Microstructure of Aged 238 Pu-doped La-monazite Ceramic and Peculiarities of its X-ray Emission Spectra
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MRS Advances © 2020 Materials Research Society DOI: 10.1557/adv.2020.53
Microstructure of Aged 238Pu-doped La-monazite Ceramic and Peculiarities of its X-ray Emission Spectra 1,2
Andrey A. Shiryaev, 3Boris E. Burakov, 4Vasily O. Yapaskurt, 2Alexander V. Egorov, 2Irina E. Vlasova
1 Institute of physical chemistry and electrochemistry RAS, Leninsky pr. 31, korp. 4, 119071, Moscow, Russia ([email protected])
2
Department of Chemistry, Lomonosov Moscow State University, Leninskie gory, 1 bld.3, Moscow, 119991, Russia
3
V. G. Khlopin Radium institute, 2-nd Murinski ave. 28, Sankt-Petersburg, 194021, Russia.
4
Department of Geology, Lomonosov Moscow State University, Moscow, 119991, Russia
Abstract New data on microstructure of 16 years old (La, Pu)PO4 monazite ceramics doped with 8.1 wt% of 238Pu are presented. It is shown that the sample consists from at least two phases differing in La/Pu ratio and small precipitates of Pu-phosphate. Possible mechanisms of the compositional heterogeneity are discussed. Formation of Pu-containing rhabdophane after sample storage in air is observed. This phenomenon together with gradual mechanical destruction of the ceramic pellet formation of submicron particles will likely increase rate of radionuclides loss from the monazite-based waste form. X-ray emission lines produced by recoil uranium ions from Pu decay are analysed. It is suggested that careful examination of their relative intensities may provide important information about behaviour of "hot" recoils in nuclear waste forms.
Introduction. Monazite-based materials are considered as promising forms for long-term immobilization of actinides (e.g. [1]). Despite relatively good understanding of structure 1
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of monazites containing REE elements and actinides [2], information about evolution of actinide-containing samples with high degree of self-irradiation remains limited. Here we present new data on microstructure of (La, Pu)PO4 monazite ceramics containing in total 11 wt.% of Pu (calculated for metal) with predominant fraction of 238Pu (8.1 wt% of total sample mass) which was synthesized in 2002 [3]. Results of leaching tests of a piece of this sample were presented in [4]; for data on Raman spectra and some TEM data for 11 y.o. sample see [5].
Experimental. The sample of (La, Pu)PO4 monazite ceramic was synthesized in July 2002 by coprecipitation of La/Pu from respective aqueous nitrate solutions using ammonium hydrophosphate. Total Pu content (calculated for metal) was 11 wt.% (8.1 wt.% 238Pu and ~3 wt% 239Pu). The precipitated powder was rinsed in water and dried at 100°C for 1 hour in air. Then the powder was calcined in air at 700°C for 1 hour, milled in an agate mortar, and cold pressed into pellets 10 mm in diameter. Subsequent sintering in air at 1200-1250°C for 2 hou
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