During the last few months there have been a number of important policy decisions made that will have a direct impact on research programs related to the fate of plutonium and other actinides.
This past November, President George W. Bush proposed to reduce the number of deployed U.S. warheads from 6,000 to between 1,700 and 2,200 by 2012. Russian President Vladimir Putin responded with a pledge to reduce the Russian nuclear arsenal to 1,500 warheads.
The Department of Energy (DOE) subsequently announced that it will move forward with a plan to convert approximately 34 metric tons of "excess" weapons plutonium into a mixed oxide (MOX) fuel to be "burned" in commercial reactors.
An earlier, parallel program to immobilize a part of this plutonium-the so-called "scrap plutonium"-into a durable solid for storage and direct disposal has been abandoned. The parallel strategies were based on the concept of the "spent fuel standard" that envisioned the fissile material as being protected by highly radioactive fission products.
President Bush has recommended the Yucca Mountain site in Nevada for the geologic disposal of used nuclear fuel from nuclear power plants and high-level waste from defense programs. The MOX fuel, after a once-through cycle of burn-up, is destined for disposal in the Yucca Mountain repository.
Each of these policy decisions is controversial, and each is linked to the other through a complex chain of legal, regulatory, and political decisions. The failure of any single part of the policy chain will have a profound effect on the success or failure of the other policy decisions.
As an individual researcher, I have become increasingly concerned at the minimal role science plays in arriving at these decisions, and even more concerned that these decisions remain disconnected from one another. In this short piece, I cannot argue the merits or deficiencies of the individual policy decisions or describe their connections. I can, however, raise some simple issues that should be addressed in the formulation of these policies.
"Burning" the weapons-grade plutonium will not reduce, to any major extent, the inventory of plutonium. U.S. vulnerability to terrorist attack using diverted materials is not much reduced by the new policy. Although the isotopic vector of the plutonium will have been modified, the spent MOX fuel is still a potential source of weapons-usable material.
Protecting fissile material, either in the spent nuclear fuel or in a high-level nuclear waste glass, is only a short-term solution, as this strategy essentially protects a fissile nuclide with a half-life of 24,100 years with the high activity of fission products whose half-lives are on the order of 30 years.
Finally, MOX fuel, mainly UO2, is not stable under the oxidizing conditions that will prevail at Yucca Mountain. In presence of moisture and air, one can expect rapid alteration of the spent fuel and the formation of mobile UO22+ complexes. This spent MOX fuel increases the overall inventory of long-lived fissile material, and this may have an impact on the long-term safety of the repository.
As researchers, should we be concerned with these policy decisions? We could, perhaps, leave such considerations to higher-level government officials, but as Thomas Jefferson said, "Science is my passion; politics my duty." Because of changes in policy, research programs will begin and end abruptly.
In studies of the radiation-resistance of compositions in the Gd2 (ZrXTi1-x )2O7 binary, we discovered that ion beam irradiations could be used to create a buried layer of disordered fluorite-type structure in a matrix of pyrochlore. The disordered structure forms at the peak of the damage profile and has an ionic conductivity of two to three orders of magnitude greater than the surrounding insulating matrix. Thus, research on a potential plutonium-bearing waste form has also created a new avenue for the design and fabrication of nanoscale mixed ionic-electronic conductors in the pyrochlore oxides. This has important applications in the development of solid oxide fuel cells and sensors. (Physical Review Letters, 87, 2001).
New programs will be focused on supporting the present policy decision. Effort and expertise are lost with each change. Costs escalate as programs are redirected. Less time than money is usually available to develop supporting data, models, and a scientific rationale for a new policy.
I understand that change is necessary, as every new policy has specific scientific and technical needs, but these changes drive the science—rather than having science inform the policy.
I want to argue that, while abrupt changes may be the fate of applied research programs, this should not be the fate of basic research. A policy decision does not settle the fundamental scientific issues.
In fact, in my experience, there is little evidence that the fundamental limitations outlined by science are used to constrain the conceptual framework of the policy. Cost, schedule, and politics are more likely to be the drivers of policy than the underlying science. With faith and funding, every technical problem is presumed to have a solution.
However, most policy decisions in the nuclear domain have proven to be high risk, the cost is high, and failure propagates throughout the system. The high cost and extended delays in the construction and operation of the Defense Waste Processing Facility at Savannah River have impacted the efforts to build a similar vitrification facility at Hanford.
A recent directive from the Assistant Secretary for Environmental Management now promotes a goal of eliminating the need to vitrify at least 75 percent of the waste presently destined for vitrification.
The original decision to vitrify waste at Savannah River coincided with the decision to eliminate basic research on alternative waste forms. The decision to look at alternatives to vitrification at Hanford will now require considerable effort and research on alternative waste forms. With each swing of the pendulum, the cost increases.
Every policy decision should anticipate failure and explicitly develop alternatives. As a small example, I cite our own work on radiation effects in phases that can incorporate actinides.
Until recently, the U.S. strategy included the development of a titanate pyrochlore for the immobilization of the "scrap" plutonium (to be surrounded by a high-level waste glass in a canister, the "can-in-can" concept).
Although durable, the titanate pyrochlore is highly susceptible to alpha-decay damage, becoming fully amorphous in hundreds of years. However, through a basic research program funded by Basic Energy Sciences, our research group discovered that the closely related zirconate pyrochlore is resistant to radiation damage, remaining crystalline for millions of years.
From a scientific perspective, this phenomenon is of fundamental interest and is the subject of exciting research at Los Alamos and Pacific Northwest National Laboratory in Washington, as well as in France, England, and Russia. From a policy perspective, the discovery is irrelevant, as immobilization of plutonium in ceramics is not the present strategy. Still, this discovery provides an alternative to the present policy.
The discovery of a new class of radiation-resistant solids opens the door to research on a new class of materials that may have many applications to the materials problems throughout the DOE complex. As is often the case, there have already been important spinoffs from studies of the radiation damage effects in these materials because the ionic conductivity of Gd2(Zr, Ti)2O7 can be greatly increased by disordering the structure to a simpler fluorite structure. Ion-beam irradiations have been used to manipulate the conductivity of these solids at the nanoscale.
The structure of funding within DOE often places a high priority on research and engineering programs that support present policies. However, the risk of failure could be lowered if there were a conscious effort to fund basic research programs that provide future alternatives to today's policy.
This editorial was contributed by Rodney C. Ewing of the University of Michigan, departments of Nuclear Engineering and Radiological Sciences, Materials Science and Engineering, and Geological Sciences.
The opinions in this editorial are the author's. They do not necessarily represent the opinions of Los Alamos National Laboratory, the University of California, the department of Energy, or the U.S. government.
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