The U.S.-Russian Joint Studies on Using Power Reactors to Disposition Surplus Weapons Plutonium as Spent Fuel

Abstract

In 1996, the United States and the Russian Federation completed an initial joint study of the candidate options for the disposition of surplus weapons plutonium in both countries The options included long-term storage, immobilization of the plutonium in glass or ceramic for geologic disposal, and the conversion of weapons plutonium to spent fuel in power reactors. For the latter option, the United States is only considering the use of existing light-water reactors (LWRs) with no new reactor construction or the use of Canadian deuterium-uranium (CANDU) heavy-water reactors. While Russia advocates building new reactors, the cost is high, and the continuing joint study of the Russian options is considering only the use of existing VVER-1000 LWRs in Russia, and possibly Ukraine, and the existing BN-600 fast-neutron reactor at the Beloyarsk Nuclear Power Plant in Russia. The use of Canadian CANDU reactors is also an option. Six of the seven existing VVER-1000 reactors in Russia and the eleven VVER-1000 reactors in Ukraine are all of recent vintage and can be converted to use partial MOX cores. These existing VVER-1000 reactors are capable of converting almost 300 kg of surplus weapons plutonium to spent fuel each year with minimum nuclear power plant modifications. Higher core loads may be achievable in future years. The BN-600 reactor, which currently uses enriched uranium fuel, is capable (with certain design modifications) of converting up to 1,300 Kg or 1.3 metric tons (MT) of surplus weapons plutonium to spent fuel each year. The steps needed to convert the BN-600 to a plutonium-burner core are:

• 1. Elimination of the depleted uranium breeding blankets and their replacement with a combination of a steel reflector and boronated shield;

• 2. Initial conversion to a hybrid enriched uranium-plutonium-fueled core sufficient to preserve a zero value for the sodium void reactivity effect; and

• 3. Ultimate conversion to the plutonium-burner core that requires several modifications to the fuel design and the reactor.

The step involving the hybrid core allows an early and timely start that takes advantage of the limited capacity for fabricating uranium-plutonium mixed oxide (MOX) fuel early in the disposition program. Finally, the design lifetime of the BN-600 must safely and reliably be extended by 10 years to at least 2020 so that a sufficient amount of plutonium (-20 MT) can be converted to spent fuel.