Plutonium Ceramic in Underground Storage
Study of Plutonium Ceramics Alteration under Conditions of Underground Disposal
Tech Area / Field
3 Approved without Funding
Khlopin Radium Institute, Russia, St Petersburg
- Lawrence Livermore National Laboratory, USA, CA, Livermore\nMassachusetts Institute of Technology (MIT) / Nuclear Engineering Department, USA, MA, Cambridge\nLos Alamos National Laboratory, USA, NM, Los-Alamos\nHarry Reid Center for Environmental Studies, USA, NV, Las-Vegas
Project summaryLong-term storage of radioactive waste is a continuing major concern and many questions remain unanswered concerning the durability of waste form especially with regard to chemical alteration, leacibility, transport, environmental interaction etc. The proposed investigation can provide some new information on issues of long term storage and disposal of high-level radioactive waste and the obtained data can be also useful for development of advanced ceramic fuel.
It is well known that the first matrices for solidification of liquid HLW and their immobilization were glasses. Crystalline compounds however are more preferable in most cases. Ceramic matrices exceed glasses in some features. The Synroc matrix developed in ANSTO was the first ceramic tested in large-scale production. Titanates formed Synroc have the analogues in nature such as hollandite, perovskite, zirconolite, rutile, spinel. These compounds were selected for HLW solidification just accordingly to these minerals’ stability in nature. The leach testing confirms the supremacy of Synroc over glass matrices.
The main goal of the Project is experimental modeling of behaviour of ceramic matrices used for immobilization of long-lived actinide (U, Pu, Np, Am, Cm) wastes including weapons-grade plutonium in water media at increased temperatures to study possible alteration processes which may take a place during underground storage. The ceramic matrices of following types: titanate-based ceramics developed by Lawrence Livermore National Laboratory (LLNL, USA), double-phase ceramic based on zircon, (Zr, An)SiO4, and zirconia, (Zr,An)O2, and composition based on cubic zirconia, (Zr, Gd, An)O2, developed by V.G. Khlopin Radium Institute (KRI, Russia) will be studied. The experiments with radioactive ceramic samples for modeling ceramic behavior in repository environment will be carried out for the following geological media: granite rocks of Nizhnekanskiy massif located close to Pu-Plant “GHK” (Siberia, Russia); porphyritic massif located close to Pu-Plant “Mayak” (Ural, Russia); tuff rocks of Yucca Mountains (USA) and artificial environment (solutions of acids and salts).
Ceramic samples of all three types required for alteration experiments have been synthesized in KRI in 1999-2000 in framework of LLNL Contract #B506203. Synthesis and analytical study were partly carried out in frame of ISTC Project #1063. During the work on ISTC Project PDG #1819 samples of Pu-doped ceramic intended for alteration experiments was selected and obtained from special repository and their certification was carried out.
It is intended to use water solutions simulated underground water of rock massifs surrounding repositories as external reagent. Also the experiment in more aggressive media such as acid solutions and solutions of some carbonates or phosphates will be carried out.
Geochemical durability of ceramic matrices depends significantly from types of geological formations selected for waste-form disposal. Therefore the main attention will be paid to study of separate ceramic phases’ alteration, sorption of different ions on their surface, simultaneous measuring of leach rate and so on.
In frame of Project also will be carried out preliminary experimental study of ceramic powder transformation in several water media (silicate solution, perhaps brine or ferriferous solution) accordingly to methodic of metasomatic modeling at temperature 150-200. Numerous investigations and published data on metasomatic transformations of main types of rocks showed that it is very high-informative method. It allows taking results useful for prediction and evaluation of ceramic’s durability under conditions of geological disposal.
High-qualified experts of Radium Institute will carry out the Project. They are scientists skilled in development of ceramic matrices for immobilization of HLW including weapons-grade plutonium, scientists studied radionuclide migration in rocks after underground nuclear explosion, and mineralogists specialized in mineralogy of zircon and titanate minerals such as pyrochlore and perovskite group minerals and experts in different analytical technique.
During the work on ISTC Project Development Grant #1819 Russian scientist conducted additional study to elaborate the scope of activities and methods. Project Manager visited US and Work Plan for the project #1819.2 was presented and discussed with collaborators and their colleagues at US National Laboratories.
American specialists from LLANL, LLNL, MIT and the Harry Reid Center of UNLV supported the research and expressed their wishes to continue collaboration. They detailed that the experience will produce useful and important information that can be applied to model actinide disposal. Experimental data can be used to elaborate conditions for long-term storage and disposal of high-level waste. In addition, expert from LANL emphasized that the study of the alteration of actinide-doped ceramics is important not only for disposal of actinide wastes into geological formations, but also, for development of ceramic nuclear fuel (non-fertile fuel with inert matrix) for burning of excess weapons plutonium and transmutation of minor actinides. This area is of particular interest of current research of LANL in the framework of the Advance Fuel Initiative Program.
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