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 / Updated  / Source: Reuters

A nuclear waste storage site below New Mexico's desert is "in shutdown mode" after excessive radiation levels were detected, Department of Energy officials said Sunday.

An underground air-monitoring alarm went off at 11:30 p.m. local time Friday indicating unsafe concentrations of radiation inside the Waste Isolation Pilot Plant in what DOE officials said appeared to be the first such mishap since the facility opened in 1999. No workers have been exposed and there was no risk to public health, according to authorities.

Located in southeastern New Mexico near Carlsbad, the facility is designed as a repository for so-called transuranic waste, which includes discarded machinery, clothing and other materials contaminated with plutonium or other radioisotopes heavier than uranium.

The waste, shipped in from other DOE nuclear laboratories and weapons sites around the country, is buried in underground salt formations that gradually close in around the disposal casks and seal them from the outside world.

No workers were underground when the apparent radiation leak was detected in the vicinity of the plant's waste-disposal platform, and none of the 139 employees working above ground at the time was exposed, the DOE said.

As of Sunday, the source of the high radiation readings had yet to be determined, and a plan to send inspection teams below ground to investigate was put on hold as a precaution.

"We're in shutdown mode," DOE spokesman Bill Mackie said, adding that they are waiting for other assessments done before we authorize re-entry."

- Reuters