Radiation warning alarms sounded last week at the Hanford Nuclear Reservation in Washington state, prompting a take-cover order that sent about 350 workers seeking shelter indoors during the demolition of a plant that for decades had helped make nuclear weapons.

The take-cover order – the second issued at the Manhattan Project legacy site in less than two months – was lifted about four hours later after low levels of radiation were detected at the reservation’s former plutonium-production plant, itself the site of a massive and decades long cleanup.

Though the US Department of Energy, which is responsible for the site, reported no injuries, the incident underscores the ongoing difficulties of containing the spoils of the Cold War faced by the US and Russia.

Officials for Hanford said in a release that the alarm was triggered while a glovebox was being removed from the site’s Plutonium Reclamation Facility, which is undergoing demolition. Gloveboxes are large pieces of material that were used when the plant was producing plutonium during the Cold War.

A worker preparing sections of a glovebox at the Hanford Site’s Plutonium Reclamation Facility for removal. (Photo: http://www.hanford.gov)

Low levels of contamination were detected outside the Plutonium Finishing Plant, including locations on sidewalks and near a vehicle access gate. Officials applied adhesive to the contamination to prevent its spread.

“Air monitoring alarms during demolition are not unexpected,” the Energy Department said in its release, noting the alarms are used to ensure demolition of the plant proceeds safely.

On Monday, workers were continuing to monitor the air for any further contamination. No other details were provided about the incident.

The latest incident followed the collapse last month of a tunnel at the facility that contained nuclear waste, prompting another evacuation. The Energy Department has said no injuries or contamination resulted from the collapse.

The tunnel – which is hundreds of meters long – houses a mixture of radioactive and chemical waste, as well as eight irradiated rail cars. The ground above the collapsed tunnel has since the incident been covered by a huge tarp and will eventually be filled in with concrete to prevent further incidents, the Associated Press reported.

Cleaning up radioactive materials at the Hanford site, which is roughly half the size of Luxembourg, has been one of the Energy Department’s priorities for years, and is expected to continue until 2060 at a cost of $100 billion on top of the $19 billion already spent at the site.

Hanford’s reactors produced about two-third of the plutonium used in American nuclear weapons until 1980. Since then its history has been one of calamitous radioactive contamination. Its plutonium reactor, the world’s first, contaminated the Columbia River.

Between 1947 and 1956, as the arms race between America and the Soviet Union ramped up, five new plutonium production reactors were added, as were two chemical reprocessing plants and 81 underground waste storage tanks. Hanford’s contamination stretched down the US Pacific Coast between 1950 and 1960 as all of its reactors ran at full capacity.

Then, in 1974, officials detected a 430,000-liter leak in one of the site’s waste storage tanks. Two years later, an explosion at the Plutonium Finishing Plant blew out a quarter-inch-thick window and showered a worker with nitric acid and radioactive glass.

The Hanford reservation’s shutdown was ordered as far back as the administration of Lyndon Johnson in 1964, but closure was stutter-step until 1988.

The current Hanford cleanup budget for this year is some $2.3 billion, with $1.5 billion of that going to manage and treat 211 million liters of radioactive liquid waste stored in at the site’s underground tanks.

But a budget proposal from the Trump administration threatens to cut cleanup by as much as $120 million, according to the Associated Press.