Saturday, August 13, 2005
Copyright © Las Vegas Review-Journal

YUCCA MOUNTAIN: 'Monkey wrench'

Report: DOE hasn't fully studied how to handle damaged fuel assemblies

The Energy Department says it could be 2012 or later before the Yucca Mountain complex will begin accepting spent nuclear fuel for burial. Photo by John Gurzinski. Click image for enlargement. Work continues on the Yucca Mountain repository, which is years away from accepting spent nuclear fuel. Photo by Gary Thompson.

WASHINGTON -- Thousands of fuel assemblies containing radioactive nuclear waste are expected to arrive damaged at Yucca Mountain, including some with undetected leaks and cracks, posing potential risks to workers and the public, according to a report prepared for the government.

Handled without special precautions, fuel with damaged cladding that is extracted from protective canisters and exposed to the air could trigger chemical reactions, causing gases to escape and fuel pellets to oxidize into micron-sized dispersible powders.

The released powders would result in "high levels of radioactive contamination" in fuel-handling areas of the repository complex, Energy Department and contractor engineers concluded in a study completed in March. The Review-Journal obtained a copy through the federal Freedom of Information Act.

Only months before the department has said it may apply for a license to build a Yucca Mountain complex, the engineers concluded DOE had not fully evaluated the hazards associated with handling damaged fuel at the site, nor designed processes for managing it effectively.

Experts outside DOE expressed surprise.

"It is rather late in the day for these people to be thinking about this stuff," said Arjun Makhijani, a nuclear engineer and president of the Institute for Energy and Environmental Research. "It is truly astonishing that they have not thought about this issue thoroughly a quarter of a century after serious work on repositories began.

"This is a big deal. It throws one more monkey wrench into the process of what issues are resolved and not resolved."

The Department of Energy wouldn't provide a representative to be interviewed about the topic but supplied written answers to e-mailed questions.

"There have been a lot of meetings on this," a DOE official said on condition of not being identified. "You are talking about design, and you can't have a license application without a design."

The report identified areas where more research was advisable. They include the rates at which fuel might degrade into powder form, potential worker doses, and whether under any circumstances oxidized fuel could provoke a nuclear chain reaction.

"The process for handling failed fuel in damaged fuel cans is not yet detailed in current design documents, and the related hazards have not yet been evaluated," the report's authors said.

DOE managers believe the matter can be addressed, "but it gets into cost and other things -- like time -- depending on the design," an official said. "They know what to do. It's a question of how they want to do it and what will be required. And I'm sure the schedule has come up."

DOE officials earlier this year abandoned a 2010 opening date for the repository, saying it could be 2012 and possibly later before Yucca Mountain could begin accepting spent fuel for burial.

Among the options DOE is considering, according to officials familiar with the issue, is adding a pool on the repository grounds so damaged fuel rods can be handled underwater, as they are at nuclear power plants.

In its written responses, the DOE said it was planning "confinement cells that include thick concrete walls and air locks to protect the worker and the public from exposure to radiation."

At a June 6 public meeting in Pahrump, DOE official Richard Craun said managers were working on designing rooms where oxygen would be pumped out and replaced with nitrogen to create an inert atmosphere in which to handle problem fuel.

"As a conservative measure, DOE will handle all assemblies in confinement cells, whether damaged or not, to ensure the safety of the worker and the public," the department said in its written replies.

"Operations may occasionally be interrupted to facilitate confinement cell cleanup. Potential risk to the worker and the public from repository operations are well within established federal radiation protection standards."

DOE added it was considering "other design and operational practices that would further prevent or mitigate the release of radionuclides. DOE is evaluating the various options described in the report for inclusion in the license application."

Potential fuel oxidation at Yucca Mountain has become a priority topic that the Nuclear Regulatory Commission is monitoring as it awaits DOE's repository licensing request, Tim Kobetz, an NRC senior project manager, said at an Aug. 4 advisory board meeting.

NRC staff is preparing an evaluation of the issue, anticipating it could be raised during Yucca license hearings.

"Fuel oxidation is definitely a potential risk," said Marissa Bailey, engineering section chief in the NRC's division of high-level waste repository safety. "It is something (DOE) will have to address in the license application."

Nuclear utilities deal with damaged fuel on a regular basis, and it has been studied extensively, said Dan Bullen, an engineering risk consultant and former member of the Nuclear Waste Technical Review Board, which evaluates Yucca Mountain science.

Even though Yucca Mountain would be a first-of-its-kind facility, Bullen said, he believed DOE could minimize risks. Over 25 years that fuel would arrive at the site, the number of damaged assemblies would be small, he said.

"If they keep it in an inert atmosphere, it will not be a problem; and I would agree with that," Bullen said. "I don't want to say it is easy, but it is a realistic engineering approach."

Steve Frishman, a full-time consultant for the state of Nevada, said, "Given time and enough experimental work, they can probably figure out how to run an industrial operation which doesn't have the risk of high exposures which they say are unacceptable.

"But either way, they haven't got enough knowledge of design of fuel transfer at this point to have a license application in six months," he said.

Bob Loux, director of the Nevada Agency for Nuclear Projects, said DOE appears to have overlooked an issue important to safety.

DOE "has not thought through the issues of the surface operations, from what we've seen," said Loux, who coordinates Nevada's official opposition to the repository.

If DOE decides to install spent fuel pools, it would open a new set of questions about earthquake vulnerability, Loux said.

Sen. Harry Reid, D-Nev., said the report shows evidence of project flaws and more reasons why it should be ended.

"At no point while moving waste off site, to transportation to proposed storage, can DOE protect workers and communities from being exposed to dangerous levels of radiation," Reid said. "New so-called standards were released this week for supposedly a million years into the future; but according to this latest report, DOE can't even figure out how to remove the waste from plant sites safely."

While much public attention has been focused on the projected performance of an underground Yucca repository over thousands of years, nuclear waste would be handled routinely at an industrial complex on the east side of the mountain.

There, waste-bearing shipping casks arriving by train and truck would be unloaded, unpacked and repackaged into burial containers or aging canisters. Although the tasks would be handled by machinery and robots, workers would be present.

Spent fuel assemblies are expected to arrive at Yucca Mountain at a rate of about 9,000 a year, or 222,000 assemblies over 25 years.

The fuel study said about 4 percent, equating to 8,880 assemblies, "are expected to have varying amounts of cladding damage that could lead to fuel oxidation when the assemblies are handled in air."

Each of the damaged assemblies is expected to have an average of 2.2 failed fuel rods, the study said.

Most of the damaged fuel will be identified through reactor records, "but a small percentage of assemblies (approximately 0.4 percent or 1,000 fuel assemblies) is expected to have unknown or undetected cladding damage that could allow the fuel to oxidize."

During handling operations, a typical assembly is expected to be exposed to the air for more than 100 hours at temperatures up to 400 Celsius, the study stated.

"At these times and temperatures, fuel oxidation is expected for failed fuel during normal waste handling operations," the study stated.

The rate of oxidation would depend on time and temperature.

Frishman said the report appeared to show that damaged fuel cladding at the 400 Celsius temperature could be susceptible to failure after two hours of exposure to air.

DOE officials didn't comment on that point Friday.

During the oxidation process, the oxidized fuel would swell and could cause further failure, a process called "clad unzipping."

"The contamination levels and dose rates resulting from normal handling of commercial spent nuclear fuel are expected to be much higher than desirable," the study stated. "Oxidized material released from fuel rods will be difficult to control and account for."

According to government scientists, a preliminary analysis concluded the amount of oxidized material that would be released would not pose concerns for criticality, or a nuclear reaction. "However, the uncertainty with oxidation rates and release fractions needs further evaluation to determine if this preliminary analysis is conclusive," it said.

Bailey said the potential for criticality "is pretty low, because they are handling fuel in a dry environment. There is not an issue of criticality."