BOISE, Idaho — The U.S. Department of Energy says it’s concerned about a radiation leak two years ago at an eastern Idaho nuclear facility that contaminated nine workers, but the agency says it will not begin a formal investigation.

The federal agency’s Office of Enforcement in a letter dated Wednesday told Battelle Energy Alliance, a research contractor, that it would continue to monitor the company’s efforts to improve nuclear safety at the Idaho National Laboratory but no additional requirements were being imposed.

“The actual nuclear safety consequences of this event were low, but DOE views seriously any event in which workers receive unplanned radiological uptakes,” the letter states.

Officials say the low-level exposure of the nine workers in late August 2014 occurred after faulty air monitors failed to detect a release of radioactive material from a sealed compartment.

Battelle in a statement said it has taken corrective actions to address the federal agency’s concerns at the Idaho National Laboratory. “The safety of our workforce and the public is INL’s top priority,” spokeswoman Misty Benjamin said.

The exposure took place at the lab’s high-security Materials and Fuel Complex west of Idaho Falls at levels well below annual regulatory limits, according to a report prepared for the Energy Department and released in March.

To safely handle radioactive materials, workers put their arms into gloves mounted on the sides of sealed transparent boxes. The release occurred in one of two rooms with the glove boxes from Aug. 26 to Aug. 28, with an additional smaller leak on Sept. 3, the report said.

A radioactive material called americium escaped through several small holes later discovered in the glove-box equipment, the document said. Air monitor alarms that are supposed to alert workers didn’t detect the americium. A routine test of air monitor filters on Sept. 24 found the americium, leading to an evacuation.

“DOE considers this event to be a preventable nuclear safety matter, and it is the Department’s expectation that (Battelle) will fully implement the corrective actions needed to prevent recurrence,” the DOE wrote in the formal letter, called an Enforcement Letter, and that signals the agency’s decision not to pursue additional enforcement activity.

Officials say the leaks have been fixed and alert systems improved. The room and equipment where the leaks occurred returned to normal operations in January.