Extra Nuclear Regulatory Commission staff members are once again on-site at the Fort Calhoun nuclear plant to review a report that recently installed water pumps were improperly bolted down.In a release Monday, the NRC said it is investigating a condition reported in early December involving four raw water pumps secured with bolts that were too short to meet seismic requirements. The agency is also reviewing a checklist of other items the Omaha Public Power District plant must address before it can restart.The single-unit plant shut down in April of 2011 because of flooding on the Missouri River. It received an NRC red finding after a fire in a switchgear room two months later temporarily cut power to spent fuel cooling systems. Exelon has been hired to take over day-to-day management of the plant, and a special NRC panel has placed it under enhanced regulatory scrutiny. Late last year the agency required that Fort Calhoun enhance flood barriers, emergency diesels and containment maintenance, which pushed OPPD's restart target date into the first quarter of this year.