A ship loaded with nearly 6,000 tons of radioactive soil is trapped in the ice off McMurdo Sound, site of a U.S. military research station in the Antarctic waiting for an early spring thaw to release it.

The frozen cargo carries one of the final visual reminders that a nuclear-powered reactor once existed at the site. Created to provide electricity for a research base in the Antarctic, the reactor was closed down in 1972 after 11 years, the longest continuous run for a military reactor. At the time, the Navy said the reactor had run its useful course. But numerous malfunctions and leaks reported in the Navy's decommissioning plan and subsequent reports have raised questions about the Navy's ability to protect the health and safety of its personnel as well as the fragile environment of the Antarctic.

Antarctica, in its icy remoteness from the rest of the world and by treaty agreement has been able to defend its pristine environment from radioactive pollution. The United States, as a signer of the Antarctic Treaty, has agreed that nuclear materials may be brought into the Antarctic and used experimentally, but then must be removed.

According to Navy Admiral William M. Zobel, vice commander of the facilities, "There was no risk to personnel. We're just talking about being supersafe getting that stuff out of there. There were traces of radioactivity, and the Antarctic Treaty called for no traces of radioactivity to be left in the Antarctic."

The Dismantled reactor and spent fuel roads were shipped to a radio active storage site in Georgia for burial. Nearly 14,000 tons of low-level irradiated soil were dug up and transported for disposal at Port Hueneme, a naval base north of Los Angeles.

The dismantling of the McMurdo reactor sharply contrasts with the optimism which prompted Congress in 1960 to authorize its installation at the naval base. McMurdo Naval Air Facility roughly midway between New Zealand and the South Pole, was the logistics headquarters for Operation Deep Freeze, a scientific research program being conducted in the Antarctic.

In 1961, a nuclear-powered reactor to generate electricity seemed the ideal choice because oil fuel was expensive, alternative energy source were not available and because there was no large population nearby to worry about.

The McMurdo reactor was located on a small volcanic ash cone terace a few hundred yards away from the base. It was about 25 miles from the still active crater of Mt. Erebus.

Because subzero temperatures made pouring and curing of concrete as an underground protective shield difficult, crushed gravel was substituted. Lead shielding was wrapped around most of the radioactive parts to keep the heat from melting the ice in the surrounding soil. But from initial construction to final decommissioning, the reactor was plagued with problems.

Shortly after it began operation, a hydrogen fire in the containment tanks forced the reactor to be shut down for two months. Cracks which later appeared in the containment vessels had to be welded. Dr Robert Anderson of San Jose State University, who later studied the radioactive levels of the soil for the California Waste Board, said the welding did not close the cracks until some of the radiocative coolant had been lost.

According to another report, some radeoactive effluents, which had been diluted with brine to keep them below the miximum concentration allowed by the federal government, still became concentrated in the soil.

At the time the reactor was shut down in 1972, there was some concern that a spill had taken place. But until the Navy decommissioning plan revealed that some leakage has indeed occurred, the U.U. Antarctic Journal reported simply that the reactor had been shut down agter routine inspection reaveled wet insulation had been found around some pipes.

The Secretary of the U.S. National Academy of Sciences committee on polar research was more to the point: "The reactor was shut down because of numerous malfunctions and its pollution potential."

Although Navy procedures called for removal of all contaminated structures, the Nuclear Regulatory Commission required that, in addition, all radioactive contaiminated soil be removed as well. The last ship loaded with a cargo of frozen soil should begin its 19-day journey half way around the world by this March.

While the currently-stranded ship waits to resume its journey, its crew sits on top of a radioactive cargo which is similar in content to the soil alrady under asphalt wrap at Port Hueneme.The soil, according to a study completed last summer, is considered "harmless", but is not suitable for agricultural use or use in areas of continous contact.