Murataite-Based Ceramics for Actinide Waste Immobilization
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S.V. STEFANOVSKY, S.V. YUDINTSEV', B.S. NIKONOV*, B.I. OMELIANENKO, A.G. PTASHKIN * SIA "Radon", 7-th Rostovskii per., 2/14, Moscow 119121, Russia, itbstef~cityline.ru. **Institute of Geology of Ore Deposits (IGEM RAS), Staromonetny per., 35, Moscow 1091017, Russia, sergeygigem.msk.su. ***D.Mendeleev University of Chemical Technology, Miusskaya sq. 9, Moscow, Russia
ABSTRACT
Studying the Synroc, doped with a simulated HILW, we have found, along with conventional Synroc phases (zirconolite, perovskite, hollandite), an extra phase with a stoichiornetry (Ca,Mn,U,TR) 4 (U,TR,Zr,Ti) 2 (AI,Ti) 7 022. XRD and TEM study has shown this phase is related to a very rare mineral murataite. In the present work a ceramic based on murataite is studied. The ceramic samples in the system: Ca-Mn-Ti-Zr-U-Ce-AI-Fe-O were produced and examined in details using XRD, SEM/EDS, TEM, and optical microscopy. Total amount of actinide (U) and rare earth (Ce, Gd) elements in the murataite exceeds 20 wt.%. Isomorphic substitution schemes in the structures of synthetic and natural murataites are discussed. High isomorphic capacity of the murataite structure towards actinides and REEs, flexibility of its composition, feasibility of synthesis by melting, including a cold crucible melting, and very high chemical durability under hydrothermal conditions make the murataite-based ceramics very promising for actinides and excess weapon Pu fixation. INTRODUCTION
Actinides are one of the most dangerous components of high-level waste (HLW) having
5 8 very long half-life times requiring to be stored for 10 -10 years. Hence, for safe immobilization of
these elements matrices with excellent stability higher than borosilicate and alumophosphate glasses currently used for HLW solidification are required. Since the middle of 1970s titanatebased ceramics are considered to be the most promising host phases for immobilization of high level wastes (H-LW) and their components [1-4]. Recently in many countries, including Russia, HLW partitioning concept is discussed and implemented. Short-lived Cs/Sr and long-lived transuranic/rare earth (TRU-REE) fractions should be partitioned and immobilized in matrices separately [5]. For immobilization of actinide-containing wastes, including weapon-grade plutonium, the ceramics based on zirconolite, perovskite, pyrochlore, zirconia, zircon and others are suggested [6]. Recently, we have found in the ceramics containing simulated HLW of radiochemical plant "Mayak" a specific phase of complex and variable composition [7]. On the basis of its chemical and structural characteristics it was identified as synthetic analogue of natural mineral murataite. This phase has high uranium content of which was found to be higher than U content in co-existing zirconolite and perovskite by factors of 7... 10. We suggest this mineral can be promising host phase for actinides and REEs. To validate this suggestion a special study was carried out.
121 Mat. Res. Soc. Symp. Proc. Vol. 556
© 1999
Materials Research Society
EARLY STUDIES OF MUR
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