Immobilization of Radioactiveand Rare-Earth Element Wastes
The Study of the Immobilization of Pu, Sr+Cs and Rare-Earth Element Waste Fractions from Spent Nuclear Fuel and Weapon Materials Reprocessing
Tech Area / Field
- ENV-RWT/Radioactive Waste Treatment/Environment
8 Project completed
Senior Project Manager
Wol'f O V
A.N.Frumkin Institute of Physical Chemistry and Electrochemistry, Russia, Moscow
- NPO Mayak, Russia, Chelyabinsk reg., Oziorsk\nAll-Russian Scientific Research Institute of Non-Organic Materials named after A. Bochvar, Russia, Moscow
- Sandia National Laboratories, USA, NM, Albuquerque\nArgonne National Laboratory (ANL) / West, USA, ID, Idaho Falls
Project summaryThe future of the nuclear industry is mostly dependent upon whether high-level wastes will be disposed of safely and economically. Presently, as it is accepted in multiple nuclear countries, they are subject to vitrification and then sent for temporary storage and eventual disposal to a geologic repository. Such an approach is complicated with residual radioactivity of the wastes, since they contain long-term radionuclides (basically, actinides) and therefore must be monitored during storage for several thousands of years.
To reduce the waste’s radioactivity rate, a suggestion was made to fractionate it into a series of groups or fractions: long-term radionuclides (actinides), rare-earth elements (REE) and Sr combined with Cs. The fractions separated are then immobilized into stable matrices, stored and finally disposed of in geologic formations.
At present the idea of fractionating the wastes and, respectively, of separating the most long-term and toxic radionuclides, transplutonic, REE, and Sr+Cs fractions is actively under assessment. The problem of dealing with the most long-term fractions is one of the serious issues of the nuclear industry. After partitioning, the wastes contain short-term isotopes and are not so perilous as the said long-term ones. In the Russian Federation at PA “Mayak” a facility has been constructed and is now operational for fractionating the wastes, with the extraction of Cs and Sr by cobalt dicarbolide.
ISTC Project #504-97 (expired in 31/10/2000) completed a considerable volume of research for the selection of glass-like, mineral-like and ceramic matrices for immobilizing Plutonium, a dangerous radionuclide from the transplutonic element group. A wide spectrum of solid mineral-type matrices – basalt materials modified with boron additives (B2O3, CaO*2B2O3), cast stone and chromite-niobate compositions were evaluated. However, many of the technologic issues (especially the equipment option - cold-crucible inductive melting and hot pressing) were excluded from the research. Also, the study made was not associated with fractionating. For example, ISTC Project #504-97 did not touch any aspect related to the selection of an optimum waste immobilization flow sheet, development of matrices or the immobilization technology of the most bulky wastes, such as REE and Sr+Cs.
Those issues, as well as others which arose at the end of the Project, from our standpoint, should be resolved in a new Project. Particularly, we propose to develop technology for the immobilization of REE and Sr+Cs waste fractions. Some of this work has been already performed at IPC RAS for the creation of powerful heat and radiation sources. However, such developments cannot be used for the immobilization of the above-mentioned fractions due to higher concentrations of the isotopes in the matrix and its weak properties (for example, the high content of Cs and Sr in the matrix, 60% wt, results, predominantly, in the leaching of components of the material). Also, the work was carried out only for cesium and strontium sources independently.
The purposes of the Project Proposal are:
1. Development of ecologically secure methods for the immobilization of Pu, REE and Cs-Sr of containing fractions of liquid radioactive waste (LRW) from the processing of spent nuclear fuel in the form of chemically, thermally and radiation-hardened glass-like, ceramic mineral-like and composite matrixes, and the definition of technological parameters of their smelting, manufacture and compacting.
2. Improvement of technology for the manufacture of protective containers from stone casting with the purpose of introducing a padding protective barrier to increase the safety of the burial of radioactive waste.
3. Verification of designed methods of technologies and structures of matrixes for immobilization of fractions of liquid radioactive waste (LRW) with the purpose of intrusion in industry.
The new ISTC Project, continuing and evolving former ISTC Project 504-97, will focus on the development of matrices and immobilization processes for Cs and Sr apart, Sr+Cs, and REE waste fractions. In addition, other matrices, which were not covered by the earlier project, #504-97, must be investigated and selected. A study will be accomplished for matrices of various purpose, including ones for temporary storage of Sr+Cs fractions with their eventual reuse as heat sources or for medical purposes. Optionally, matrices could be developed for securing the radionuclides and for their disposal in geologic formations. The development of those matrices needs to be accompanied with the elaboration of new technologies and research of their synthesis regimes.
The disposition of immobilized wastes into containers made from basalt and stone cast will be also continuously researched. It is necessary to scrutinize the way that the containers are sealed and to define reliable regimes for connecting containers with hoods, and regimes of their cooling. All these tests will be implemented at a facility designed in last months of Project # 504-97. It would help to clarify numerous areas of uncertainty, which could affect the sealing and design specifications of the containers.
During the work a study will be made to extract the most dangerous fractions of the high-level wastes, such as transuranic (Pu, Np) and transplutonic (Am, Cm) elements, REE, and Sr+Cs fractions. A process of immobilizing them into vitreous and mineral-type matrices will be made using a cold-crucible inductive melting (CCIM) facility. Efforts will be also applied to immobilize alpha-radioactive solid and liquid wastes of chemical-metallurgic production with the selection of optimum processes and equipment, to define physico-chemical and mineralogical properties of the solidified wastes.
In the process of MOX fuel fabrication from weapons- and energy-grade Plutonium solid and liquid Pu-containing wastes are being generated. When MOX-fuel production operations go on, liquid and solid wastes could be solidified into natural or hand-made forms of 10-6-10-8 g/cm2*day hydrolytic stability.