I am aware of Garwin’s theories. In his discussion when he talks about R-Pu, it does not appear that he is talking about the very high-burnup material produced by today’s LWRs with 18-24 month fuel cycles. I also see no mention of the spontaneous neutron contribution of the higher transuranics beyond Pu240.
His statement also relies heavily on J. Carson Mark, a brilliant bomb designer of the fifties and sixties. I believe that later in his life, perhaps regretting his substantial contributions to the technology of warfare, Mark overcompensated by providing data that exaggerated proliferation fears. I doubt one will find someone of Dr. Mark’s capabilities crouching in the foothills ofKandahar.
Then there is the confounding fact that, if it is so easy, and with tens of thousands of tons lying around for the taking, why has not one single weapon or test device has ever been constructed from “spent” LWR fuel?
Garwin gives a lot of figures and offers a lot of unproven statements as if they were certain – but “the proof is in the pudding”. I repeat, no explosive devices, let alone weaponizable bombs, have ever been built from LWR fuel. Unfortunately the excellent tutorial “Why You Can't Build a Bomb From Spent Fuel” seems to be offline. When it returns see http://depletedcranium.com/why-you-cant-build-a-bomb-from-spent-fuel .
If concern about R-Pu stockpiles persist, the best way to achieve permanent disposal would be fissioning it completely, and simultaneously generating massive quantities of electricity. I tend to suspect the motives of those who, on the one hand lament the presence of tons of R-Pu, but on the other hand oppose the development of the fast-spectrum reactors that are the best means of permanently eliminating these materials.
If terrorists obtain nuclear weapons, which is the current focus of many in the non-proliferation community, they will most likely be diverted from already-fabricated nation-state warheads. Reprocessed LWR spent fuel, because of the extraordinary difficulty - if not impossibility - of weaponizing it, is not where the focus of attention should be,
In fact this provides fodder for the anti-nuclear activists who would deny the essentiality of constructing next-generation reactors to extract energy from the existing Pu stockpiles and provide emissions-free electricity for a rapidly growing world population.