During the Cold War, the United States produced about 90 tonnes of weapons grade plutonium, which is 90,000 kg. A “significant quantity” of plutonium, per the parlance of the IAEA, is 8 kg, making the U.S. equipped with enough material for 11,240 Nagasaki-sized weapons. In 2000 the government, realizing this quantity to be a bit excessive, announced that it had 50 surplus tonnes of plutonium, and made an agreement with the Russian government to dispose of the surplus. This agreement, formally termed the Plutonium Management and Disposition Agreement, established plans for both weapons nations to dispose of 34 tonnes of weapons-grade plutonium.
The U.S. took definitive steps towards fulfilling this obligation last week, when the Tennessee Valley Authority (TVA) signed an agreement with the National Nuclear Security Administration (NNSA) to study the use of mixed oxide fuel (MOX) in five of its light water reactors (LWRs). MOX fuel is composed of uranium and plutonium and offers a higher burnup than traditional uranium oxide material. In the near term, the TVA will partially load its cores with MOX fuel, which will require no significant reactor modifications. An LWR core can be loaded with up to 50% MOX without requiring appreciable design modifications, though concentrations above 50% require core and facility adaptations due to the higher energy density and different neutronics of plutonium. In addition to burning MOX fuel in the pre-existing LWRs, the TVA has agreed to work on core designs and make environmental and reactor assessments for a next generation PWR that will run on 100% MOX. The fuel for this reactor will be fabricated at the MOX Fuel Fabrication Facility, located on the DOE’s Savannah River Site. Construction of this facility is expected to be completed in 2017, and the it should go online shortly thereafter.
The use of MOX in LWRs is a well-established technology, as it has already been implemented in 30 reactors across Europe. France is the world’s lead user of MOX fuel, contributing to France’s impressive nuclear electricity generation, which accounts for 78% of the nation’s total electricity generation. For French reactors, the plutonium for MOX fuel is obtained by reprocessing spent fuel, which contains about 1% plutonium. 96% of spent fuel is uranium, which can also be reprocessed and recycled. If both the plutonium and uranium are recycled from spent fuel, there is a 22% increase in the energy derived from the original uranium. In addition to increasing uranium utilization, reprocessing spent fuel into MOX has the added benefit of greatly reducing the waste burden of spent fuel. Seven LWR assemblies are required to produce one MOX assembly, resulting in a significant reduction in the volume, activity and toxicity of the waste. MOX fuel can also be produced using depleted uranium, which is a waste product of enrichment plants, rather than reprocessed uranium.
The 2000 plutonium disposition agreement between Russia and the U.S. marks a critical step towards disarmament, a treaty obligation that the two nations have long ignored. Under the Nuclear Nonproliferation Treaty, five nations are designated as Nuclear Weapons States, including the U.S. and Russia. Article VI of the treaty requires that these states make a “good faith” effort to disarm, an effort that has hitherto been underwhelming. Disarmament gained unprecedented governmental support last year, when newly elected President Obama’s surprisingly aggressive disarmament rhetoric raised eyebrows around the world. His clear statement that, “America seeks a world in which there are no nuclear weapons,” initiated a fresh round of disarmament dialogue, and it seems has finally spurred some action.
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