaha Public Power District, as required by Nuclear Regulatory Commission guidelines, declared a Notification of Unusual Event (minimal level on a 4 level taxonomy) due to the flooding of the Missouri River. The Missouri River is above flood stage and is expected to rise further and remain above flood stage for several weeks to a month. Contractors have been busy installing sandbags and earthen berms to protect the facility from flooding. According to officials, the plant was built to withstand a 500 year flooding event and though by June 14, 2011, much of the facility was surrounded by the swollen Missouri River, Omaha Public Power District officals were confident that enough redundancies were in place to ensure adequate safety. It was reported on June 17, 2011 that the plant was in “safe cold shutdown” mode and that four weeks worth of additional fuel had been brought in to power backup generators, should they be needed. The Army Corps of Engineers indicated that with average precipitation, the Missouri River would not go above 1,008 feet (307 m) above sea level and OPPD officials stated that the current flood protection efforts would protect the plant to 1,010–1,012 feet (310–308 m) feet above sea level. Officials indicated the spent fuel pool is at 1,038.5 feet (316.5 m) above sea level. The Federal Aviation Administration has declared a “temporary flight restriction,” in a two nautical mile radius, centered on the Fort Calhoun nuclear facility. This restriction went into effect on June 6, 2011, at 4:31 PM, and remains in effect “until further notice.”
On June 7, 2011, an electrical component in a switcher room caused a small fire with poisonous gases and Halon extinguisher activation which forced a partial evacuation. The fire was no longer active when firefighters arrived and according to officials, the public was never in any danger, however in response, the Omaha Public Power District declared an Alert (second level on a 4 level taxonomy). The fire impacted a pump which is used to recirculate coolant water through the spent fuel pool. The pump was offline for an hour but backup equipment was not needed as the estimated time for the pool to reach boiling temperature was over 88 hours. The evacuation was the first at the facility since 1992, when 20,000 US gallons (76,000 l; 17,000 imp gal) (ca. 76 t) of coolant leaked into a containment building from the reactor
Le esondazioni del fiume Missouri in Nebraska stanno minacciando due centrali atomiche: Fort Calhoun e Cooper. Così come è avvenuto in Giappone per la centrale di Fukushima, il rischio che si corre è quello della sospensione della rete elettrica, che impedirebbe il corretto raffreddamento del nucleo. L'inondazione è stata provocata dalle abbondanti piogge cadute negli ultimi giorni sulle Grandi Pianure ma anche dalla fusione del cospicuo manto nevoso delle Montagne Rocciose. ..