VY spent fuel casts not fully tested
BRATTLEBORO -- A failure to test the dry casks used to store spent nuclear fuel at Vermont Yankee nuclear power plant in Vernon does not present a danger to the public's health and safety, said a Nuclear Regulatory Commission official during a teleconference with the media on Wednesday.
The NRC recently discovered that Holtec, which manufactures the "HI-STORM 100" dry cask, was not conducting a helium-leak-rate test as required by NRC regulations.
About 200 of the casks were not tested, five of which are holding 340 fuel assemblies on a concrete pad just north of the Yankee reactor building.
The NRC "has reasonable assurance that none of the casks involved are leaking or will leak," according to a statement released by the NRC.
A Yankee spokesman said Holtec's failure to conduct the test did not impact the integrity of the casks.
"Cask welds were made by qualified welders, using qualified procedures and qualified weld material and were subjected to other quality control tests and radiography prior to shipment from the factory," stated Rob Williams, spokesman for Vermont Yankee, in an e-mail to the media.
Holtec eliminated the pressure test after it concluded that previous tests and its welding procedures had proven the casks wouldn't leak. But Holtec's decision to eliminate the test was a violation of NRC regulations and it was advised to reinstate the testing procedure until the NRC determines if the test is no longer needed.
"Holtec should have come to us before making the change," said Ray Lorson, the deputy director for technical review in the division of spent fuel storage and transportation, during the teleconference. "We required that they take immediate corrective actions."
Of the casks already in service, said Lorson, "None of the canisters had approached the limits we license them to."
By NRC regulations, the maximum internal temperature of the casks cannot exceed 750 degrees, or 27 kilowatts of heat. Yankee's casks don't exceed 10 kilowatts of heat, said Lorson.
On Aug. 11, Entergy checked the casks and found no evidence that radiation was leaking from any of the five, he said.
The five casks in service at Yankee "have functioned normally with no evidence of any problems," stated Williams.
The spent fuel is stored in an inner sleeve made of one-half-inch-thick stainless steel in an atmosphere of helium seven times the pressure of the outside air. The inner sleeve itself is inside an "overpack," a large cylinder with several inches of concrete and its own stainless steel liner.
The dry casks are six feet in diameter and stand 14 feet tall.
The helium pressure test is meant to ensure that welds used in cask construction are structurally robust and capable of retaining the helium, which is meant to limit corrosion of the fuel assemblies.
There are 109 casks at 15 sites in the United States that weren't checked using the helium-leak-rate test, said Neil Sheehan, spokesman for the NRC. Holtec stopped testing them sometime in 2006. Casks that have not yet been placed in service will be subjected to the tests.
Conducting the pressure test now would mean moving the casks back to the reactor building and unloading the fuel, exposing workers to an unnecessary dose of radiation, said Lorson.
"That's not a smart move given that there's no safety concern," he said.
Bob Audette can be reached at firstname.lastname@example.org, or at (802) 254-2311, ext. 273.
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