Test sheds light on waste storage

Benjamin Grove

Wednesday, June 25, 2003 | 11:29 a.m.

ROCKVILLE, Md. -- Scientists who loaded nuclear waste into a metal storage container in 1985 and opened it up nearly 15 years later discovered no evidence of container stress or decay, a Nuclear Regulatory Commission official said.

While the experiment offered some new insights, it's not clear the test has much relevance to Yucca Mountain, experts said.

For an experiment unusual in its scope and duration, scientists took waste from the Surry nuclear power plant in Virginia and loaded it into a cast-iron Castor V-21 brand waste container, along with sensors for temperature and other readings. While the waste was the kind that ultimately would be stored at Yucca Mountain, the container was not. Department of Energy officials plan to use a high-tech metal alloy waste container at Yucca, the site of the the proposed national high-level nuclear waste repository.

Still, the experiment shed some new light on how waste decays inside a storage container and how "dry cask" storage containers -- now in use at power plants nationwide -- contain waste.

Harold Scott, a scientist with the NRC Office of Research, today presented the experiment results to the NRC's Advisory Committee on Nuclear Waste, which advises the five-member Commission on Yucca issues.

High-level nuclear waste is in the form of fingertip-sized solid uranium pellets. The pellets are arranged in thin, metal 12-foot rods. The rods are bundled together and used to generate electricity in a nuclear reactor. When the rods are "spent," they are removed from the reactor as highly radioactive waste. The rods are typically put in cooling pools for several years and then loaded into waste containers.

When scientists at Idaho National Engineering and Environmental Laboratory opened the test container in 1999, they launched experiments on four rods from a bundle stored near the middle of the massive container, Scott told the NRC panel.

They discovered the fuel pellets and the metal rods had not cracked or released unusual amounts of dangerous gases, Scott said. As waste decays, it releases heat, and scientists had arranged the experiment so that the temperature inside the waste container would approach 400 degrees Celsius, the NRC-standard limit for the container, Scott said.

The container itself was completely intact, and there were no signs the cask would fail in another 20 or 40 years, Scott said.

"The cask didn't leak," Scott said after his presentation to the panel. "They didn't find anything strange or damaged in the cask or the (fuel-rod) basket."

Several of the waste panel members discussed whether the experiment had relevance to Yucca Mountain, where waste would be stored for 10,000 years or more. But they generally agreed that it was difficult to apply conclusions from the experiment to waste containers that would be used in the underground tunnels at Yucca.