米露のPu処分における核不拡散、核セキュリティについての検討

Research on plutonium disposition by U.S. and Russia from the nonproliferation and nuclear security perspectives

小鍛治 理紗; 須田 一則 ; 玉井 広史 ; 田崎 真樹子 ; 清水 亮 

Kokaji, Lisa; Suda, Kazunori; Tamai, Hiroshi; Tazaki, Makiko; Shimizu, Ryo

冷戦後、米国とロシアはSTART条約等で核弾頭削減を実施してきた。2000年には一連の取組の結果として発生する余剰Puを34トンずつ処分する協定(PMDA)を締結している。近年、米国ではMOX燃料製造施設建設のコスト高のため、代替処分方法も検討している。改定PMDAでは兵器級Puを「Pu240/Pu239が0.10以下のもの」と定義づけ、第7条等で「Pu処分に際して当事国に監視、査察を実施する権利と義務」があること、第8条では「INFCIRC225/Rev.4の勧告を考慮に入れ責任もって管理する」よう定める。改正PMDAが定める34トンのPuを処分するため米国では、高速炉における照射、MOX燃料に加工し軽水炉において照射, 固化, 希釈、およびディープボアホールでの処分が検討されており、本研究ではそれぞれについて核不拡散、核セキュリティがどのように確保されているか検討を行った。

After the Cold War, the United States and Russia have been decreasing the number of nuclear warheads under the Strategic Arms Reduction Treaty and other agreements, with step-by step removal from nuclear military programs under the process of nuclear disarmament. In 2000, the two states signed the Plutonium Management and Disposition Agreement (PMDA), which prescribes each of them to dispose of at least 34 metric tons of plutonium. Recently, since the cost of constructing the Mixed Oxide (MOX) Fabrication Facility has increased significantly, the United States has been assessing alternatives. In the revised PMDA, which defines weapon-grade plutonium as "an isotopic ratio of plutonium 240 to plutonium 239 of no more than 0.10", Article VII states, "Each Party shall have the right to conduct and the obligation to receive and facilitate monitoring and inspection activities", and Article VIII prescribes, "Each Party shall be responsible...for...disposition plutonium...taking into account...INFCIRC/225/Rev.4...". In accordance with the revised PMDA's obligation to dispose of an excess of 34 metric tons of plutonium, irradiation in fast reactors, irradiation of MOX fuel in LWRs, immobilization, downblending, and deep borehole options have been considered by the United States. In this research, it is examined how these options could be implemented from the nuclear nonproliferation and nuclear security perspectives.