Xcel Energy seeks license amendment to address Monticello nuclear plant dry cask weld inspection

Xcel Energy is seeking a license request change to solve a weld inspection issue that’s dogging dry cask storage at the Monticello Nuclear Generating Plant.

Tim O’Connor, Xcel Energy senior vice president and chief nuclear officer, and Karen Fili, site vice president, appeared before the Monticello City Council Monday night to provide a plant update.

O’Connor said Xcel Energy officials had a meeting scheduled today (Wednesday, May 14) with the Nuclear Regulatory Commission (NRC) in Washington, D.C. to discuss a licensing amendment related to dry cask storage.

During the plant’s March 31 end-of-cycle assessment meeting the NRC addressed concerns with dry cask storage at the plant’s independent spent fuel storage installation (ISFSI).

Currently, the Monticello plant has loaded 16 dry fuel storage canisters. Dry cask storage allows spent fuel that has already been cooled in a nuclear plant’s spent fuel pool for at least one year to be surrounded by inert gas inside a container called a cask. The casks are typically steel cylinders that are either welded or bolted closed.

The steel cylinder provides a leak-tight confinement for spent fuel. Each cylinder is surrounded by additional steel, concrete, or other material to provide radiation shielding to workers and members of the public. Some of the cask designs can be used for both storage and transportation.

Last October, the NRC determined that weld tests were performed improperly on one canister. Subsequently, Xcel Energy identified five additional canisters with improper weld tests within the ISFSI and one in the plant. The NRC is confident the casks are leak-tight because multiple additional tests were performed on closure welds.

The casks are subject to radiation monitoring. O’Connor said Monday night that a “vendor deficiency” had been identified in the course of welding the storage canisters shut.

“We can’t perform one of the inspections that’s required of our license, and we have to ask the NRC for an exception,” O’Connor said. “It’s our belief that taking the canisters apart would not be in the best interest of employees, the community or people who are doing the actual activity.”

This graphic shows the inside of a dry fuel storage canister. Opening up certain dry cask storage canisters or repackaging the spent fuel inside or partial canister disassembly aren’t options Xcel Energy wants to consider at the Monticello Nuclear Generating Plant, said Tim O’Connor, Xcel Energy senior vice president and chief nuclear officer. (Graphic Courtesy Xcel Energy)

This graphic shows the inside of a dry fuel storage canister. Opening up certain dry cask storage canisters or repackaging the spent fuel inside or partial canister disassembly aren’t options Xcel Energy wants to consider at the Monticello Nuclear Generating Plant, said Tim O’Connor, Xcel Energy senior vice president and chief nuclear officer. (Graphic Courtesy Xcel Energy)

O’Connor explained the lids on the top of each canister are stacked on top of each other. A dye penetrating test is supposed to be done when welds are completed.

“The dye penetrant test was not performed in exact accordance with procedure, so we can’t credit it as sufficient or certified,” O’Connor said. “That’s created a license non-compliance with the NRC, he added.

According to O’Connor, Xcel Energy has sufficient technical evidence that all of the welds are of the right size and were done properly. “The visual inspections were done correctly; the dye test wasn’t,” he said.

“We can demonstrate through a license request change that the canisters are solid,” O’Connor said. “They were installed appropriately. The design and construction of the work that was done does meet code. We’ve done pressure tests and weld failure analysis.”

O’Connor told the council there isn’t an issue with the welds, only the post-weld inspection. He added the canisters have been tested to extreme conditions.

Last July, Xcel Energy completed a three-month refueling outage that included substantive and extensive plant modifications to support a hike in capacity to 671 megawatts. On Dec.10, 2013, the NRC approved Xcel’s request for an extended power uprate (EPU) to raise the plant’s power production by 13 percent.

During Monday night’s council meeting, Fili said the Monticello plant is currently operating at 89 percent power. “During the 2011 refueling outage, we replaced a steam dryer specifically designed to last the rest of the plant’s life,” she said.

“When we were monitoring the steam dryer, we determined that some of the strain gauge data was swapped on one of the main steam lines. This information was questioned by the NRC,” Fili said.

Westinghouse Electric Co. removed Monticello’s original steam dryer from the nuclear reactor and installed a state-of-the-art replacement during the 2011 refueling outage.

The installation of the massive piece of equipment represented the first boiling water reactor (BWR) replacement steam dryer installed by Westinghouse at a U.S. plant.

Steam dryers are used during the final stage of moisture removal to provide the high-quality steam to the plant’s generating turbine. The one-piece assembly is 17 feet in diameter, 16 feet tall and weighs 60,000 pounds.

Fili said Monday that Westinghouse was re-evaluating the Monticello Nuclear Generating Plant’s steam dryer data. “It’s correct on three of the four steam lines, but on the fourth line, the upper and lower strain gauges were swapped,” Fili explained, adding that investigation by the Monticello plant staff identified configuration errors in the data acquisition equipment software and physical wiring of some strain gauges.

In an interview before Monday night’s Monticello council meeting, O’Connor said prior to identifying the analysis issue with the steam dryer, Xcel Energy thought it might be at full EPU power by June.

“Now, we are looking more towards the end of the year,” he said.  “We’ve certainly seen a delay factor as a result of this re-evaluation. One of the good things about working with Westinghouse is they have this type of steam dryer in service overseas.”

Opening up the dry cask storage canisters or repackaging the spent fuel inside or partial canister disassembly aren’t options Xcel wants to consider, he said.

“They are both negatives,” O’Connor said. “The first option is we take them completely apart. When you start disassembling canisters, no one is quite sure if we can reuse them. We could take them completely apart, and end up with scrap. Then, we’d have to put the spent fuel back in the pool [inside the plant].”

O’Connor added: ” Nobody is happy with the fact that we had a supplier not perform to the highest degree, but the question becomes, is that deficiency, with all the barriers that are in place, significant enough to say disassemble? Our belief is no, and we can give evidence to support that case.”

O’Connor said that Xcel Energy has consulted with the U.S. Department of Energy, the Nuclear Energy Institute and Areva Corp. the company that manufactured the storage canisters.

“The real issue becomes if we have to take a direction that the NRC decides we need to embark on that we haven’t currently thought of, or they say, ‘No, take them apart.’ What we don’t want is placing a brick wall between the parties that have to remedy the problem,” O’Connor said. “Our position is we’ll work with our vendors to solve the problems, then afterward, we’ll determine who owes what.”

O’Connor said it was important for Xcel Energy officials to talk to Monticello city leaders before heading off to Wednesday’s meeting in Washington, D.C.

“I don’t think it’s right that we should be talking to the NRC without letting our community know first what we are thinking,” he said, adding that the utility wanted to explain why and what it was doing, especially since the dry fuel storage weld test problem was a discussion item that held interest at the March 31 meeting.

“We want to be trusted partners with the community,” he said. “Xcel Energy thinks the only way to work with people is tell them what the facts are, and tell them what we did right, what we didn’t do right, and what our corrective actions are going to be.”

Contact Tim Hennagir at tim.hennagir@ecm-inc.com

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