Structural peculiarities of aged 238 Pu-doped monazite
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Structural peculiarities of aged 238Pu-doped monazite Andrei A. Shiryaev1,2,3, Maximillian S. Nickolsky2, 1, Alexey A. Averin1, Mikhail S. Grigoriev1, Yan V. Zubavichus4, Irina E. Vlasova3, V. G. Petrov3, and Boris E. Burakov5 1 Institute of physical chemistry and electrochemistry RAS, Leninsky pr. 31, korp. 4, 119071, Moscow, Russia ([email protected]) 2 Institute of ore geology, petrography, mineralogy and geochemistry RAS, Staromonetny per, 35, 119017, Moscow, Russia 3 Department of Chemistry, Lomonosov Moscow State University, Leninskie gory, 1 bld.3, Moscow, 119991, Russia 4 NRC “Kurchatov institute”, Moscow, Russia 5 V. G. Khlopin Radium institute, 2-nd Murinski ave. 28, Sankt-Petersburg, 194021, Russia. ABSTRACT Results of characterization of 238Pu-doped Eu- and La-monazites using single crystal XRD, Raman and XAFS spectroscopy and TEM are presented. It is shown that despite significant accumulated doses (up to 9x1018 α-decays/gram) the Eu-monazite remains a single crystal. Unusual foamy structures are observed by TEM and are interpreted as recrystallisation of domains damaged by recoil U-ions. Partial recrystallisation of the surface material is also supported by Raman and luminescence data. INTRODUCTION Final safe disposal of excess weapons plutonium and minor actinides remains a problem for the future of nuclear energy. Whereas significant fraction of Pu can be recycled as MOX, REMIX, etc. fuels, re-use of fissile material rich in heavy Pu isotopes, of Pu scrap and residues is economically unfeasible. Nuclear glasses can be used for Pu-immobilisation to a limited extend, since even advanced compositions such as Lanthanide-borosilicate glasses (LaBS) fail to dissolve more than 4-5 wt% of PuO2, the excess of plutonium forms various precipitates [1, 2]. Ceramics remain the only reasonable option if long-term stability and small volume of the waste are required (e.g., [3]). Studies of polycrystalline samples (ceramics) are very important for practical applications, but detailed investigation of single crystals are required for detailed understanding of radiation-induced evolution of the material. It is known that pure PuPO4 monazite becomes amorphous even after moderate degree of selfirradiation of 0.9 х 1018 α-decays/g [4]. However, single crystals of REE monazite doped with several wt.% of Pu isotopes preserve crystallinity at much higher accumulated doses [3]. The optimal loading of Pu in monazite structure remains unknown. In this contribution we report data relative to the investigation of the behavior of monazite single crystals with composition Eu0.937Pu0.063PO4 doped with 238Pu (4.9 wt% 238Pu+1.1 wt% of other Pu isotopes) grown in December 2003 at V.G. Khlopin Radium institute [3] and with accumulated doses between ~8.59.3x1018 α-decays/g. The samples were stored at 25 °C. Evolution of color and morphological features of these crystals have been described before [3]: small spontaneously detached pieces and later formation of some sort of blister were observed on crystals surfaces (Fig. I). The orig
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