Las Vegas Sun

March 29, 2024

UNLV scientists asked to study Yucca radioactivity

AMARGOSA VALLEY -- The Energy Department has signed an $850,000 contract with the University of Nevada, Las Vegas, to find out where radioactive chlorine found at the proposed nuclear waste repository site at Yucca Mountain originated.

The new contract, announced at a meeting of the Nuclear Waste Technical Review Board earlier this month, may settle a dispute between two Energy Department laboratories.

DOE scientists discovered Chlorine-36 in earthquake faults and fractures inside the mountain, 90 miles northwest of Las Vegas, in 1998. Los Alamos National Laboratory scientists said the radioactive chlorine came from atomic bomb tests in the Pacific Ocean in the 1950s. They said the chlorine had been carried by rain clouds to Nevada, then traveled with rainwater into earthquake faults almost 1,000 feet inside the mountain.

Follow-up tests by Lawrence Livermore National Laboratory indicated the chlorine did not come from atomic weapons, but from cosmic rays crashing into the atmosphere and entering the repository, research geologist James Paces of the U.S. Geological Survey said.

The source of the chlorine could make an important difference in determining the safety of Yucca Mountain as a site to contain 70,000 tons of the nation's high-level nuclear waste.

Both the Nuclear Regulatory Commission, which must license Yucca before a repository is built, and the technical review board are concerned that the fast pathways allowing contaminated rainwater into the mountain could threaten the integrity of the repository.

If the chlorine came from nuclear weapons tests in the Pacific, it moved through the Yucca Mountain rock to the depth where the Energy Department plans to bury nuclear waste in less than 50 years. A Yucca Mountain repository is supposed to prevent radiation from escaping into the environment for 10,000 years or more.

Nevada officials, who oppose the repository, say that that if the chlorine is from the nuclear tests, that could be important in their battle to halt the nuclear dump.

Energy Department officials said that while the university's study is under way, their ongoing work to design the repository will compensate for water from the mountain's surface flowing rapidly through earthquake faults and fractures.

Paces insisted the chlorine originated from cosmic rays. But Los Alamos geochemist Robert Roback said the latest test results show the chlorine came from nuclear weapons and one sample recorded the highest level of the chemical in five years of study at Yucca.

"They're tough measurements," Paces said. "I think there is an answer and we will find it."

Results of further tests by the two Energy Department labs, reported at the board's meeting in Amargosa Valley this month, did not settle the issue and the scientists continue to argue.

"We're not there yet," Roback said. "Perhaps a third party is the best thing yet."

That is the reason UNLV has been asked to conduct its tests.

Klaus Stetzenbach of the university's Harry Reid Center for Environmental Studies is leading the university's team effort, which includes chemists and geologists who could take 18 months to complete an independent analysis of the chlorine.

Although the university's research may offer a clue to the chlorine's source, the design of the repository will include estimates of rapid water flows through the mountain, said Bill Boyle, the Energy Department's director for licensing and repository safety after it closes.

"Whatever it is, it is something not immediately obvious," Boyle said. "Whatever it is, it is a difficult measurement."

The Energy Department's Bo Bodvarsson, who is studying the rate of rainwater flowing through the mountain, said, "We still do not know the details of the flow."

Donald Shettel, a hydrologist contracted by the state, said the Energy Department has other issues besides Chlorine-36 to address, especially when it comes to how fast buried nuclear waste containers will corrode.

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