Natural and artificial minerals as matrices for immobilization of actinides

Abstract

The possibility of insulation of long-lived actinides for the entire period of their potential hazard, i.e., over a virtually infinite time, is the crucial problem in safe disposal of high-level radioactive wastes (HLW). The reality of such a possibility is corroborated by the study of natural radioactive minerals that firmly retain U, Th, and REE, which are close in geochemical properties to transuranic actinides, for millions of years despite the effects of groundwater. The natural analogues of actinide HLW matrices are minerals where U, Th, and REE are contained as major elements or isomorphic admixtures. The study of these minerals is helpful for synthesis of durable artificial forms of wastes that ensure reliable insulation of HLW up to the complete decay of actinides independently of such engineering barriers of underground repositories as containers and bentonite buffers. The main requirements on confinement matrices include a high isomorphic capacity with respect to actinides and other HLW components, chemical and radiation stability, and technological feasibility of their industrial production. The natural and artificial minerals-uraninite, monazite, zirconolite, pyrochlore, britholite, garnet, and murataitecharacterized in this paper may serve as a basis for efficient matrices for immobilization of actinide wastes.

Crystal chemistry of the monazite structure

“…calcium) and its capacity to incorporate large amounts of uranium and thorium yielded to propose their use in the field of long term storage of radioactive wastes. 5,[84][85][86][87][88][89][90][91][92][93] In the same way, the high resistance of monazite-type structure to radiation damages (either in the synthetic and natural forms) is probably connected to the easy recovery of these distorted polyhedra for very low temperatures of annealing. A lot of compositions were synthesized, yielding to the incorporation of various elements in terms of ionic radii and oxidation state in the monazite structure.…”

Amorphization of rare earth aluminate garnets under ion irradiation and decay of 244Cm admixture

“…The differ ence in the degree of crystallinity under close radiation doses is explained by the distinct rate of damage to natural and synthetic garnets. A similar difference is characteristic of other matrices and their natural ana logues (Lumpkin, 2001;Omel'yanenko et al, 2007). The effect of long lived 238 U decay on the structure of minerals is less in comparison with accelerated meth ods of radiation damage to synthetic phases caused by ion radiation and 244 Cm or 238 Pu decay.…”

“…Such a fraction commonly also contains REE occurring in waste. It is proposed to incorporate the An-REE fraction of HLW into synthetic crystalline matrices and dispose of them in underground reposi tories (Ringwood, 1985;Omel'yanenko et al, 2007). A number of phases are considered to be suitable for immobilization of An and REE (Radiocative…, 1988;Laverov et al, 2008), including aluminates and ferrites with garnet structure (Burakov et al, 1999;Yudintsev, 2003;Yudinsev et al, 2004;Yudintseva, 2005;Laverov et al, 2010).…”

“…Livshits. E mail: lito_232@igem.ru matrices (Lumpkin, 2001;Omel'yanenko et al, 2007). Minerals of the garnet group are almost com pletely devoid of actinides.…”

Sorption of Np(V) onto hybrid clay-based materials: Montmorillonite-melanoidin

“…After years of investigations, the deep geological disposal appears to be the best choice and the most internationally accepted solution for the storage of radioactive waste, since the geosphere is stable and secure on a long time scale [1,2]. The separation and transmutation of the radionuclides may be of interest in order to reduce the amount of nuclear waste, but there will be still high-level waste (HLW) which has to be considered.…”