Monitoring under the Plutonium Management and Disposition Agreement : the prospects of antineutrino detection as an IAEA verification metric for the disposition of weapons-grade plutonium in the United States

Abstract

After the end of World War II, the world entered an even more turbulent period as it faced the beginnings of the Cold War, during which the prospect of mutually assured destruction between the world's largest nuclear weapon states was ever-present, and often provoked tense confrontations. Although fears of a nuclear holocaust significantly subsided after the dissolution of the Soviet Union in 1991, the world faced a potentially more dangerous prospect: the proliferation risks associated with the insecurity and unauthorized acquisition of Soviet-era nuclear warheads. Although all Soviet-era weapons were eventually acquired by Russia, concerns about the excessively large weapons stockpiles of the United States and Russia, combined with the goal of nuclear disarmament, led to the Plutonium Management and Disposition Agreement (PMDA). During the Cold War, the US and the Soviet Union respectively produced approximately 100 and 150 metric tons of weapons-grade plutonium (WGPu). Under the terms of the PMDA, both nations formally each agreed to irradiate 34 MT of excess military plutonium in the form of mixed oxide fuel (MOX) in nuclear power reactors. One of the major issues of concern associated with this agreement relates to the verification measures that will be implemented to ensure actual WGPu disposition. Additionally, despite a commitment (Article VII.3 of the PMDA) to engage and consult with the International Atomic Energy Agency (IAEA) to establish arrangements to monitor its plutonium disposition process, a formalized IAEA role within a potential multilateral verification regime has yet to be determined. In this work, the ability of the US to achieve the goals of its plutonium disposition campaign by 2018 is assessed. The suitability of the IAEA as an objective party to a multilateral verification regime under the auspices of the PMDA is also analyzed. In an attempt to aid the IAEA with such expected verification procedures, the applicability of antineutrino detection as a potential monitoring technology which could significantly enhance current monitoring procedures is considered. Although there has not yet been a formal demonstration of this technology under the auspices of the PMDA, the technology has been successfully fielded and nonintrusively operated at US and Russian reactors for years at a time, with the explicit aim of demonstrating potential relevance to a range of safeguards and verification tasks. The sensitivity of an antineutrino detector to antineutrino count rate measurements was analyzed through a hypothesis testing procedure which sought to identify statistically significant differences between the count rate evolutions of a designated baseline and potential diversion scenarios. With a specified set of parameters, the test demonstrated that the detector was capable of identifying the replacement of 7 WGPu MOX fuel assemblies with conventional LEU fuel assemblies within 360 days of the fuel cycle operation at a >95% true positive rate and a 5% false positive rate limit. These results were essentially still maintained even with a nonreactor- based antineutrino event background signal as high as 25%. Although pitfalls with regard to systematic uncertainty and operator malfeasance were revealed, potential solutions to such issues are also presented and discussed. All in all, the results obtained in this work confirm the potential efficacy and viability of antineutrino rate based measurements for a range of reactor safeguards and verification tasks.