Nuclear power debate, Adelaide, Australia, 5 Feb 2010

"J. Carson Mark. Particularly unjustified has been selective “milking” of publications written by J. Carson Mark, who headed Los Alamos’ weapons-theory branch early in the Cold War. Some nonproliferation dogmatists have been exploiting his written words to support their otherwise unfounded alarmism.

       Mark wrote a paper, “Reactor-Grade Plutonium’s Explosive Properties,” a definitive description of the topic published in 1990 by the Nuclear Control Institute.[1] At the behest of the Department of Energy, a revised version, “Explosive Properties of Reactor-Grade Plutonium,” was published in a 1993 issue of Science and Global Security (Vol. 4, pp. 111-129), which includes an “Appendix: Probabilities of Different Yields” by Frank von Hippel and Edwin Lyman. [2]

       It is instructive to compare the 1990 and 1993 papers which are essentially the same except for a curious, but important difference: Missing from the 1993 version is Mark’s carefully defined term “weapon” as“an object suitable for a stockpile by a military organization.” No explanation for this obvious and crucial omission is supplied with the published revision. My personal interviews and conversations with Mark before 1993 confirmed the intended significance of his 1990 definition.

        While reprints of the 1993 paper designate J. Carson Mark as the sole author, the Princeton University website index for Science and Global Security credits the revised paper to “Mark, J.C., von Hippel, F.N., Lyman, E.” The revised version acknowledges that “This article is adapted from an earlier paper” (a reference back to Mark’s original 1990 article).

      Mark has often warned that plutonium of any grade (i.e., isotopic composition) could probably be incorporated into an explosive device by subnational groups to produce a fission yield of “some hundreds of tons.” But he also pointedly advised that a “military organization” (of an industrialized nation) would want warheads using fissile materials that result in a “reliable known yield” and “objects that could be turned out in production-line fashion.”

      Thus, civil plutonium certainly could not directly meet Mark’s weaponization criterion; it should not be loosely represented as “weapons usable.” Normative domestic and international safeguards would be sufficient (as well as obligatory) to keep civil plutonium from being used as a nuclear explosive by anyone.

      Those who bandy the vague term “weapons usable” are demonstrating their unfamiliarity with military specifications, which are explicit quality standards intended to assure predictable results with high confidence. National military organizations stipulate military-grade materials for reliable weapons, not materials that are simply “usable.”

De Volpi added, "Carson Mark calculated the range of fizzle yields to be expected from a Trinity-style device made with reactor–grade material (“Trinity” was the first test of an implosion-driven plutonium warhead, at Alamagordo, New Mexico, in 1945)."

For [reactor-grade plutonium], setting the spontaneous neutron emission rate at 20x10⁵ per second is equivalent to choosing the mass as 10 kg, since the spontaneous emission rate of reactor-grade plutonium is ~200 n/s/g. According to the curve, there will always be a yield ratio of at least 2.7%, and the probability of degradation to a yield ratio less than 0.1 is about 83%. This is why it is often said that likely fizzle yields range from 100 tons to a kiloton or so, for a Trinity type of device. This is also why reactor-grade plutonium must be safeguarded — it’s possible get an explosion with the stuff. Fortunately, the technical hurdles are daunting."

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 "Many problems related to the possible substitution of reactor plutonium in existing weapon designs have been publicly noted with most discussion usually limited to the problems of pre-initiation and heat generation. Other difficulties that affect reactor-grade bomb design and construction are described in Part 2: Controversy about Demilitarizing Plutonium.

      The original development of modern, efficient fission weapons required an extensive nuclear-testing program; any nation making such an effort will not waste its time and money on reactor-grade plutonium. It is far simpler to produce weapon-grade plutonium, as other nations — India, North Korea, and Israel — have evidently done.

      The terrorist threat from reactor-grade plutonium has been greatly exaggerated by the argument that what is theoretically possible to do can be done by subnational groups (See Part 2).

      It is transparently speculative, as done by nuclear-power opponents, to promote the notion that proliferation will increase if spent reactor fuel is reprocessed. Spent-fuel reprocessing securely consummates the nuclear fuel cycle, and it fosters a rational and conservative reactor-waste disposal policy."

http://knol.google.com/k/nuclear-weapons-proliferation-demilitarization-overview#

An explosion of reactor grade plutonium would not be more powerful than the explosion of a device made from $100,000s worth of high explosives.  In a well know paper, Amory Lovins suggested: 

]...It is therefore incorrect to state categorically that bombs made from reactor-grade or deliberately ‘denatured’ Pu are less effective, less powerful, or less reliable than those made from weapons-grade Pu."

De Volpi responded: "While Lovins convinced the editors and reviewers of Nature that a neophyte had figured out nuclear weaponry enough to become an publishable expert, his inverted conclusion is not supported by theoretical or anecdotal evidence.

http://knol.google.com/k/nuclear-expertise-the-amory-lovins-charade#

Since Mark is not an expert in nuclear disarmament issues, he does not have the status to challenge Alexander De Vopi on the weaponizability of reactor grade plutonium.