The Academy's study chairperson, John Holdren, clarified why they recommended that military plutonium be transformed into less easily reused forms. He explained that immobilization has the "disadvantage of not changing the weapon plutonium isotopically"-something that a reactor does. Such burnup (of mixed plutonium-uranium oxide-MOX) changes the isotopic components, making the plutonium far less suitable for weapons.

The Academy's review concluded that there were "nonproliferation liabilities" in not moving ahead with "imposing some built-in [isotopic] barriers to the reuse of military plutonium." Such isotopic barriers were the reason why Cold War nuclear arsenals were not made from low-grade materials. MOX burnup irreversibly demilitarizes weapons plutonium.

Holdren candidly acknowledges that "those who know my history know that I did not reach these positions because of lack of concern about proliferation or any history of understatement of the proliferation dangers of plutonium recycle."

Miller and von Hippel admit that "immobilized plutonium would be recoverable for reuse," conceding the potential "breakout advantage" from immobilization. So why are they advocating immobilization? Evidently they believe proliferation risks stemming from untreated civil plutonium to be more dangerous than the nuclear breakout potential from recoverable weapons plutonium.

Despite the claims of professors Miller and von Hippel that "a more sophisticated...argument has recently surfaced," the comparative benefits of irreversible isotopic demilitarization were recognized decades ago [3].

Their persistent labeling of plutonium as "weapons usable"-an imprecise and ambiguous term-obscures the crucial fact that its isotopic quality significantly affects a weapon's yield, reliability, complexity, and ease of manufacture. As evidence, one need look no further than the lengths to which weapons' developers have gone, without exception, to get high-grade plutonium.

Isotopic quality is meaningful because there are easier routes than reactor-grade plutonium for making nuclear weapons. One direct and feasible way would be to recover and reprocess the weapons plutonium that Miller and von Hippel want to store underground in a nationally accessible vitrified form.

Pending a more permanent solution, isotopic spoiling by MOX burnup has the desired demilitarization effect. It shunts would-be proliferators to more difficult sources of fissile materials. If-instead of relying on vested interests like "U.S. weapons experts" for their guidance-Miller and von Hippel more carefully studied published applied-physics calculations, they might better understand the reasoning of their peers at the National Academy who recognize the inherent disutility of poor plutonium grades.

Because of many problems with the immobilization-only option, the Academy proposed a "dual-track" approach for weapons plutonium: pursue development of both vitrification (immobilization) and reactor burnup. And, as Holdren reminds us, "There would be no reprocessing of spent fuel" in the MOX-burnup track.

Nevertheless, crusaders against nuclear reprocessing are more concerned about hypothetical dangers they perceive from civilian reactors than the more realistic dangers from materials now being removed from nearly 50,000 nuclear warheads. Still in service are another 36,000 weapons containing pristine nuclear material.

Blinded by their stance against nuclear reprocessing, such crusaders do not agree that destruction of weapon-grade materials should be the major arms-control goal. Weapons-grade plutonium is a proven commodity that aided nations in reaching the brink of mutual annihilation. The risks of proliferation from low-grade materials has been demonstrably more manageable. If the immobilization advice of Miller and von Hippel were pursued, scarce resources would be wasted and precious time would be unrecoverably lost.

Although nearly any form of plutonium or uranium can be rendered into a destructive or threatening device, our main concern should be a legacy of high-grade nuclear materials produced for military use by defense complexes. Retaining the material in the ideal isotopic form for weapons seems contrary to national security when we have the means to render it practically useless for nuclear war-fighting.

Miller and von Hippel, who use the term "obdurateness" when characterizing the positions of others, underrate the advantages of moving expeditiously towards irreversible isotopic demilitarization of weapons-plutonium stockpiles. It seems quite inconsistent of them to advocate storing weapons plutonium in a form that would probably be easier to reprocess than spent reactor fuel.

They should consider a compromise: immobilizing spent reactor fuel while irradiating weapons plutonium in reactors. Because the professors consider reactor-grade to be "weapons-usable," immobilization of spent fuel would meet their concerns. However, arms-control advocates prefer weapons-grade plutonium to get the irreversible treatment: isotopic demilitarization in a reactor.

Focusing the dual track-vitrification of spent fuel and burnup of weapons plutonium-would be a wise compromise and better use of resources.

[1] Marvin Miller and Frank von Hippel, "Let's reprocess the MOX plan," The Bulletin of the Atomic Scientists (July/August 1997).

[2] John P. Holdren, "Work with Russia", The Bulletin of the Atomic Scientists (March/April 1997).

[3] E.g., A. DeVolpi, Proliferation, Plutonium and Policy: Institutional and Technological Impediments to Nuclear Weapons Propagation, Pergamon (1979).