Offline for almost two years, a Nebraska nuclear plant was told this week that it must address additional issues before being allowed to restart, according to federal regulators.
The U.S. Nuclear Regulatory Commission issued an updated Confirmatory Action Letter (CAL) on Tuesday (Feb. 26) outlining three additional actions the Omaha Public Power District (OPPD) officials have agreed to take before restarting the Fort Calhoun nuclear plant.
The new CAL items include a requirement to address safety system functional failures, containment internal structure issues, and the use of Teflon as a sealant on electrical cables inside containment.
Photos: Omaha Public Power District
The NRC issued an updated action letter on Feb. 26 with three new requirements for restarting the Fort Calhoun Station nuclear power plant in Omaha.
The plant shut down on April 9, 2011 for a scheduled refueling outage and was nearing completion on June 3, 2011, when flooding required management to suspend outage work and restart activities to focus on flood protection.
Located 19 miles north of Omaha, it is owned and operated by OPPD.
The amount of flooding, which OPPD described as "unprecedented in the U.S. nuclear power industry," peaked at over 1,006 feet above mean sea level and stayed close to that level for more than a month. The plant was protected to 1,014 feet.
Identify and Resolve Issues
NRC previously issued a CAL in June 2012 with a list of action items, or the "Restart Checklist."
The updated CAL, addressed to OPPD's VP and Chief Nuclear Officer, Lou Cortopassi, said the purpose of the Restart Checklist was to verify that the "issues that resulted in the prolonged performance decline at Fort Calhoun Station are resolved."
NRC is requiring OPPD to identify the causes and resolve issues that led to numerous safety system functional failures (SSFF) that were identified over the course of a year. If a key system has the potential to fail, the NRC defines it as a SSFF.
One example of a SSFF at the Fort Calhoun plant was an electrical switchgear fire in June 2011 that disrupted power to vital systems and components needed for the safe shut down of the plant, the NRC said.
OPPD must identify the causes and resolve two existing conditions inside containment. Plant workers discovered that structures supporting equipment did not meet all design requirements. Also, over 600 pipes housing electrical cables that run through the containment building are insulated using a material known to degrade in some accident scenarios involving high radiation exposure.
OPPD acknowledged receipt of the revised CAL in a message on its website that said, "OPPD has been aware of all of the items in the new CAL and has been working on them for months.
"Significant progress has been made with NRC inspections well underway. The NRC inspections and the extensive work will add value to help bring Fort Calhoun back to a high performing plant."
OPPD President and CEO Gary Gates stated, "OPPD leadership and our board of directors are committed to doing everything possible to return Fort Calhoun Station to a high level of performance in a safe, efficient and timely manner."
On Jan. 8, 2013, NRC and OPPD held a public meeting to discuss progress made toward restarting the plant.
OPPD presented its status for each Restart Checklist item and stated that its flood recovery plan was 94 percent complete.
In December 2012, OPPD released a slide presentation regarding containment internal structures (CIS). The history and identification of the CIS issues at the plant was provided by Bernie Van Sant, the district's CIS Project Engineering Lead.
An aerial photograph from June 15, 2011, shows the "unprecedented" level of flooding that Fort Calhoun Station withstood for more than a month.
According to the presentation, the issue involves the concrete CIS that supports plant components and systems inside containment.
During an extended power uprate analysis, a discrepancy was discovered with the containment cooling water system pipe supports. Issues were then identified with original CIS calculations that included incorrect, incomplete or missing calculations; inconsistencies between calculations and drawings; and incomplete consideration of all load combinations.
New design options were presented by Tom Dailey, CIS Project Manager. He listed the current preferred option as cast-in-place concrete, explaining that there are fewer interferences compared to the structural steel or precast concrete options.
In the closing remarks, Bruce Rash, the Recovery Director, noted that OPPD was "committed to safe restart" and was "dedicated to support NRC inspection of CIS operability for restart."
About the Plant
Fort Calhoun Station is a 478.6-megawatt nuclear power plant located on the Missouri River. Designed and constructed at an initial cost of $178 million, the platn began producing electricity on Sept. 23, 1973.
The containment building was constructed with steel-reinforced concrete. The walls are almost four feet thick, a one-fourth-inch-thick carbon steel liner ensures leak-tightness, and the floor is more than 12 feet thick, according to OPPD.
In 1993, the NRC granted the station a license extension to 2013; in 2003, NRC again extended the license, this time by 20 years.