A tank connected to a portable nuclear reactor once used to power an Air Force radar station near Sundance during the Cold War apparently leaked radioactive material, and officials now are studying to see if the site must be cleaned up.

The site near the top of Warren Peak was added to the Federal Agency Hazardous Waste Compliance Docket on Jan. 2, in the Federal Register.

Under the Army's Nuclear Power Program, portable nuclear reactors were developed and installed in remote locations, including Camp Century, Greenland; McMurdo Station, Antarctica; Fort Greely, Alaska; the Panama Canal Zone and seven miles north by northwest of Sundance.

Tim Pavek, a cleanup expert based at Ellsworth Air Force Base, said the Warren Peak radar base was one of 100 or so stations lined along the northern tier of states in the 1950s and 1960s. It was designed to detect missiles that might someday come over the North Pole from the Soviet Union.

Pavek explained that during the operation of the reactor, between 1962 and 1968, a 12,000-gallon tank holding contaminated water sprung a leak, washing cesium-137 downhill to the northwest.

"We've tracked it horizontally and after a few hundred feet, it disappears and can't be distinguished from the background level of natural radiation," he said.

The reactor and tank were removed in 1968.

Cesium-137 is produced spontaneously when uranium undergoes fission, according to the Environmental Protection Agency (EPA). It has a half life of 30 years, decaying back to barium. Exposure to cesium-137 can result in malignant tumors and shortening of life.

Jeff Mashburn, a policy analyst with the EPA Region 8 office in Denver, said the Air Force, EPA and Wyoming's Department of Environmental Quality are assessing the site - a process that will ultimately assign it a hazard score that will determine whether it gets cleaned up right away, gets cleaned up someday, or can be safely ignored.

Don Fischer, North District groundwater pollution control principal for the DEQ, said the assessment is wider than the cesium leak, looking at abandoned family housing, septic tanks, soil and water samples.

"The Air Force has put in several monitoring wells," Fischer said. So far, nothing especially troubling has shown up, he said - an assessment shared by Pavek and Mashburn.

Michelle Ramos, director of the Crook County Museum in Sundance, said the Warren Peak nuclear reactor is well known in northeast Wyoming.

"We have a scale model of it and a good-sized file about it," she said. The Air Force was apparently interested in testing the reactor design in the harsh winter conditions on Warren Peak, she said.

Pavek and Fischer said public meetings will be scheduled in Sundance as the assessment process continues.