Excess Fissile Materials Research Articles

Crystal chemistry of uranium (V) and plutonium (IV) in a titanate ceramic for disposition of surplus fissile material

We report X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine-structure (EXAFS) spectra for the plutonium LIII and uranium LIII edges in titanate pyrochlore ceramic. The titanate ceramics studied are of the type proposed to serve as a matrix for the immobilization of surplus fissile materials. The samples studied contain approximately 10 wt% fissile plutonium and 20 wt% natural uranium, and are representative of material within the planned production envelope. Based upon natural analogue models, it had been previously assumed that both uranium and plutonium would occupy the calcium site in the pyrochlore crystal structure. While the XANES and EXAFS signals from the plutonium LIII are consistent with this substitution into the calcium site within pyrochlore, the uranium XANES is characteristic of pentavalent uranium. Furthermore, the EXAFS signal from the uranium has a distinct oxygen coordination shell at 2.07 Å and a total oxygen coordination of about 6, which is inconsistent with the calcium site. These combined EXAFS and XANES results provide the first evidence of substantial pentavalent uranium in an octahedral site in pyrochlore. This may also explain the copious nucleation of rutile (TiO 2) precipitates commonly observed in these materials as uranium displaces titanium from the octahedral sites.

Status of the Pangea International Repository Feasibility Studies

ABSTRACTThe potential technical, scientific, safety, security, environmental and economic advantages of implementation of deep geologic repositories for the disposal of nuclear waste within an international framework were outlined in papers from the IAEA and from the Pangea organization over the past three years. Of increasing importance are the security and non-proliferation benefits which could result from having closely supervised centralized repositories for declared surplus fissile materials resulting from disarmament activities in nuclear weapon states.The Pangea concept is for repositories sited on technical and safety grounds independent of national boundaries. The sites would be in geologic formations situated in flat, stable, arid regions, where the convincing demonstration of long-term safety should be easier to achieve. Pangea identified several potential host regions of the world which warrant further investigation of their suitability for an international repository. As yet a formal feasibility study has been initiated only in Australia. This was allocated first priority due to the vastness of the region with potentially suitable geology, also because of its stable governmental system, its strong environmental record and non-proliferation credentials. Australia also has a strong anti-nuclear movement, no nuclear power plants, but an important uranium mining industry.Hence progress to date in Australia has been mixed. Political resistance has culminated in legislation in Western Australia prohibiting the construction and operation of a repository for the disposal of imported nuclear waste, unless approved by both houses of the WA Parliament. Within the scientific, technical and business communities, there has been much greater readiness to objectively weigh up the pros and cons of hosting an international disposal facility. The public reaction has been mixed, with some individuals and communities strongly opposing the concept whilst others are prepared to seek information before judging the case on its merits.Meanwhile, on the world stage, the generic concept of international disposal facilities continues to be elaborated - including defining better the roles which such facilities could play in management and disposition of surplus weapons material. In addition contacts are being strengthened with potential users of such facilities and actions being taken to intensify Pangea's activities in other countries identified as having potential host regions for a high-isolation repository of the type proposed by Pangea.

EXAFS and XANES Analysis of Plutonium and Cerium Edges From Titanate Ceramics for Fissile Materials Disposal

We report x-ray absorption near edge structure (XANES) and extended x-ray absorption fine structure (EXAFS) spectra from the plutonium L{sub III} edge and XANES from the cerium L{sub II} edge in prototype titanate ceramic hosts. The titanate ceramics studied are based upon the hafnium-pyrochlore and zirconolite mineral structures and will serve as an immobilization host for surplus fissile materials, containing as much as 10 weight % fissile plutonium and 20 weight % (natural or depleted) uranium. Three ceramic formulations were studied: one employed cerium as a ''surrogate'' element, replacing both plutonium and uranium in the ceramic matrix, another formulation contained plutonium in a ''baseline'' ceramic formulation, and a third contained plutonium in a formulation representing a high-impurity plutonium stream. The cerium XANES from the surrogate ceramic clearly indicates a mixed III-IV oxidation state for the cerium. In contrast, XANES analysis of the two plutonium-bearing ceramics shows that the plutonium is present almost entirely as Pu(IV) and occupies the calcium site in the zirconolite and pyrochlore phases. The plutonium EXAFS real-space structure shows a strong second-shell peak, clearly distinct from that of PuO{sub 2}, with remarkably little difference in the plutonium crystal chemistry indicated between the baseline and high-impurity formulations.

EELS and Xanes Analysis of Plutonium and Cerium Edges From Titanate Ceramics for Fissile Materials Disposal

Abstract We report x-ray absorption near edge structure (XANES) and extended x-ray fine structure analysis (EXAFS) spectra from the plutonium Llll and cerium Lm edges in prototype titanate ceramic hosts for disposal of surplus fissile materials. These spectra were obtained using the MRCAT beamline at the Advanced Photon Source (APS). The XANES and EXAFS results are compared with electron loss spectra (EELS) determination of oxidation state from the plutonium MlV,V and cerium MlV,V edges [1,2]. The titanate ceramics studied are based upon the hafniumpyrochlore and zirconolite mineral structures and will serve as an immobilization host, containing as much as 10 weight % fissile plutonium, and 20 weight % (natural or depleted) uranium. Similar formulations were composed using cerium as a “surrogate” element, replacing both plutonium and uranium in the ceramic matrix. We find the plutonium to be present almost entirely as Pu (IV), while the cerium is clearly in a mixed III-IV oxidation state in the surrogate ceramic.

MANAGING MILITARY URANIUM AND PLUTONIUM IN THE UNITED STATES AND THE FORMER SOVIET UNION

▪ Abstract Effective approaches to the management of plutonium and highly enriched uranium (HEU)—the essential ingredients of nuclear weapons—are fundamental to controlling nuclear proliferation and providing the basis for deep, transparent, and irreversible reductions in nuclear weapons stockpiles. The collapse of the Soviet Union and the ongoing dismantlement of tens of thousands of nuclear weapons are creating unprecedented stresses on the systems for managing these materials, as well as unprecedented opportunities for cooperation to improve these systems. In this article, we summarize the technical background to this situation, and the current and prospective security challenges posed by military stockpiles of these materials in the United States and Russia. We then review the programs in place to address these challenges, the progress of these programs to date, and the work remaining to be done, in five areas: (a) preventing theft and smuggling of nuclear warheads and fissile materials; (b) building a regime of monitored reductions in nuclear warhead and fissile material stockpiles; (c) ending further production of excess fissile materials; (d ) reducing stockpiles of excess fissile materials; and (e) avoiding economic collapse in the nuclear cities where substantial fractions of these materials and their guardians reside.

The design rationale of the IFR

The Integral Fast Reactor (IFR) concept has been developed over the last ten years to provide technical solutions to perceptual concerns associated with nuclear power. Beyond the traditional advanced reactor objectives of increased safety, improved economy and more efficient fuel utilization, the IFR is designed to simplify waste disposal and increase resistance to proliferation. Only a fast reactor with an efficient recycle technology can provide for total consumption of actinides. The basic physics governing reactor design dictates that, for efficient recycle, the fuel form should be limited in burnup only by radiation damage to fuel cladding. The recycle technology must recover essentially all actinides. In a fast reactor, not all fission products need to be removed from the recycled fuel, and there is no need to produce pure plutnium. Recovery, recycle, and ultimate consumption of all actinides resolves several waste-disposal concerns. The IFR can be configured to achieve safe passive response to any of the traditional postulated reactor accident initiators, and can be configured for a variety of power output levels. Passive heat removal is achieved by use of a large inventory sodium coolant and a physical configuration that emphasizes natural circulation. An IFR can be designed to consume excess fissile material, to produce a surplus, or to maintain inventory. It appears that commercial designs should be economically competitive with other available alternatives.

Economic analysis of a magnetic fusion production reactor

The magnetic fusion reactor for the production of nuclear weapon materials, based on a tandem mirror design, is estimated to have a capital cost of $1.5 billion and to produce 10 kg of tritium/year for $22,000/g or 940 kg/year of plutonium in the plutonium mode for $250/g plus heavy metal processing. A tokamak-based design is estimated to cost $1.5 billion and to produce 10 kg of tritium/year for $29 thousand/g. For comparison, a commercially sized tandern mirror fusion breeder selling excess electricity and fissile material to commercial markets is estimated to cost $3.6 billion and to produce tritium for $2.6 thousand/g and plutonium for $34/g plus heavy metal processing.