The crew inspecting an underground nuclear waste repository in the U.S. state of New Mexico have found what is suspected to be the source of a major radiation leak that contaminated 21 workers in February, U.S. media reported Thursday.

A team of crews found several "grossly disturbed" bags of minerals at an underground vault in the Waste Isolation Pilot Plant in southeastern New Mexico, local media KOB quoted officials with the U.S. Department of Energy as saying.

The minerals, called magnesium chloride, were placed on top of waste containers to absorb moisture and carbon dioxide. The officials didn't explain how the minerals were believed to be connected to the Feb. 14 radiation leak, which resulted in the facility being closed for six weeks.

Officials said it was not clear what damaged the bags, and that the crews had not found any structural damage in the waste storage area of the repository.

Last week, the Energy Department released its preliminary findings, citing poor management, ineffective maintenance and a lack of proper training and oversight at the plant. The federal department found much of the operation failed to meet the standards for a nuclear facility.

The underground dump stores "transuranic waste" leftover from nuclear weapons research and testing from the nation's past defense activities, according to the Energy Department's website. The waste includes clothing, tools, rags and other debris contaminated with radioactive elements, largely plutonium.