Nuke waste containers corrode in water test

Mary Manning / Las Vegas Sun 29may01

Energy Department scientists are wrestling with potential weaknesses in the metal chosen to store highly radioactive waste in a proposed repository at Yucca Mountain.

The alloy that will make up containers holding rods of spent nuclear fuel showed signs of corrosion after worst-case exposure to water from the mountain, DOE scientists told a seven-member scientific review team last week in Las Vegas.

Yucca Mountain, 90 miles northwest of Las Vegas, is the only site being studied to hold 77,000 tons of waste from nuclear power plants and defense activities.

The mountain must be proven safe for a repository, and so far no studies have presented insurmountable obstacles, according to a DOE report on the research released last month.

The DOE is expected to make its recommendation on Yucca Mountain later this year. An independent scientific team began reviewing DOE's work on proposed nuclear waste containers last week. The team expects to finish its final report by April, Chairman Joe Payer said.

The containers made of C-22 alloy are considered the first line of defense to protect the environment and nearby residents from radiation. The mountain's volcanic rock is the other.

Scientists also are researching the potential for water to reach the repository level and for radiation to escape the mountain through ground water.

The containers are being designed to keep the highly radioactive spent fuel and defense wastes intact for 10,000 years, the planned lifetime of the repository.

The metal planned for the containers has been used in corrosive environments such as pulp bleaching and flue gas stacks, said Gerald Gordon of Framatome Advanced Nuclear Power, a DOE contractor. A sheet of an earlier form of the metal exposed to sea air since 1941 is still shiny, he said

However, in some laboratory tests using water from a well near Yucca Mountain containing lead, arsenic or mercury, some stress cracks in the metal were recorded, he said.

The temperature of the water was above boiling -- 212 degrees Fahrenheit -- in the experiments, Gordon said. Other studies have predicted that the preferred design for a repository would allow the mountain to get that hot.

In September scientific consultants for Nevada who studied the metal alloy said C-22 corroded in samples of the same water in 14 days.

The danger of corrosion from water inside the desert mountain is not remote.

Although the repository would be built 500 feet above the water table, the mountain's pores and cracks contain plenty of water, Gregory Gdowski of the Lawrence Livermore National Laboratory, said. "That is quite a bit of water you can generate."

The water, as it flows through Yucca's rock, could become saltier, possibly corroding the metals proposed for containers, he said. It can also bring naturally occurring lead, arsenic or mercury into contact with the containers, speeding corrosion, Gdowski said.

In addition to water, scientists have discovered organisms in Yucca's soils that can live in high heat and salty water. Some of the microbes can eat through carbon steel, which would be used for frames holding the containers, Gdowski said.

"There are bugs in the mountain," Gdowski said. They can survive temperatures up to 140 degrees Fahrenheit, considered warm, but not boiling water, he said.

While radiation from nuclear waste buried in the mountain is expected to kill those organisms, water seeping into the drifts where the containers could bring more microbes, he said.