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Influence of accessory phases and surrogate type on accelerated leaching of zirconolite wasteforms

DOI: 10.1038/s41529-021-00171-8 DOI Help

Authors: Lewis R. Blackburn (University of Sheffield) , Rachel Crawford (University of Sheffield) , Samuel A. Walling (University of Sheffield) , Laura J. Gardner (University of Sheffield) , Max R. Cole (University of Sheffield) , Shi-Kuan Sun (University of Sheffield) , Clemence Gausse (University of Sheffield) , Amber R. Mason (University of Sheffield) , Martin C. Stennett (University of Sheffield) , Ewan R. Maddrell (National Nuclear Laboratory) , Neil C. Hyatt (University of Sheffield) , Claire L. Corkhill (The University of Sheffield)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Npj Materials Degradation , VOL 5

State: Published (Approved)
Published: May 2021
Diamond Proposal Number(s): 17243

Open Access Open Access

Abstract: A fraction of the UK Pu inventory may be immobilised in a zirconolite ceramic matrix prior to disposal. Two zirconolite compositions, targeting CaZr0.80Ce0.20Ti2O7 and CaZr0.80U0.20Ti2O7, were fabricated by hot isostatic pressing, alongside a reformulated composition, nominally Ca0.80Zr0.90Ce0.30Ti1.60Al0.40O7, with an excess of Ti and Zr added to preclude the formation of an accessory perovskite phase. Materials were subjected to accelerated leaching in a variety of acidic and alkaline media at 90 °C, over a cumulative period of 14 d. The greatest Ce release was measured from CaZr0.80Ce0.20Ti2.00O7 exposed to 1 M H2SO4, for which 14.7 ± 0.2% of the original Ce inventory was released from the wasteform into solution. The extent of Ce leaching into the solution was correlated with the quantity of perovskite present in the wasteform, and associated with the incorporation and preferential dissolution of Ce3+. CaZr0.80U0.20Ti2.00O7 exhibited improved leach resistance relative to CaZr0.80Ce0.20Ti2.00O7, attributed to the decreased proportion of accessory perovskite, with 7.1 ± 0.1% U released to in 8 M HNO3 after 7 d. The Ca0.80Zr0.90Ce0.30Ti1.60Al0.40O7 composition, with no accessory perovskite phase, presented significantly improved leaching characteristics, with < 0.4%Ce released in both 8 M HNO3 and 1 M H2SO4. These data demonstrate the need for careful compositional design for zirconolite wasteforms with regard to accessory phase formation and surrogate choice.

Journal Keywords: Corrosion; Nuclear waste

Subject Areas: Materials, Chemistry, Earth Science


Instruments: B18-Core EXAFS

Other Facilities: BL-27 at Photon Factory Synchrotron

Added On: 26/05/2021 11:48

Documents:
s41529-021-00171-8.pdf

Discipline Tags:

Earth Sciences & Environment Radioactive Materials Mineralogy Corrosion Materials Science Nuclear Waste Geology

Technical Tags:

Spectroscopy X-ray Absorption Spectroscopy (XAS) X-ray Absorption Near Edge Structure (XANES)