How high is the proliferation risk associated with reactor grade plutonium? I was under the impression that Pu-239 contaminated with too much Pu-240 and Pu-241 could not be practically used to produce nuclear weapons. I attended a nuclear issues talk which claimed that reactor grade fuel COULD be used to make nuclear weapons... I've spoken with people who claim that reactor grade plutonium can't be used because it is too radioactive. The higher isotopes of Pu cause too much spontaneous fission and heat which make it both difficult to manufacture and implode. Does anyone know of any reliable papers which discuss this? Most of what I've found makes claims but doesn't reference any papers which are accessible. I'd like to better understand the risk of stored reactor waste. Could it be made 'safe' with long burn ups resulting in lower grade Pu?