Disposition of plutonium in Waste Isolation Pilot Plant (WIPP)

As part of its plutonium disposition program, the United States has been sending some material to the Waste Isolation Pilot Plant (WIPP) near Carlsbad, New Mexico. The repository, which opened in 1999, suspended operations after an accident in February 2014. During that time, WIPP accepted about 5.7 MT of plutonium in various forms. The graph and the table below provide data on the amount of plutonium emplaced in WIPP in 1999-2014. The table is based on the official information that the Department of Energy released to researchers.

The data shows that most of the plutonium emplaced in WIPP is weapon-grade material with Pu-239 content above 92 percent. Until 2003, the plutonium sent to WIPP has Pu-239 content of 94 percent. Also, the data shows that WIPP accepted about 28 kg of Pu-238, most of it starting in 2005.

The amount of disposed plutonium as reported by WIPP is different from the amount that the United States includes in its INFICR/549 reports to the IAEA. Information about plutonium disposition first included in the 2011 report, which stated that as of the end of 2010 "4.4 metric tons that has been disposed to waste after termination of safeguards post-1998." That material was part of the "61.5 metric tons of government owned plutonium that the United States has declared as excess to national security needs." The WIPP records show that at that point the facility accepted 5.06 MT of plutonium. Later, the United States reported that as of December 31, 2012 the amount of excess plutonium disposed of as waste was 4.5 MT. This number has not changed since. At the same time, the amount emplaced in WIPP was 5.5 MT at the end of 2012 and increased to 5.7 MT in 2014. The nature of the discrepancy is not clear. It is possible that it can be explained by the fact that WIPP accepted material that was excluded from the material accounting prior to 1994 and therefore is not counted as excess plutonium.