Physics and Fuel Performance of Reactor Based Plutonium Disposition : Workshop Proceedings Paris France 28 30 September 1998 Following recent disarmament agreements the Russian Federation and the USA have declared part of their stockpiles of weapons grade plutonium as a surplus to their national defense needs. This material needs to be disposed of and one of the suggested means of doing so is burning it in existing reactors and transforming the material into spent fuel. The experience in these two countries with mixed oxide fuel (MOX) is either dated or scarce. Several European countries and Japan however have acquired much experience in using MOX fuel in reactors which was shared at this important workshop. This publication presents the workshop results which reviewed existing technical information from the civil nuclear power programmes that are beneficial to weapons grade plutonium disposition. It also proposes concrete actions that could help expedite this process in the near future.