Mechanical integrity of yttria-stabilised zirconia doped with Np oxide
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Mechanical integrity of yttria-stabilised zirconia doped with Np oxide Hajime Kinoshita1*, Ken-ichi Kuramoto2, Masayoshi Uno1, Shinsuke Yamanaka1, Hisayoshi Mitamura3 and Tsunetaka Banba3 1
Department of Nuclear Engineering, Osaka University, Suita, Osaka 565-0871, Japan 2 Department of Nuclear Energy System, Japan Atomic Energy Research Institute, Tokai-mura, Ibaraki 319-1195, Japan 3 Department of Environmental Sciences, Japan Atomic Energy Research Institute, Tokai-mura, Ibaraki 319-1195, Japan * Current address: Immobilisation Science Laboratory, The University of Sheffield, Sheffield, S1 3JD, UK ABSTRACT Mechanical properties of YSZ doped with Np oxide were studied to investigate the sufficiency to be a waste form for immobilisation of highly concentrated TRU. The study was conducted focusing on Vickers (HV) and Knoop (HK) hardness, Young’s modulus (E) and fracture toughness (KIC). The results showed that YSZ is harder and more resistant to elastic deformation and crack development than such waste forms as borosilicate glass and synroc. The effects of porosity and Np content on HV, HK, E and KIC are also discussed.
INTRODUCTION Isolation of hazardous radionuclides from the biosphere is the most important objective in the management of high level radioactive waste (HLW) arising from reprocessing spent nuclear fuels. In particular, transuranium (TRU) elements as Np, Pu, Am and Cm must be treated with special care because of their long half-lives. The general objective of the present work is to study the mechanical integrity of yttriastabilised zirconia (YSZ) when used as a host matrix for immobilisation of partitioned and highly concentrated transuranium (TRU) waste. Our previous studies of YSZ have demonstrated that YSZ can accommodate high concentrations of Np, Ce or Nd [1, 2] and that YSZ solid solutions doped with Np, Ce or Nd have remarkably high chemical durability [1, 2]. More specifically, the present study aims to (i) investigate whether YSZ doped with Np has suitable mechanical properties, (ii) evaluate the effect of porosity and Np content on the mechanical properties and (iii) estimate the concentration of Np which can be incorporated into YSZ while still maintaining sufficient mechanical integrity to function as a waste form. The study has been conducted focusing on Vickers (HV) and Knoop (HK) hardness, Young’s modulus (E) and fracture toughness (KIC). The Young’s modulus and fracture toughness provide measures of the resistance to elastic deformation and resistance to crack development in brittle materials, respectively. The fracture toughness is especially important for waste forms because the premature failure or fracture would increase the surface area of the waste form, which could affect the leaching behaviour.
In the first part, the mechanical properties of Np-doped YSZ are compared with those of borosilicate glass and Synroc-C, together with the data of Ce and/or Nd-doped YSZ. Cerium and Nd are often used as surrogates for tetra- and tri-valent actinides, respectively [3-5]. The second pa
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