(a) Spent fuel and plutonium discharges through 1993 are calculated in David Albright, Frans Berkhout, and William Walker, Plutonium and Highly Enriched Uranium 1996, World Inventories, Capabilities and Policies (Oxford:Stockholm International Peace Research Institute and Oxford University Press, 1997). Spent fuel from 1994 through 1998 was calculated following the methodology detailed in Appendix B of Plutonium and Highly Enriched Uranium 1996. For spent fuel in LWRs we modified this method by subtracting 1/6th of a core of fuel from each reactor to compensate for uncertainty in the fuel unloading schedule. Plutonium from 1994 through 1998 was calculated following the methodology detailed in Appendix B of Plutonium and Highly Enriched Uranium 1996. The uncertainty in these estimates is 10 to 20%. An exception is the United States, which declared 274.4 tonnes of plutonium in spent fuel in 1996 and so the uncertainty in the US estimates is less than 10%. Additionally, Canada has declared its discharges of spent nuclear fuel, which corroborated these estimates. These estimates do not include reactor cores, which contain about 100 tonnes of plutonium. And, these estimates have not been corrected for the decay of plutonium 241 into americium 241, nor have they been corrected for plutonium inserted into reactors in the form of MOX fuel and subsequently fissioned. See Table A2.