Demilitarizing Weapon-Grade Plutonium: Part II

Controversy About Proliferation Risk

Alexander DeVolpi

In Part I of this review about plutonium, various proven technical and institutional means for reducing nuclear proliferation were described. Enormous public value, in terms of nuclear-arms reduction and nonproliferation, can be derived from systematic demilitarization of fissile materials. Moreover, billions of taxpayer dollars can be recovered from commercial sales of materials no longer needed for weapons.

Nevertheless, unjustified and prolonged concern has been perpetuated about reactor-grade plutonium (RGPu). Much of the concern began with US government censorship of a 1962 nuclear-explosive test. Regarding its “nuclear yield,” the Department of Energy (DOE) has been evasive, simply asserting that “high-irradiation-level [RGPu] can be used to make nuclear weapons.”1 In 1994 DOE mentioned that the test yield had an upper limit of 20kt. In contrast, DOE has released much more substantive information about most other 1000 US nuclear explosions.

Some disturbing inferences about the still-limited data come to mind:2 (1) The material supplied might not have been “reactor grade,” but could have been more potent “fuel grade” or higher, and/or (2) The test yield and success might have been deliberately overstated by the government. This information management was evidently intended to avoid skepticism about the “successful” label attached to the 1962 test.

Specific questions were raised about the DOE assertions nine years ago in Physics & Society.3 The World Nuclear Association has stated that the test device had at least 85% Pu-239—a much higher fissile concentration than spent fuel from operating civilian reactors. Other nations have disagreed with the DOE “spin”: France, in particular, “scorned the US affirmation that it successfully exploded a weapon made with [RGPu]”4

DOE, by its own security criteria and practices, could have disclosed additional data. Abundant detail has been declassified for many US tests: For example, the 12 March 1968 “Buggy” series consisted of five simultaneous detonations using metallic HEU or weapon-grade plutonium (WGPu), with each explosive yield given as 1.08kt. Similar specifics have been released about numerous experiments going back to 1946.

The information still withheld by DOE can hardly add more proliferation value than data already divulged for other nuclear-explosive experiments. Moreover, the missing data would probably fortify awareness about inherent difficulties in weaponizing civilian plutonium, thus discouraging potential proliferators. It might even help formulate more cost-effective controls, without the need for relaxing nuclear-fuel-cycle safeguards.

In 1953 Britain conducted a test series (Operation Totem in Australia) using RGPu, reporting an 8-10kt explosive yield with relatively high fissile Pu-239 content estimated at 87-91%. The results were unacceptable: According to an official UK book (classified “Secret” in the US), the British never made weapons out of RGPu, even though they had lots of it.

For nearly a half century, controversy has lingered about RGPu. The implications affect civilian and military nuclear policy regarding arms control, demilitarization, international nonproliferation, and fuel management. Although the US government still implies nuclear weapons could be made from RGPu, that questionable posture has been documented only by ambiguous statements from the Atomic Energy Commission and its successors (ERDA, now DOE). Disagreeing are many experienced industry and laboratory nuclear physicists and engineers who recognize that impure plutonium has evidently not been incorporated in weapons for nuclear arsenals.

Statistical Limits and Nuclear Insights

DOE’s publicized declarations are not compliant with proper statistical characterizations of technical data. The agency has repeatedly asserted the 1962 test yield to be between zero and 20 kt. This implies a broad Gaussian (or Poisson) distribution with mean 10kt, and min/max between zero and 20kt. Absent additional information, almost any centrally-distributed FWHM could statistically match that meager data. However, warheads intended for a military arsenal are subject to unique standards: Neither expensive resources nor military effectiveness have evidently been squandered by the nine established nuclear-weapon states; their governments would not fabricate warheads with minimal yield and inconsistent military value.

The long-prevailing worldwide suspension in nuclear weaponization strongly refutes decades-old doom-and-gloom forecasts by individuals, such as Amory Lovins, Frank von Hippel, Ed Lyman, as well as by non-government organizations like the Union of Concerned Scientists—and even by a few prominent Americans once associated with the Manhattan Project. Vague terms, especially “weapons usable,” have often been deliberately exploited, and proper statistical boundaries are usually omitted. Too many forecasts depend almost entirely on existential threats of disaster. Tipoffs to such obfuscation are frequent mention of imprecise nouns, such as “capability” or “possibility,” and use of the vague term “weapons usable.”

Thousands of professional engineers and physicists in hundreds of nations have embraced nuclear power. Nuclear has had the best safety record of any major industry, irrespective of poor decisions and management at Chernobyl and in Japan. As indicated in the movie Pandora's Box, some prominent environmentalists have come to recognize benefits offered by nuclear power, especially the absence of air/ground/water pollution from particulates, ozone, aerosols, and CO2.

When President Jimmy Carter banned reprocessing of spent fuel, it was without French or British support. His decision had a politicized tone, and it’s doubtful that it reduced international momentum for reprocessing. More than 1700 tons of civil plutonium have now been produced worldwide, much of it for recycle in reactors. MOX now comprises almost 5% of nuclear fuel in power reactors. It also provides a path for converting WGPu (from military sources) into commercial electricity.

Despite equivocations by former US weapon designers—such as Ted Taylor, Bob Selden, and Carson Mark—the military-arsenal requirement for high fissile fraction has been frequently reaffirmed. Mark told me directly that “You can't design around predetonation.” Public literature advises that an arsenal-quality weapon requires small critical mass and low spontaneous-fission rate. That’s also been acknowledged explicitly or implicitly by other weapon states: Arsenal-qualified weapons utilize only isotopically high-grade materials. As pointed out by a highly experienced former DOE Assistant Secretary, a “credible nuclear deterrent must have reliable, deliverable WEAPONS that can be stored safely and are ready to use.”5 Individuals or organizations who invoke the vague term “weapon-usable” instead of “weapon-grade” are being deliberately ambiguous.

Professional engineers and scientists in worldwide civilian or naval nuclear programs (or test and training reactors) routinely apply their nuclear experience and calculations to prevent accidental criticality, that is, to preclude explosive yields. Government and industrial installations have become highly proficient at understanding energy releases from super-critical masses.

During the highly publicized Progressive Case, around 1980, some secrets about nuclear weapons were deliberately or inadvertently placed in the public domain.6 In addition, DOE officials pursued actions that drew attention to (or led to) disclosure of government-classified nuclear information regarding nuclear weapons and their design. Later, a detailed document was circulated about an unconsummated secret Swedish weaponization program that utilized only weapon-grade fissile materials.

In short, nuclear-weapons states have evidently based their projects on indigenous work and espionage, not on inferior materials. During World War II, Soviet scientists inferred the secret Manhattan Project’s purpose, citing an analogy “the dogs that didn’t bark.” Because of the sudden wartime lapse in Western nuclear physics and engineering publications, the analogy made sense. But now, with globalized information, it’s increasing difficult for any nation to clandestinely develop nuclear weapons without causing “dogs” to bark.

Nuclear Explosives and Proliferation

DOE has repeatedly asserted that “Virtually any combination of plutonium isotopes ... can be used to make a nuclear weapon.” Nevertheless, during WGPu production, deleterious Pu-238 and Pu-240 isotopes unavoidably accumulate, causing self-generated heat and neutrons. Without careful design and management, premature initiation would substantially reduce the potential explosive yield. Other complications can also be caused by excessive radiation and heat. Even so, a comparatively small (1kt) explosion would inflict terrible destruction within a radius roughly one-third of the Hiroshima zone. Indeed, a proliferating state or subnational group might theoretically be capable of inducing a destructive RGPu nuclear detonation using first-generation designs, materials, and technologies. But no weapon state has evidently introduced such unreliable devices into their arsenals.

Plutonium alone cannot be used in the simplest nuclear-weapon design (“gun type”): Potential proliferators with limited access to sophisticated technology would find enriched uranium to be a better choice than reactor plutonium. Either material can be used in a more sophisticated “implosion-type” device. In any event, according to former US weapons designers,7 Achieving “the size and weight of a modern weapon while maintaining performance and confidence ... would require one or more full-scale nuclear tests....”

Nations have thus invested in WGPu rather than RGPu. For example, in the 1980s the US considered spending billions of dollars on a special isotope-separation facility to enrich RGPu; that funding magnitude attests to the disutility of low-quality plutonium. Another obstacle is increased complexity (in weapons design, fabrication, and deployment). It’s highly unlikely that a rogue state or a sub-national group would be able to improvise an explosive using RGPu.

North Korea is the most recent nuclear-weapon state. Defying its NPT obligations, they probably produced WGPu in a “research” reactor. Uranium-enrichment facilities were also built. Beginning 2006, underground nuclear explosions in North Korea have been detected by international networks.

Iran in 1957 entered into an Atoms-for-Peace agreement with the US. Nearly a half-century later, Iran’s uranium-enrichment facilities became subject to an IAEA inquiry that uncovered violations of NPT safeguards. The IAEA concluded in November 2011 that Iran likely had undertaken research and experiments geared to developing nuclear-weapon capability. Since then, comprehensive multilateral negotiations have been underway for an international inspection regime that would closely monitor agreed limits on Iran’s nuclear program.

Iraq’s only “research” reactor was destroyed in 1981 by an Israeli air strike just before fuel was loaded. Consequently, Iraq went underground with electromagnetic isotope separation of indigenous uranium. When war broke out in 1990, just a few separators had been installed, but clearly Iraq had violated NPT obligations. Subsequently its nuclear capacity was rendered harmless.

Israel’s nuclear weaponization has chronically distorted international nonproliferation policy. Never having joined the international nonproliferation regime, Israel has apparently manufactured nuclear weapons with either passive or active support from other nations. WGPu could have been produced in their Dimona “research” reactor, which has never been opened to outsiders or to the IAEA.

Pakistan, a fairly recent nuclear-weapon state, has tested long-range missiles. Its neighbor, India, has for many years had a vast indigenous program for nuclear power and weapons. Both nations have remained outside of international safeguards.

A book-length technical evaluation of safeguards and nonproliferation has been written by a retired leading scientist of the Karlsruhe Nuclear Research Center.8 Also, a Russian group has conducted a thorough analysis.9 Dr. Kessler’s assessment shows that RGPu nuclear-explosive devices would be impaired by the high temperatures resulting from self-generated alpha decay and spontaneous fission. Kessler determined limits above which hypothetical nuclear weapons are not feasible on technical grounds, concluding that light-water-reactor plutonium with a burnup of 35 to 58 GWd/t cannot be used for making nuclear weapons. (Today’s light-water reactors attain fuel consumption in excess of 50 GWd/t.)

Conflictive nonscientific views about plutonium weaponization have been publicized with publications and presentations that lack statistical boundaries. Such indifference to appropriate methodology weakens credibility. For example, Amory Lovins' heralded 1980 predictions about (1) nuclear-power’s demise, (2) weapon-proliferation tendency, and (3) plutonium-demilitarization ineffectiveness are notably unfulfilled. Thirty-five years have passed since Nature and Foreign Affairs published his predictions, but those journals haven’t felt obliged to print long-overdue corrections.10

Closing Remarks

Nuclear proliferation has significantly slowed down—now much less than alarmists had predicted. Nearly a century has passed since the nuclear genie emerged—half a century since Nazi Germany and the US government became interested in uranium fission. The first critical reactor and first nuclear bombings occurred in the mid-1940s. The radiation age dates back longer.11 Radiation hazards and proliferation potential are now better understood and significantly diminished.

Meanwhile, the world suffered frequent and consequential non-nuclear calamities: dams breached, mines caved in, air pollution increased, bridges collapsed, fuel-tank cars exploded, world and regional wars fought, infectious outbreaks spread, and humans starved.12

Thus, the perspective of time and context now validates some favorable observations, supported by preponderant evidence. No more than three or four dozen individuals have verifiably died in connection with civilian nuclear-power accidents. Mortality from conventional power sources (such as hydro, coal, and gas) far exceeds that of nuclear electricity. Meantime, reactors and nuclear controls have benefitted from a safety-conscious culture and from first-class weapon-design facilities.

Fissile materials, when rendered unsuitable for potential military use, can indeed be considered demilitarized. Demilitarization lastingly diminishes the risk of nuclear-weapon proliferation and any danger that sub-national groups or individuals might make nuclear explosives. Exaggeration of nuclear-proliferation risk is simply not justified.

Sensible and responsible nuclear policies include the extraction of usable energy and the reduction of waste: At least six nations have commercialized excess MOX, thus minimizing public expenditures, effectively turning “swords into plowshares.” Uranium and plutonium demilitarization employ rather straightforward technologies with little technical risk. (Incidentally, destroying US chemical weapons is estimated to cost ~$35B—comparable to demilitarization of all nuclear-weapons.) As pointed out years ago, nuclear recycling is not going away; the choice now is simple: manage it poorly, or manage it carefully and safely.13

During the Cold War, more than 100,000 nuclear warheads were manufactured; the US recently disclosed that it still has 4,717 stockpiled weapons. Warhead demilitarization continues to be necessary and optimal for future arms control and nonproliferation, while recovering many billions of dollars in “sunk costs.”

Alexander DeVolpi, retired reactor physicist from Argonne National Laboratory, Fellow APS. He has conducted professional research, calculations, and experiments related to critical nuclear materials.


1. “Nonproliferation and Arms Control Assessment of Weapons-Usable Fissile Material Storage and Excess Plutonium Disposition Alternatives,” U.S. Department of Energy report DOE NN-0007 (Jan. 1977). “Additional Information Concerning Underground Nuclear Weapon Test of Reactor-Grade Plutonium”, U.S. DOE publication DOE FACTS, pp. 186-190 (August 1994); “Technical Summary Report for Surplus Weapons-Usable Plutonium Disposition,” Office of Fissile Materials Disposition, US Department of Energy (October 31, 1996)

2. A. DeVolpi, “Denaturing Fissile Materials,” Progr. in Nucl. Energy, 10:161 (1982); B. Pellaud, “Proliferation Aspects of Plutonium Recycling,” J. Nuclear. Matls. Mgt, 31:(1) 30-38 (2002); A. DeVolpi, "Fissile Materials and Nuclear Weapons Proliferation," Annual Reviews of Nucl. and Particle Science 36, 81-114 (1986).

3. G.E. Marsh and G.S. Stanford, “Bombs, Reprocessing, and Reactor Grade Plutonium,” Forum on Physics and Society, Vol. 35, No. 2 (April 2006).

4. Nuclear Fuel: 21 (8) (8 April 1996).

5. A.D. Rossin, “Secrecy and Misguided Policy,” Global 2001 Conf., Paris, France (11 Sep. 2001).

6. A. DeVolpi, et al., Born Secret: The H-Bomb, the Progressive Case and National Security, Pergamon (1981).

7. J. Carson Mark, "Explosive Properties of Reactor-Grade Plutonium," Science and Global Security, 4, 111-128 (1993); Robert W. Selden, “Reactor Plutonium and Nuclear Explosives,” (November 1976); “Can Terrorists Build Nuclear Weapons?,

8. G. Kessler, Proliferation-Proof Uranium/Plutonium Nuclear Fuel Cycles: Safeguards and Nonproliferation, KIT Scientific Publishing (2011).

9. E.F. Kryuchkov, et al, “Isotopic Uranium and Plutonium Denaturing as an Effective Method for Nuclear Fuel Proliferation Protection in Open and Closed Fuel Cycles,” (2011).

10. E.g., Amory B. Lovins, L. Hunter Lovins, and Leonard Ross, “Nuclear Power and Nuclear Bombs” Foreign Affairs (summer 1980).

11. Richard Rhodes, The Making of the Atomic Bomb (Simon and Schuster, 1986).

12. Bernard Cohen, Wikipedia (

13. Marsh and Stanford, op cit.

These contributions have not been peer-refereed. They represent solely the view(s) of the author(s) and not necessarily the view of APS.