The federal government says a 200-pound bundle of highly enriched uranium fell 15 feet from a crane into a vat of acid in August.
But employees failed to notify their superiors, according to a report by the Defense Nuclear Facilities Safety Board, and another accident happened a few days later.
A subsequent investigation found that caps on the uranium bundles had small protrusions that caused friction. That activity, in turn, caused the bundles to disengage from the crane.
The federal board says any safety risks from the accidents were small, but that such an accident had "potential safety criticality safety implications," meaning they could have possibly caused nuclear chain reactions. Those reactions could potentially expose workers to radiation.
Savannah River Site officials deny that the potential for a criticality existed.
Site officials have fired the workers.
The problems that led to the accidents have been fixed, they say.
The accidents happened during a process to convert the uranium into fuel for commercial nuclear reactors. The bundles were being lowered into what's called a dissolver, in which acid dissolves the uranium.
To read the Defense Nuclear Facilities Safety Board report on the matter from Aug. 14, click here.
To read the board's report from Aug. 21, click here.