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Immobilization and Safe Storage of Plutonium Actinide Wastes

#2284


Nuclear Safe Ceramics for Compact Storage and Immobilization of Plutonium and Nuclear Power Engineering Actinide-Containing Wastes

Tech Area / Field

  • ENV-RWT/Radioactive Waste Treatment/Environment
  • ENV-WDS/Waste Disposal/Environment

Status
3 Approved without Funding

Registration date
20.08.2001

Leading Institute
VNIIEF, Russia, N. Novgorod reg., Sarov

Supporting institutes

  • All-Russian Scientific Research Institute of Non-Organic Materials named after A. Bochvar, Russia, Moscow

Collaborators

  • Forschungszentrum Karlsruhe Institut fur NuKcleare Entsorgungstechnik, Germany, Karlsruhe\nUniversity of Michigan / College of Engineering, USA, MI, Ann Arbor\nUniversity of California, USA, CA, Davis

Project summary

At the beginning of industrial atomic power exploration (in the 1960s), the nuclear power engineering challenge involved extensive plutonium breeding and uranium-238 involvement in the nuclear power cycle. Then fast breeder reactors were being designed and extensively studied; they were anticipated to breed plutonium for the continuously developing nuclear power engineering.

Presently, forty years hence, the focus in the nuclear power engineering has dramatically shifted. It transpired that there remains a sufficient amount of uranium fuel for NPP, and it is cheaper than plutonium fuel. The issues of safety in handling NPP radioactive wastes and, in the long-term, primarily plutonium and actinides have become of the highest priority. Nevertheless, plutonium as a valuable reactor fuel may well be demanded in future as a valuable reactor fuel.

In view of the reduction in nuclear weapons a large quantity of surplus weapons grade plutonium appeared. Plutonium is of a high environmental hazard, as in acts of God (fire, flood, etc.) air and water basins can be considerably contaminated because of its high toxicity. Therefore, comprehensive study of the issues of secure management of surplus weapons-grade plutonium and actinide wastes of nuclear power engineering is an important and topical problem.

ISTC Project #332B-97 involved issues of safe plutonium storage through the creation of critical-mass-free plutonium oxide – neutron poison compositions. This completely excludes immediate (without chemical reprocessing) utilization of retained plutonium in nuclear devices. It is possible to locate plutonium most compactly in the storage facility (at a density of 1 to 3 tons per cubic meter), which would result in smaller storage areas and lower storage costs. Compact burial of nuclear power engineering actinide wastes (of 10-15% plutonium mass concentration in material to be buried) has been widely discussed recently in literature.

The work carried out under ISTC Project #332B-97 demonstrated the feasibility of fabricating ceramic compositions containing plutonium and neutron poison in a ratio ensuring a critical-mass-free system using various methods. Hafnium in the form of oxide, carbide or oxycarbide; gadolinium in its oxide form, lithium in the form of hafnate or metaorthosilicate, and boron in a carbide form were used for the neutron poison. It is suggested that a number of critical-mass-free ceramic compositions imitating NPP actinide waste, containing materials to be buried, should be produced and studied in framework of the project.

The safety of long-term plutonium storage and actinide waste burial requires reliable knowledge in many scientific issues, pertaining to change in material properties during storage. The changes are expected to occur due to material self-irradiation in radioactive decay and under the action of enhanced temperature and pressure during the storage. Especial attention should be drawn to nuclear criticality issues (analysis of potential self-sustained chain fission reaction): an accurate account for neutron spectrum appearing in the burial site, study of the possible separation of spatial active material and neutron poison during the storage.

The objective of the project is to obtain new theoretical and experimental data characterizing nuclear safe plutonium base ceramics and NPP actinide waste behavior in self-irradiation and at enhanced temperatures and pressures during long storage.

The principal tasks of the project are:

• Preparation and study of nuclear safe binary and ternary Pu oxide ceramics with neutron poison. For the studies, 3 to 5 batches of homogeneous type one-phase and two-phase ceramic specimens and heterogeneous type specimens in the form of a ceramic skeleton, impregnated with actinide oxide sol ( 15 to 20 specimens in each batch), will be fabricated. The specimens fabricated previously under ISTC Project #332B-97, which were nuclear safe ceramics containing Pu and various neutron poisons, Hf, Gd, Li, B, will also be used for the study.


• Study of ceramics radiation behavior during self-irradiation. This includes studies of:
– radiation damage buildup kinetics during self-irradiation in various ceramics and system types, i.e. binary and ternary (Pu, Hf, Y oxide ceramics containing different neutron poisons, carbide and oxycarbide ceramics);
– changes in their structure and properties;
– behavior during storage of enamel coatings applied on the specimens, which are compositions of coated plutonium oxide microspheres and B4C.

• Study of some effects on composition stability:


– heating after radioactive irradiation, self-irradiation, of varying duration,
– isothermal annealing at possible self-heating temperature,
– heating under quasi-uniform compression pressure,which can develop in the Earth’s crust during storage in natural conditions.

• Theoretical computations of critical parameters for various developed plutonium compositions and NPP actinide wastes, analysis and development of models of material damage from alpha decay, thermal computations of radioactive material heating in the storage or burial conditions, assessments of the alpha decay effect on accelerating diffusion processes in ceramics.

There are only very few published papers devoted to self-irradiation effects on Pu-containing ceramic compound behavior and there are essentially none on nuclear-safe ceramics. The experimental data obtained under the proposed ISTC project will contribute to scientific information which pertains to the prediction of long-term actinide-containing waste behavior during storage.

As a result of Project implementation the following results will be obtained:


– new data on Pu ceramics behavior during self-irradiation by alpha decay products over about 5 years (with account of the duration of the studies begun under ISTC Project #332B-97),
– data on phase stability in time and ceramics structural components under quasi-uniform compression and non-uniform plastic deformation at room or higher temperatures,
– theoretical computations of critical parameters for various compositions to be developed, analysis and development of models of material damage from alpha decay, thermal computations of radioactive material heating in the storage or burial conditions, and assessments of the alpha decay effect on accelerating the diffusion processes in ceramics,
– data on behavior in time of coatings protecting against alpha particles.

The Project will be carried out by highly skilled specialists from VNIIEF and VNIINM who were earlier employed in nuclear weapons programs


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