109 Radioactive Storage Casks Undertested Before Use

Article published Aug. 13, 2009

NRC: Dry cask test was eliminated

By Louis Porter Vermont Press Bureau

MONTPELIER – The concrete-and-steel "dry casks" used at the Vermont Yankee plant to store spent nuclear fuel were not tested as completely as they should have been, according to federal regulators.

But the decision by Holtec International, the New Jersey company that built the casks, to omit one set of tests does not pose a safety risk, Nuclear Regulatory Commission officials said Wednesday. That's because there were other kinds of inspections done on those casks, and the waste stored in the casks is not as hot as allowed, meaning they are safe even though they were not tested with pressurized helium as required under a federal licensing agreement.

About 109 of the casks that were not completely tested are in use nationwide, including five at Vermont Yankee, regulators say.


"The violation is a concern" because the canister "is relied upon to prevent the release of radioactive material," according to a letter from the NRC to Holtec. "It is also relied upon to maintain an inert environment and sufficient helium pressure to keep cladding temperatures below the acceptable limit."


While the NRC puts the responsibility for the cask inspection problem on the New Jersey company that made them — not on Vermont Yankee — the matter is the second problem associated with the dry casks recently. In an unrelated matter, it was discovered that the plant was not doing as much radiological monitoring of the dry casks as was required by an agreement with the state. The plant was still monitoring temperature of the casks, and the failure to establish a radiation monitoring process was due to "a lack of formal tracking of such state commitments," according to Vermont Yankee.


The dry casks in which Entergy and other nuclear plant operators store spent fuel consist of a half-inch thick stainless steel tank that is welded shut. Those welds are inspected and are X-rayed to ensure they don't leak. The casks are placed inside another steel-and-concrete tank, filled with spent fuel that still generates heat, and then filled with helium.


However, Holtec was obligated also to use pressurized helium to test and ensure the tanks did not leak even a few molecules at a time before they were put into use, according to the NRC. After many of those tests showed no leaks, the practice was discontinued by the company, according to NRC officials.


The company "did not legally comply with our legal requirements" said Ray Lorson, deputy director for technical review of spent fuel storage and transportation for the federal regulators.


But, he added, "we believe that the systems that are out there are operating safely."


Raymond Shadis, a technical adviser to the New England Coalition, said the elimination of the helium-pressure testing of the dry casks, despite the successful record of those tests in the past, is worrisome for several reasons.


It was evidence of "a trend in the nuclear industry to operate on the belief that safety margins are excessive and that one can reduce them or take chances in not going the full distance," he said. Those safety margins are put in place for good reasons given the scale of the potential harm from the release of nuclear material, Shadis added.


Testing with helium also is important because gas can escape through tiny holes, or even through some materials. Shadis said the helium in the dry casks, when they are loaded with spent fuel, acts as a medium to circulate and release heat; the fuel inside the cask can be 750 degrees Fahrenheit, according to the NRC.


"Helium is notoriously hard to contain," Shadis said. "If you don't have the full volume of helium in there, you will have no medium in which to circulate that heat."


That could lead to much more serious problems, Shadis added.


Holtec, which did not respond to a request for comment Wednesday, has returned to testing its new casks with helium and must report back to the NRC about how it will deal with the inspection problem. But it is unlikely the casks already loaded with spent fuel will be opened and their contents put into new receptacles, NRC officials said. That's because the exposure of workers while moving the fuel is an unnecessary risk, Lorson said.


However, the other dry casks made by Holtec that are at the Yankee site but have not yet been used will be inspected with helium by the company, NRC officials said.


"While the issue is between Holtec and the NRC, the subsequent Holtec engineering analysis demonstrates the casks in use across the country maintain their integrity and pose no risk to personnel health and safety," said Vermont Yankee spokesman Rob Williams by e-mail. "Our five Holtec casks in use on the Vermont Yankee site have functioned normally with no evidence of any problems."



For related story, go to: www.vermontguardian.com/local/0105/CaskWarning.shtml