The 3-foot-tall H1616 shipping container was discovered in November when Mid-Carolina Steel & Recycling notified authorities of its presence.
"It wasn't contaminated, it didn't have anything in it and it turned out that it was damaged," said Will Callicott, the spokesman for Washington Savannah River Co., which manages the nuclear site.
The containers, which transport the gas used to boost the explosive power of nuclear weapons, are carefully inventoried when they have something in them, he said, but they are not as heavily monitored when empty.
Although the recycler routinely participates in the site's scrap metal program, no one has determined how the empty container was included in the material sent to Columbia.
The fact that a container normally protected by security programs left the site undetected drew criticism from Nuclear Watch South, an anti-nuclear group that issued a news release earlier this week.
"It is nothing short of amazing, especially given the heightened security environment in this country, that a tritium shipping container could go missing and not be noticed by DOE, " said Tom Clements, of Nuclear Watch South.