The Nuclear Regulatory Commission has cited the PPL Susquehanna nuclear power plant for a violation of regulatory requirements that govern the plant's dry cask storage system.
"Our first priority at all times is to keep the public and our employees safe," said Herbert D. Woodeshick, PPL special assistant to the president for Susquehanna. "As soon as we discovered this incident, we corrected the situation, conducted a thorough investigation and instituted new procedures to prevent it from happening again."
"We have cooperated with the NRC throughout its investigation of this matter, and we respect the commission's decision in determining that the incident constituted a Level III violation," said Woodeshick. "In reaching its conclusion, the NRC did acknowledge that we promptly identified and evaluated the situation and that the event did not represent an immediate safety concern."
In its report, the NRC also said the incident appeared to be isolated. However, the commission decided to classify the event as a Level III because the situation placed a dry shielded canister in an "unanalyzed condition" that required a detailed evaluation to demonstrate that there would not have been any long-term effects. "The PPL evaluation conclusively demonstrated that the event did not represent any immediate or long-term threats to employees, used fuel, station operation or the public," Woodeshick said.
The NRC credited Susquehanna for the identification of the event and for the actions taken to correct the violation and prevent its recurrence, and therefore did not recommend a fine.
In July, while preparing a canister to transport used nuclear fuel from the plant's spent fuel pool to the plant's dry storage system, plant personnel inadvertently filled the steel container with argon gas instead of helium gas.
The problem was discovered before the canister was removed from the reactor building, and the NRC was notified immediately.
Both gases are used to prepare the container for storage. Since used nuclear fuel continues to generate heat, both the fuel pools and the dry storage system are designed to cool the fuel. Helium is used to fill the dry storage canister because it does the best job of transferring heat from the fuel to the canister.
"Although calculations done using argon indicated that it did not compromise the safe storage or handling of the used fuel, we took a conservative approach to the situation and decided to replace the argon gas with helium," Woodeshick said.
PPL Susquehanna has been using dry fuel storage since 1999. During a transfer, plant personnel load stainless-steel canisters with used fuel bundles that have cooled for a minimum of five years in the fuel pool. Each canister is filled with helium to prevent corrosion and to allow for heat to transfer. Workers use argon to weld the canister shut. The canister is then placed inside horizontal, concrete storage modules located inside plant security fences. Each module is sealed and continuously monitored.
The dry cask storage area was designed to safely store used nuclear fuel until the federal government builds a permanent repository. Congress recently cleared the way for the Department of Energy to apply to the Nuclear Regulatory Commission for a license to build a centralized storage facility at Yucca Mountain, Nev. The earliest expected opening date for the facility is 2010.
The 2,248-megawatt Susquehanna plant, located in Luzerne County, Pa., is owned jointly by PPL Susquehanna and Allegheny Electric Cooperative Inc. and is operated by PPL Susquehanna.