In a decree published today (PDF, English translation), President Putin of Russia suspended implementation of the Plutonium Management and Disposition Agreement (PDF) that was signed by the United States and Russia in April 2010. In the agreement, the two states made a commitment to eliminate 34 tons of weapon-grade plutonium each.
The decree justifies the suspension of the agreement by the "fundamental change of the circumstances, an emerging threat to strategic stability that resulted from unfriendly actions of the United States toward the Russian Federation" and the "inability" of the United States to fulfill its plutonium disposition obligations. Also, the decree refers to "the need to undertake urgent measures to protect security of the Russian Federation."
Importantly, the decree states that the plutonium that was to be eliminated under PMDA "is not used for the purposes of manufacturing nuclear weapons or other nuclear explosive devices, or for research, development, design, or tests that are related to such devices, or for any other military purposes."
The mechanism of suspending implementation of the agreement chosen by Russia is not entirely clear. The agreement itself does not seem to have a termination or withdrawal mechanism. The presidential decree refers to the Russian law on international treaties and suggests that the suspension will enter into force 120 days after the Russian government notifies the U.S. administration to suspend implementation of the agreement.
The United States has, indeed, encountered significant problems with implementing its original plutonium disposition plan. U.S. administration suspended construction of the MOX Fuel Fabrication Facility and plans to terminate it. This decision, supported by many experts, has met some resistance in Congress, where supporters of the U.S. MOX program pointed at Russia's concerns about the change of plans, publicly expressed by president Putin in April 2016, as a justification for continuing with the MOX route. The Obama administration and many U.S. experts were optimistic about the prospects of reaching an agreement with Russia that would accommodate any changes in the U.S. plutonium disposition program, but others were skeptical.
It is important to emphasize that Russia is likely to continue its plutonium disposition program that it created for the purposes of PMDA. However, it would be free not to implement certain elements of the agreement that deal with transparency and accountability.