IR and Raman Spectroscopy of Sodium-Aluminophosphate Glasses for Immobilizing High-Level Wastes from Spent Nuclear Fuel Reprocessing

Abstract

The structure of sodium-aluminophosphate glasses containing constituents of high-level wastes (cesium, magnesium, copper, and molybdenum oxides) from uranium-graphite reactors was studied by IR and Raman spectroscopy coupled with x-ray diffraction. The structural network was shown to be composed of short P-O chains with embedded AlO 4 tetrahedra. Cross-linking by Mg 2+ was possible in the Mg-bearing samples. The effect of the other oxides (Cs 2 O, MoO 3 , CuO) on the glass structure was negligible for the occurring amounts. The glasses devitrifi ed partially upon quenching and more strongly upon annealing. This was refl ected in splitting of the vibrational bands for bonds in the glass anionic structural motif.Introduction. High-level wastes (HLW) from extraction reprocessing of spent nuclear fuel (SNF) from VVER-440 and BN-600 reactors, maritime reactors, and research reactors are vitrifi ed at PA Mayak in an EP-500 electric furnace in order to produce sodium-aluminophosphate glass [1]. Plant PT-1 for reprocessing SNF from AMB-type uranium-graphite reactors is currently under reconstruction. HLW that are unavoidably produced by extraction reprocessing should also be sent to the EP-500 vitrifi cation furnace and incorporated into the phosphate glass [2]. Preliminary research used fi ve raffi nate simulants corresponding to the fi ve AMB SNF U + 9% Mo/Mg, U + 9% Mo/Ca, U + 3% Mo /Mg, UO 2 + Cu/Mg, and UO 2 + Mg. The research found that Mo and Cu had a negative effect on the quality of the sodium-aluminophosphate glasses that are used at PA Mayak to immobilize HLW. These components can cause the glass to segregate and/or crystallize with the separation of molybdates and/or spinels. This has a negative effect on the rheological properties of the melts and the chemical and thermal resistance of the fi nal glass forms [3]. We studied [4] previously the phase composition and element distribution between phases of glasses bearing HLW components of SNF from AMB reactors (Cs, Mo, Mg, Cu) using x-ray phase analysis (XPA) and scanning electron microscopy (SEM). It was shown that the glasses crystallized partially upon quenching and to a large extent upon annealing with the separation of aluminum, sodium-aluminum and sodium-cesium-aluminum orthophosphates from a (Na, Cs) 3x-3 Al x PO 4 solid solution. The Cs content could reach 0.32 formula units, which affected substantially its quantitative distribution among the occurring phases and eventually the chemical and radiation resistance of the glasses.Herein we present results from a study of glasses for immobilizing HLW of SNF from AMB reactors using IR vibrational and Raman spectroscopy.Experimental. Sodium-aluminophosphate glass used to vitrify HLW and medium-level wastes (MLW) in the EP-500 electric furnace was selected as the base glass [5]. The three principal components of the phosphate glass acted as the components of HLW simulants from extraction reprocessing AMB SNF. The mass fractions of Na, Al, and P oxides decreased proportionally. Sodium was replaced by cesium in ...

Dehalogenation reactions between halide salts and phosphate compounds

“…When formulating and synthesizing phosphate glasses containing high alkali contents, previous work can be drawn upon as well such as the work done with aluminophosphates, iron aluminophosphates, and iron phosphates where a range of phosphate precursors were used to produce glasses including P 2 O 5 , H 3 PO 4 , NaPO 3 , Al(PO 3 ) 3 , AlPO 4 , and NH 4 H 2 PO 4 ( Brow, 1993 ; Brow et al, 1993 ; Day et al, 1998 ; Mesko et al, 2000 ; Siemer, 2012 ; Stefanovsky et al, 2014 ; Stefanovsky et al, 2017 ; Bai et al, 2021 ). In a study by Bai et al (2021) directly comparing the same glass compositions produced with H 3 PO 4 with those made using NH 4 H 2 PO 4 , glasses made with H 3 PO 4 showed significantly higher Fe 3+ :Fe 2+ ratios based on Mössbauer spectroscopy, which can lead to more chemically resistant (higher chemical durability) waste forms ( Yu et al, 1997 ).…”