S. Moricca

Endohedral fullerene formation through prompt gamma recoil

Abstract Neutron activation of rare gases trapped interstitially in the lattice of C 60 has been studied. Gamma spectroscopy of the neutron irradiated solids and solutions of them in toluene provided strong evidence that 1–2% of the activated rare gas atoms, which recoil as a result of prompt gamma emission following neutron activation, become entrapped in what is most likely to be the C 60 molecule or some other fullerene derivative. From these results we postulate the formation of RN@C 60 where the radionuclide (RN) is 125g Xe, 133g Xe, 135g Xe, 41 Ar or 85m Kr.

Gas storage in fullerenes

Abstract Fullerenes and in particular C60 have been shown to store effectively a wide range of gases from simple monatomic rare gases to diatomics and polyatomics. A review of the research in this area conducted at ANSTO is given. The trapping of Ar, Kr, Xe, and CO2 are discussed in detail whilst preliminary results pertaining to N2O, CH4, CF4, C2H6 and SF6 are also reported. A range of techniques have been used to elucidate both the structure of the new fullerene intercalated solid and the trapped gas itself. The preponderant techniques used, include infra-red absorption spectroscopy (IR), X-ray powder diffraction a (XRD), neutron powder diffraction (NRD), transmission electron microscopy (TEM), and thermal gravimetric analysis (TGA).

Structural Characterization of the New Fullerene-Rare Gas Compound Ar1C60

Abstract We communicate how C60 Hot Isostatically Pressed (HIPed) at 200° or 400°C with a pressure of 1.7 kbar of Ar produces the new fullerene-rare gas compound Ar1C60. We have shown, using Xray powder diffraction and subsequent Rietveld analysis, that this solid can be characterised stoichiometrically as Ar1C60- The stoichiometry has also been confirmed by thermal gravimetric analysis (TGA) showing 5% by weight to be Ar (expected=5.25%). The presence of Ar is confirmed by transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). This material is found to be remarkably stable to loss of Ar over several weeks at room temperature. This represents the first full characterisation of an interstitial rare gas fullerene compound. †Deceased. This letter is dedicated to the living memory of Dr. R. Lindsay Davis. His wisdom and encouragement are intangibly woven into this work

Endohedral Formation from Neutron Activation of Interstitial Rare Cas C60 Fullerides

Abstract Rare gas interstitial fullerenes, produced by hot isostatic pressing solid C60 in the presence of Ar, Kr or Xe, have been neutron irradiated and their behaviour investigated. The activity of the generated radionuclides was found to be in agreement with calculations and this combined with X-ray powder diffraction showed that both the activated radionuclides and the unactivated rare gas remained trapped in the solid after they have been subjected to the harsh conditions encountered in a nuclear reactor. Gamma spectroscopy of the irradiated solids and solutions of them in toluene provided strong evidence for endohedral compound formation. We estimate 1–2% of the activated rare gas atoms, which recoil as a result of prompt gamma emission, end up in the centre of what is most likely too be the C60 molecule or some other fullerene derivative. On this basis, we postulate the formation of RN@C6o where the radionuclide (RN)is 125gXe, 133gXe, I35gXe, 41Ar or85mKr.

Advantages Hot Isostatically Pressed Ceramic and Glass-Ceramic Waste Forms Bring to the Immobilization of Challenging Intermediate- and High-Level Nuclear Wastes

Hot isostatic pressing (HIP) is a technology with wide applicability in consolidating calcined intermediate-level and high-level nuclear waste, especially with wastes that are not able to be readily processed by vitrification at reasonable waste loadings. The essential process steps during the HIP cycle will be outlined. We have demonstrated the effective consolidation via HIP technology of a wide variety of tailored glass-ceramic and ceramic waste forms, notably simulated ICPP waste calcines, I sorbed upon zeolite beads, Pu-bearing wastes, inactive Cs/Sr/Rb/Ba mixtures, simulated waste pyroprocessing salts from spent nuclear fuel recycling, Tc, U-rich isotope production waste, and simulated K-basin (Hanford, WA, USA) and Magnox sludges (UK). Can-ceramic interactions have been carefully studied. The principal advantages of the HIP technology include: negligible offgas during the high temperature consolidation step, relatively small footprint, and high waste loadings. As a batch process, the wasteform chemistry can be readily adjusted on a given process line, to deliver wastes into different end states (e.g. direct HIP versus chemically tailored). This flexibility allows the treatment of multiple waste streams on the one process line.

Immobilisation of Higher Activity Wastes from Nuclear Reactor Production of 99Mo

A variety of intermediate- and low-level liquid and solid wastes are produced from reactor production of 99Mo using UAl alloy or UO2 targets and in principle can be collectively or individually converted into waste forms. At ANSTO, we have legacy acidic uranyl-nitrate-rich intermediate level waste (ILW) from the latter, and an alkaline liquid ILW, a U-rich filter cake, plus a shorter lived liquid stream that rapidly decays to low-level waste (LLW) standards, from the former. The options considered consist of cementitious products, glasses, glass-ceramics, or ceramics produced by vitrification or hot isostatic pressing for intermediate-level wastes. This paper discusses the progress in waste form development and processing to treat ANSTO’s ILW streams arising from 99Mo. The various waste forms and the reason for the process option chosen will be reviewed. We also address the concerns over adapting our chosen process for use in a hot-cell environment.

Novel rare gas interstitial fullerenes of C70

Abstract The formation and characterisation of the rare gas interstitial compounds of argon, krypton and xenon with C70 are presented. The materials were produced by hot-isostatically pressing (HIPing) powdered samples of C70 at a temperature of 400 °C and under a surrounding rare gas pressure between 170 and 200 MPa for ~ 12 h. The materials were analysed by thermogravimetric analysis (TGA) and X-ray powder diffraction (XRD). It appears that under the HIP conditions used we were able to saturate all octahedral sites of the C70 lattice (experimental error 5–10%), giving the rare gas stoichiometric materials Ar1C70, Kr1C70 and Xe1C70. The C70 rare gas fullerenes were found to be more susceptible to loss of rare gas, compared with the corresponding C60 materials, although the relative stabilities followed the same pattern, with heavier intercalated rare gases being lost more slowly. The argon is lost very easily (within a few days) whereas the krypton and xenon C70 fullerenes were found to be stable at room temperature for several months, with some loss from the krypton fullerene.

The Use of Hot-Isostatic Pressing to Process Nuclear Waste Forms

ANSTO has developed a combination of tailored nuclear waste form chemistries coupled with the use of flexible hot-isostatic pressing processing technology to enable the successful incorporation of problematic nuclear wastes into dense, durable monoliths. This combined package also enables the design of waste forms with waste loadings well in excess of those achievable via baseline melting routes using borosilicate glass, as hot-isostatic pressing is not constrained by factors such as glass viscosity, crystallisation and electrical conductivity. In this paper we will discuss some of our experiences with problematic wastes, namely plutonium wastes, sludges and HLW such as the Idaho calcines.Copyright

Progress at ANSTO on a Synroc Plant for Intermediate-Level Waste from Reactor Production of 99Mo

Intermediate level waste from ANSTO’s expanded 99Mo production plant will consist of ~5000L/year of 6M NaOH + 1.4 NaAlO2 + fission products. Detailed engineering is being carried out on a synroc plant to immobilise this waste in a glass-ceramic, with completion scheduled for 2016. The liquid waste will be mixed with precursors and dried before being calcined in a reducing atmosphere to control fission product volatility. The calcine will be transferred to 30L metal cans which will be hot isostatically pressed at 1000°C/30MPa for 2h, then cooled to room temperature and stored preparatory to final disposal. Laboratory scale waste form material will pass 90°C PCT tests. In addition, legacy intermediate level uranyl nitrate-based liquid waste from 99Mo production at ANSTO between the 1980s and 2005 via irradiation of UO2 targets will also be immobilised by the same process to form a Synroc-type waste form. Some examples illustrating the wide applicability of hot isostatic pressing to consolidate nuclear waste forms will be given showing the advantages for particular wastes, notably high waste loadings and the absence of off-gas in the high temperature consolidation step. The immobilisation of a variety of low-level liquid and solid wastes from 99Mo production will also be discussed.

Building Flexibility Into the Design of a Pilot Plant for the Immobilisation of Pu Containing Residues and Wastes

NNL and ANSTO on behalf of Sellafield Ltd have developed a process for the immobilisation of a range of Pu containing wastes and residues. Following the inactive demonstration of the technology the project is now focusing on the design of an active pilot plant capable of validating the technology and ultimately immobilising a waste inventory containing around 100kg plutonium. The diverse wastes from which it is uneconomic to recover Pu, require a flexible process with a wide product envelope capable of producing a wasteform suitable for disposal in a UK repository. Ceramics, glass ceramics and metal encapsulated wasteforms can be delivered by the process line which incorporates size reduction and heat treatment techniques with the aim of feeding a hot isostatic pressing process designed to deliver the highly durable wasteforms. Following a demonstration of feasibility, flowsheet development is progressing to support the design which has the aim of a fully flexible facility based in NNL’s Central Laboratory on the Sellafield site. Optimisation of the size reduction, mixing and blending operations is being carried out using UO2 as a surrogate for PuO2. This work is supporting the potential of using an enhanced glass ceramic formulation in place of the full ceramic with the aim of simplifying glove box operations. Heat treatment and subsequent HIPing strategies are being explored in order to eliminate any carbon from the feeds without increasing the valence state of the uranium present in some of the inventory which can result in an unwanted increase in wasteform volumes. The HIP and ancillary systems are being specifically designed to meet the requirements of the Sellafield site and within the constraints of the NNL Central Laboratory. The HIP is being configured to produce consolidated product cans consistent with the requirements of ongoing storage and disposal. With the aim of one cycle per day, the facility will deliver its mission of immobilising the identified waste and residues inventory within 3 years. During that period it will also be used to demonstrate the potential of this technology to deliver the immobilisation of a proportion of the UK plutonium stockpile that may not be suitable for use as MOx fuel should that decision be taken.Copyright