Profiling hot isostatically pressed canister–wasteform interaction for Pu‐bearing zirconolite‐rich wasteforms

Abstract

Zirconolite‐rich full ceramic wasteforms designed to immobilize Pu‐bearing wastes were produced via hot isostatic pressing (HIP) using stainless steel (SS) and nickel (Ni) HIP canisters. A detailed profiling of the elemental compositions of the major and minor phases over the canister–wasteform interaction zone was performed using scanning electron microscopy combined with energy‐dispersive X‐ray spectroscopy (SEM‐EDS) characterization. Bulk sample analyses from regions near the center of the HIP canister were also conducted for both samples using X‐ray diffraction and SEM‐EDS. The sample with the Ni HIP canister showed almost no interaction zone with only minor diffusion of Ni from the inner wall of the canister into the near‐surface region of the wasteform. The sample with the SS HIP canister showed ∼100–120 μm of interaction zone dominated by high‐temperature Cr diffusion from canister materials to the wasteform with the Cr predominantly incorporated into the durable zirconolite phase. We also examined, for the first time, changes to the HIP canister wall thickness caused by HIPing and demonstrated that no canister wall thinning occurred. Instead, in the areas examined, the canister wall thickness was observed to increase (up to ∼20%) due to the compression occurring during the HIP cycle. Further, only sparse formation of (Cr, Mn)‐rich oxide particles were noted within the HIP canister inner wall area immediately adjacent to the ceramic material, with no evidence for reverse diffusion of ceramic materials. Though the HIP canister–wasteform interaction extends to ∼120 μm when using an SS HIP canister for the system investigated, this translates to <<1 vol.% for an industrial scale HIPed wasteform. Importantly, the HIP canister–wasteform interactions did not produce any obviously less durable phases in the wasteform or had any detrimental impact on the HIP canister properties.

Effect of Ti‐metal addition on hot‐isostatically pressed (HIPed) Synroc‐C

“…In addition, the composition of selected grains matched that of loveringite, (CaSrNd) 1 (Ti, Al, Fe, Zr, Mo, Ag) 21 O 38 (Table S2), which was also evident in the XRD data (Figure 2). Again, the presence of loveringite in similar compositions under reducing conditions was reported previously 32 . The TEM‐EDS analysis also showed evidence for phases rich in Cs and Mo (Table S2) in the 8 wt.% Ti sample, although it was not possible to confirm the identity of these phases from the XRD and EDS data.…”

“…Again, the presence of loveringite in similar compositions under reducing conditions was reported previously. 32 The TEM-EDS analysis also showed evidence for phases rich in Cs and Mo (Table S2) in the 8 wt.% Ti sample, although it was not possible to confirm the identity of these phases from the XRD and EDS data. In separate work, the formation of CaTiO 3 and such calcium aluminate phases have been observed previously when undertaking reactions of CaCO 3 and Al 2 O 3 with Ti powder.…”

Zirconolite Polytypes and Murataite Polysomes in Matrices for the REE—Actinide Fraction of HLW

“…For the immobilization of actinide containing nuclear waste, crystalline zirconolite and glass-crystalline materials with zirconolite have been proposed. They may be obtained by all known methods—sintering at atmospheric or elevated pressures, melting and crystallization, high-speed pulsed electric current sintering, and self-propagating high-temperature synthesis [ 57 , 72 , 73 , 74 , 75 , 76 , 77 , 78 , 79 , 80 , 81 , 82 , 83 , 84 , 85 , 86 , 87 , 88 , 89 , 90 , 91 , 92 ]. Zirconolite is stable in various natural conditions [ 22 , 24 , 25 , 75 ]; natural zirconolite is a rare mineral of terrestrial and lunar igneous rocks, and metasomatites.…”

“…In many early [ 28 , 72 , 73 , 98 , 114 , 115 ] and more recent [ 92 , 116 , 117 ] studies of matrices, the zirconolite polytype was not specified. There are several explanations for this and the first is that the similarity of properties [ 80 ] may make it unnecessary to identify the exact zirconolite polytype.…”

Characterisation of a Complex CaZr0.9Ce0.1Ti2O7 Glass–Ceramic Produced by Hot Isostatic Pressing

“…The majority of HIP canisters utilised for development of nuclear wasteforms are made of stainless steel, which exerts a mild reducing atmosphere at HIP temperatures. Previous work has examined the interactions of the ferrous canister with zirconolite or high zirconolite content ceramics, with the major observations being that formation of Cr oxides (usually approximately 20 µm thick) is the major product of reaction with the canister, with the zirconolite phase compositions varying based on their proximity to the canister (often enriched in Fe and/or Cr, usually approximately 60 µm thick) [18][19][20].…”