NRC to send special investigation team to Wolf Creek after extended outage

Federal inspectors will visit the Wolf Creek nuclear power plant next week to determine why an offsite power loss caused an automatic shutdown at the plant. The NRC team will work with two inspectors who are at Wolf Creek fulltime.

Additional NRC inspection follow-up is planned to assess the circumstances surrounding the event and some unexpected conditions during and following the NOUE, including a small essential service water leak inside containment, a ground alarm on emergency diesel generator B, a trip of the turbine-driven auxiliary feedwater pump after 12 hours of operation, and a failure of the temporary diesel-driven fire pump. Inspectors will also review the impact on operations of not having power to non-vital loads for a prolonged period of time.

AIT’s are used by the NRC to review more significant events or issues at NRC-licensed facilities. The six-member team has assumed responsibility from the resident inspectors for gathering information about the shutdown event and will travel to the site in the coming weeks. The team will be led by NRC Region IV Branch Chief Mark Haire of the Division of Reactor Safety.

The Wolf Creek nuclear power plant located near Burlington, Kansas, occupies 9,818 acres (40 km²) of the total 11,800 acres.  Concerns about safety system function failures and unplanned plant shutdowns at Wolf Creek in 2010 had resulted in the NRC putting the plant on its increased oversight list in early March of 2011.  This prompted Wolf Creek to undergo the most significant maintenance work since construction in 1985, including all four turbine rotors.

Of the nation’s 104 nuclear reactors, Wolf Creek’s lone reactor was one of the three to be placed on the NRC’s third level of heightened oversight list.

Wolf Creek had six safety system function failures in 2010, and three unplanned plant shutdowns. One of those was the discovery of gas accumulation in the cooling water system and residual heat removal system during the summer.
The closest nuclear power plant to tornado-ravaged Joplin, Mo., was singled out weeks before the storms of May 2011 hit,  for being vulnerable to twisters.  Specifically, plant operators and federal inspectors said Wolf Creek did not secure equipment and vehicles needed to fight fires, retrieve fuel for emergency generators and resupply water to keep nuclear fuel cool as it’s being moved.

2011 – The toughest summer on nuclear power plants in recent history

At Browns Ferry in Alabama, storms disabled sirens, meaning that police and emergency personnel would have had to use telephones and loudspeakers in a crisis.

At the Surry Power Station in Virginia, documents obtained by The Associated Press show that a tornado badly damaged a fuel tanker used to refuel a backup generator.

At the North Anna nuclear power plant workers continue to frequently find and assess damage and faulty parts after being rocked by a earthquake over design basis and Operating basis earthquake ground motion limits.

 

Those instances, along with the situation at Wolf Creek, highlight a larger problem at the nation’s 104 nuclear reactors: While reactors and safety systems are designed to withstand a worst-case earthquake, flood, or tornado, that doesn’t necessarily mean all emergency equipment or the buildings that house such equipment are disaster proof.

But the current outage at Wolf Creek doesn’t include any extreme weather or external events, instead it seems that the lights (power) ‘just went out’, and worse yet, no one knows why.  The  Plant shutdown after a main generator electrical breaker failed, followed by an unexplained loss of power to an electrical transformer. This caused the switchyard to become de-energized, which removed the plant’s connection to the electrical power grid.

In an emailed statement to Power Engineering magazine on Jan. 16, Wolf Creek spokesperson Jenny Hageman said plant operators were not speculating as to when the plant will be back online.  An investigation continues into the cause of the breaker failure and the loss of power.

Locals have reported there was “quite a steam release” with this event, but the utility said no radiation was released during the event.

Report Summary of Wolf Creek  2009 Power Outage Incident

The Near-Miss

The NRC sent an SIT to the site after a nearby lightning strike on August 19, 2009, disconnected the plant from the electrical grid. The reactor and turbine automatically shut down in response, as designed. Onsite emergency diesel generators started automatically, to provide electrical power to essential safety equipment. Essential service water (ESW) pumps also started automatically.

However, a pressure spike in the ESW system after the pumps started created a 3/8-inch-diameter hole in the piping. The SIT investigated the loss of offsite power and the ensuing damage to the ESW system (NRC 2010y). The SIT found that a 2007 internal study had forecast leakage in the ESW piping, and that leakage had actually occurred in April 2008 in an event similar to that in August 2009.

The NRC sanctioned the company for having identified this safety problem but having failed to correct it.

How the Event Unfolded

The SIT found that Wolf Creek personnel had little responsibility for the plant’s electrical switchyard. Most responsibility rested with Westar Energy, an independent electricity provider. This division of responsibility meant that workers at Wolf Creek did not enter all switchyard-related problems into the plant’s corrective action program, which determines the root causes of equipment failures and proper fixes.

For example, one or more transmission lines between the plant and the electrical grid had failed 31 times since 2004, but workers had not entered 20 percent of those failures into the corrective action program. The SIT also learned that when Wolf Creek workers received accounts of switchyard problems at other nuclear facilities, they did not effectively communicate that information to Westar Energy. The plant was therefore more vulnerable to offsite power interruptions than necessary.

The loss of offsite power triggered several fire protection alarms. Plant procedures called for workers to monitor areas triggering the alarms, to compensate for the disabling of automatic fire detection and suppression circuits owing to the loss of power. NRC inspectors discovered that more than a dozen areas lacked the required fire watches.

The plant’s response to the loss of offsite power, and the resulting rupture in the ESW piping, led to a sizable leak in the auxiliary building—discovered by an NRC inspector seven hours later. During an accident or a loss of offsite power, this plant’s ESW system draws water from a nearby lake for numerous cooling systems, including one used to remove heat from the reactor core and containment.

The SIT found that similar leakage in ESW system piping had occurred after another loss of offsite power in April 2008. The SIT concluded that the company’s evaluations after these two events were too narrow to determine the causes and consequences of the problem. Specifically, the SIT found that the company had not adequately evaluated the damage caused by internal corrosion of ESW system piping and components.

The SIT also found that a 2007 assessment of the ESW system found that lake water was causing pitting and other corrosion. The study recommended better chemistry control and monitoring measures to prevent damage. However, managers opted to delay “repairs until such degradations (pitting) had become through-wall leaks” (NRC 2010y).

NRC Sanctions

The SIT documented two violations of regulatory requirements associated with the ROP’s initiating events cornerstone. One violation involved the failure to enter electrical switchyard problems into the corrective action program.

The second violation involved failure by the operators to control the water level in the steam generator after the reactor shut down. The NRC classified both violations as Green.

The SIT identified five other violations of regulatory requirements associated with the ROP’s mitigating systems cornerstone. The first involved the failure to assess the impact of the through-wall leaks caused by internal corrosion of ESW piping on the system’s operability.

The second violation involved inadequate corrective action following damage to ESW piping after the loss of offsite power in April 2008. The third violation involved inadequate corrective action related to the corrosion problems identified by the ESW assessment in 2007.

The fourth violation involved failure to develop and implement needed procedures. Wolf Creek required operators to visually examine systems subject to water-hammer forces during electrical events for structural damage.

However, the company did not include the ESW system in such inspections, despite the fact that a water hammer after the loss of offsite power in April 2008 damaged ESW piping and components.

The fifth violation involved a violation of the plant’s operating license, reflected in the inadequate response to fire protection alarms. The NRC classified all five violations as Green.

 

NRC TO SEND AUGMENTED INSPECTION TEAM TO WOLF CREEK NUCLEAR GENERATING STATION

The Nuclear Regulatory Commission will send an Augmented Inspection Team (AIT) to the Wolf Creek Nuclear Generating Station to review the circumstances surrounding an automatic reactor trip and loss of offsite power that occurred there on Jan. 13. The plant is located near Burlington, Kan.

Just after 2 p.m. on Jan. 13, officials at the Wolf Creek Nuclear Operating Co., declared a Notice of Unusual Event after the failure of a main generator electrical breaker, followed by an unexplained loss of power to an electrical transformer. This caused the switchyard to become de-energized, which removed the plant’s connection to the electrical power grid. The emergency diesel generators automatically started and powered safety-related equipment. An Unusual Event is the lowest of four NRC emergency categories.

At 5:09 p.m. on January 13, Wolf Creek terminated the Unusual Event after off-site  power was partially restored. Plant personnel are continuing to investigate the cause of the  failure and determine necessary repairs. There were no radiological releases due to the event.

NRC resident inspectors responded to the control room to monitor site activities during  the event and were onsite last weekend to monitor licensee activities and initial recovery actions. AIT’s are used by the NRC to review more significant events or issues at NRC-licensed facilities. The six-member team has assumed responsibility from the resident inspectors for gathering information about the shutdown event and will travel to the site in the coming weeks.

The team will include inspectors from the NRC’s Region IV office, NRC Headquarters in Rockville, Md., and resident inspectors from other plants. The team will be led by NRC Region IV Branch Chief Mark Haire of the Division of Reactor Safety.

“An AIT is used when the NRC wants to promptly dig deeply into the circumstances surrounding an operational event,” said NRC Region IV Administrator Elmo E. Collins. “We want to make sure that all of the circumstances that contributed to this event are well understood in order to prevent a recurrence.”

The team will put together a detailed chronology of the event, evaluate the adequacy of licensee actions in response to the incident and assess the impact of the prolonged loss of off-site power to non-safety related equipment. The team’s report will not contain inspection findings, but will identify areas for further inspection follow-up.

The NRC will hold a public exit meeting with the licensee upon completion of the inspection to discuss its preliminary findings. The meeting will be open to interested members of the public and the news media, and team members will be available to answer questions after the results are presented. The AIT will also issue a written report within 30 days of completion of the inspection.

 

Source: NRC

Source: Power Engineering

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