The U.S. Department of Energy indicated Friday that waste from a nuclear weapons laboratory stored in an underground dump in New Mexico might be the source of a major radiation leak that had exposed 21 people and closed the repository for months. The Energy Department said in a statement Friday that crews in their recent trip to the Waste Isolation Pilot Plant in southeastern New Mexico uncovered the disintegration of several heavy bags containing magnesium oxide. The bags sit atop several sealed drums containing nuclear waste from Los Alamos National Laboratory, a leading nuclear weapons manufacturer of the country. "The team is looking at the possibility that a chemical reaction may have occurred within a drum, causing a potential release," the department said in the statement. Investigators were also looking at whether the cause could be related to the waste packages themselves. The department said earlier it was not clear what damaged the bags. And the crews had not found any structural damage in the waste storage area of the repository. Officials said a possible cause of the problem might be the presence of untreated nitrate salts in some of the containers, which could result in an "energetic chemical reaction" if they came in contact with certain other material in the containers. Shipment of the waste in question from the laboratory to a temporary storage dump in Texas had been halted. Los Alamos National Laboratory had been forced to relocate its nuclear refuse to the Texas dump after a radiation leak shuttered the New Mexico dump on Feb. 14. Last week, the Energy Department released its preliminary findings of the radiation leak, 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 standards for a nuclear facility. The Waste Isolation Pilot Plant 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.