Evolution Of Surplus Plutonium Management And Disposition Strategies In The United States

Several nations possess stockpiles of separated plutonium-239, principally resulting from the development of nuclear weapons, but also from reprocessing commercial spent nuclear fuel. The United States has declared about 50 metric tons of weapons-grade plutonium in various physiochemical forms as surplus. Much of this inventory (34 metric tons) is subject to a bi-lateral disposition agreement (the Plutonium Management and Disposition Agreement, PMDA) signed by the United States and the Russian Federation in 2000, when the initial paths for disposition in the United States were: (1) the generation of irradiated MOX fuel and (2) immobilization in high-level waste (HLW). In 2010 the PMDA was amended such that the United States indicated it would pursue only the irradiation of MOX fuel. Disposition was largely about rendering the plutonium unattractive and inaccessible (as irradiated MOX spent fuel) and was more muted on the issues of disposal, as its subsequent permanent isolation was expected to be in the national geologic repository at Yucca Mountain. Since 2010, the geopolitical and technical dynamic has shifted considerably, forcing the United States to adjust its plutonium disposition strategy. Such shifts include the termination of United States MOX fuel development, the cancellation of a deep borehole field test demonstration, uncertainty in the availability of Yucca Mountain or other repository, efforts to expand the Waste Isolation Pilot Plant volume disposal capacity, the potential for advanced reactors using plutonium fuels has risen, and the desire for renewed plutonium pit production has emerged. Most recently the Department of Energy has elected to pursue a multi-decade strategy of ‘dilute and dispose’ wherein weapons-grade plutonium is down-blended with an adulterant to ensure it “is not recoverable without extensive reprocessing” and disposed as transuranic waste in the Waste Isolation Pilot Plant. The dilute-and-dispose strategy faces new technical, regulatory, and geopolitical challenges. This paper will illuminate the challenging path of the U.S. plutonium disposition program, discussing the evolution of disposition strategies in light of shifting domestic and international geopolitical environments and changing technical influences. Insights from this review may be useful to those nations now beginning to contemplate their own objectives for surplus plutonium disposition.