by this material. As long as this material remains in readily weapon-usable form, it will:

• continue to be vulnerable to theft (by parties other than the possessor state) and diversion (by the possessor state) for use in nuclear weapons (which we call the direct risks);

• send the signal that a reversal of current arms reductions remains possible, with negative consequences for arms reduction and nonproliferation efforts (the indirect risks).

The timing of disposition options is crucial to minimizing both types of risks. Minimizing the time until the start of operations to transform the surplus WPu into forms less easily used for weapons, and minimizing the time until this transformation is completed, are of obvious value in reducing the direct risks of theft and diversion. An expeditious approach reduces the indirect risks, moreover, by signaling commitment to irreversible arms reductions and seriousness in addressing proliferation hazards.

While the direct risks are significantly greater in the former Soviet Union, under current economic and political circumstances, than in the United States, the indirect risks apply equally to both countries. To reduce the risks in both categories, the two countries should proceed expeditiously, and more or less in parallel, with programs of WPu disposition that move beyond the status quo—guarded interim storage of plutonium "pits" in the form in which they emerge from weapon dismantlement—to make it significantly more difficult for this plutonium to be reused in weapons by the original possessor state or by others.

In considering the options for using irradiation in nuclear reactors or immobilization with reactor wastes to provide such barriers, the panel has addressed, on a comparative basis, technological readiness, institutional requirements, economics, and environment, safety, and health. We have given the greatest weight, however, to the security characteristics of the various options—their capacity to reduce rapidly the direct and indirect security risks posed by prolonged storage of the plutonium as pits, while minimizing any new security risks arising from the disposition options themselves. (The task of comparing those long-term disposition options within the panel's purview with other options, as well as the task of comparing all these options with indefinite storage, was left to the parent committee.)

The panel recommends that the goal for WPu disposition operations to be undertaken in the next few decades should be to meet what this panel and the parent committee call the "spent fuel standard." This means making the excess WPu roughly as inaccessible for weapons use as the much larger and growing