Floodwaters recede at Cooper

15 July 2011

With water levels dropping in the swollen Missouri River, the emergency alert at the Cooper nuclear power plant has now been removed. However, an alert remains in place at the Fort Calhoun plant further upstream.


Cooper flooding (NPPD)
Water levels in the Missouri River have started dropping at Cooper (Image: NPPD)


Nebraska Public Power District (NPPD) declared a 'notice of unusual event' on 19 June at its Cooper nuclear power plant when the Missouri River's water level reached 899 feet (274 metres) above sea level. Storms had inundated the wider area causing the Missouri River to rise - with this being exacerbated by melting snow as well as emergency releases of water from upstream dams.


The notification - the least-serious of four emergency classifications that are standard in the US nuclear industry - was made as part of the safety and emergency preparedness plan that the plant follows when flooding conditions are in effect. The plant has continued to operate safely, but NPPD said that if the level of the river had risen to 902 feet (275 metres) above sea level, the Cooper plant - comprising a single 830 MWe boiling water reactor - would have been shut down as a "protective safety measure."


However, the company has now reported that water levels in the river near the plant have dropped to 895.8 feet (273 metres) above sea level and are forecast to continue to slowly fall. The company announced that it had therefore taken the decision on 12 July to exit the Cooper plant from the 'notice of unusual event'. Most of the flood barricades will remain in place at the plant, the company said, while selected others will be removed to all access in and around the plant.


Art Zaremba, NPPD’s director of nuclear safety assurance, commented: "Should conditions change and river levels increase, plant personnel are prepared - as we always are - to respond appropriately."


Fort Calhoun still on alert


Fort Calhoun flooding (OPPD)
Flooding at Fort Calhoun (Image: OPPD)
Meanwhile, a 'notice of unusual event' remains in place at Omaha Public Power District's (OPPD's) Fort Calhoun plant, also in Nebraska. The single 482 MWe pressurized water reactor at Fort Calhoun has been in safe shutdown since 9 April, when it entered a scheduled refuelling outage.


OPPD declared a 'notice of unusual event' at the plant on 6 June when flood waters reached 1004 feet (306 metres) above mean sea level. By the end of June, water levels stood at 1006 feet.


Fort Calhoun was designed for floods up to 1014 feet (309 metres) above sea level. Berms and temporary AquaDams have been installed around Fort Calhoun's main plant buildings as well as the electrical switchyard and administration area. The official flooding alert will remain in effect at Fort Calhoun until OPPD can be sure the level of the river would remain below 1004 feet.


Staff from the US regulator, the Nuclear Regulatory Commission, will meet with OPPD officials on 27 July to discuss the status of actions being taken to keep the plant safe during flooding at the site and planned post-flooding recovery actions.


Researched and written

by World Nuclear News