ALBUQUERQUE, N.M. Feb. 27, 2014

More analysis is needed to determine exactly how much radiation workers were exposed to during a recent leak at the nation's underground nuclear waste dump in southeastern New Mexico, officials said at a news conference Thursday.

Preliminary tests have found that 13 workers who were working above ground the night of the leak inhaled radioactive particles. Those results were announced Wednesday by the U.S. Department of Energy and the contractor that runs the Waste Isolation Pilot Project near Carlsbad.

At Thursday's news conference, officials emphasized that all radiation readings at the site have been at low levels, and it would be too soon to speculate about any potential health effects.

Officials haven't said exactly what the levels were in the area where the employees were working the night of Feb. 14, when an alert went off indicating a leak in the repository a half mile below. More tests are being ordered on the workers as well as some employees who were at the site the next day.

The accident is the first-known release of radiation since the dump near Carlsbad began taking plutonium-contaminated waste from the nation's nuclear bomb building sites 15 years ago. It came just nine days after a truck hauling salt in the plant's deep mines caught fire, but officials say they are confident the incidents are unrelated.

Officials said they can tell from their analyses of air samples in and around the plant that a container of waste leaked, but they haven't been able to get underground to find out what caused it.

The Energy Department has released detailed information from air monitors around the site, which back their assertions that releases off site were below those deemed unsafe.

And they have said that all indications are that a filtration system designed to immediately kick in when radiation is detected and keep 99.7 percent of contamination from being released above ground worked.

But the fact that the workers were exposed raises questions about those claims, according to Don Hancock, director of the Nuclear Waste Safety program at the Southwest Research and Information Center.

The dump's systems "are in the guinea pig stage," he said. "We know in theory what they were designed to do, but we don't know how well they worked because they have never been tried."

Farok Sharif, president of the Nuclear Waste Partnership, said during Thursday's news conference that he hopes to be able to send probes within a matter of days into the mines soon to get readings to determine when investigators can re-enter the repository.

The dump is the nation's first deep underground nuclear repository and the only facility in the country that can store plutonium-contaminated clothing and tools from Los Alamos National Laboratory and other federal nuclear sites.

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