Single-step, high pressure, and two-step spark plasma sintering of UO2 nanopowders

E De Bona,L Balice,L Cognini,M Holzhäuser,K Popa,O Walter,M Cologna,D Prieur,T Wiss,G Baldinozzi

doi:10.1016/j.jeurceramsoc.2021.01.020

Abstract

Three different spark plasma sintering (SPS) treatments were applied to highly sinteractive, near-stoichiometric UO2.04 nanocrystalline (5 nm) powders produced by U(IV) oxalate hydrothermal decomposition at 170 °C. The sintering conditions for reaching 95 % theoretical density (TD) in regular SPS, high pressure SPS (HP-SPS), and, for the first time, two-step SPS (2S-SPS), were determined. Densification to 95 % TD was achieved at 1000 °C in regular SPS (70 MPa applied pressure), 660 °C in HP-SPS (500 MPa), and 650−550 °C in 2S-SPS (70 MPa). With the goal of minimising the grain growth during densification, the sintering treatments were optimised to favour densification over coarsening, and the final microstructures thus obtained are compared. Equally dense UO2 samples of different grain sizes, ranging from 3.08 μm to 163 nm, were produced. Room-temperature oxidation of the powders could not be avoided due to their nanometric dimensions, and a final annealing treatment was designed to reduce hyperstoichiometric samples to UO2.00.

Highlights

During reactor operation, oxide nuclear fuels undergo deep microstructural and chemical modifications that transform the fresh fuel into spent nuclear fuel (SNF)
-p Abstract e Three different Spark Plasma Sintering (SPS) treatments were applied to highly sinteractive, nearr stoichiometric UO2.04 nanocrystalline (5 nm) powders produced by U(IV) oxalate hydrothermal decomposition at 170 °C
With the goal of minimising the grain growth during densification, the sintering treatments were optimised to favour a densification over coarsening, and the final microstructures obtained are compared

Summary

19 August 2020 8 January 2021 9 January 2021

This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. -p Abstract e Three different Spark Plasma Sintering (SPS) treatments were applied to highly sinteractive, nearr stoichiometric UO2.04 nanocrystalline (5 nm) powders produced by U(IV) oxalate hydrothermal decomposition at 170 °C. With the goal of minimising the grain growth during densification, the sintering treatments were optimised to favour a densification over coarsening, and the final microstructures obtained are compared.

Introduction

Powder densification

Results and discussion