Some operations at Los Alamos National Laboratory's Plutonium Facility have been put on hold after the National Nuclear Security Administration identified safety concerns.

A memo from Defense Nuclear Facilities Safety Board site representatives BP Broderick and RT Davis to DNFSB Technical Director TJ Dwyer states that one type of plutonium-purification process is suspended pending review of important safety controls. The safety standards in question are designed to prevent accidental nuclear reactions. The memo questions whether plutonium-bearing solutions are being stored in a tank outside the area where such substances are permitted.

"This situation presents both safety basis and criticality safety concerns," the memo reads, urging LANL to "take immediate action."

NNSA spokeswoman Toni Chiri says no plutonium actually entered the tank outside the facility; the issue is that it could. The tank in question won't be used again until LANL develops specialized valves to prevent plutonium from getting into it, Chiri says.

LANL activities are already facing scrutiny after NNSA's recent approval of an environmental assessment of a planned plutonium-processing facility, the Chemistry and Metallurgy Research Replacement facility.

The DNFSB memo also identifies "opportunities for improvement" in emergency operations after a small fire on LANL property this summer.