[en] The U.S. perspective on targets and timetables to reduce greenhouse gases was presented. While no new breakthroughs or headline-making events should be anticipated, the Unites States considers it reasonable to expect that the Conference of Parties (COP 4) in Buenos Aires will renew the momentum on implementing both the UN Framework Convention on Climate Change as well as the Kyoto Protocol. Emphasis should be placed on achieving the objectives of Kyoto by working towards an agreement on a work plan with timetables on the rules for the flexibility mechanisms, (emissions trading, the Clean Development Mechanism and Joint Implementation). The need for acknowledging the contributions to limiting greenhouse gases most countries have already made, on developing consensus on next steps and on avoiding unproductive arguments that lead to mistrust, was emphasized

[en] The immobilization of 13.5 wt% PuO₂ in a zirconolite-rich Synroc has been demonstrated at the 50 g PuO₂ scale in cans produced by hot isostatic pressing (HIPing) at 1280 C. The wasteform also contains more than an equimolar amount of neutron poisons such as Gd, Sm and Hf. The scale-up technology for production of Pu-containing cans of Synroc by HIPing has been demonstrated at the 10 kg scale using CeO₂ as an analog for PuO₂. The characterization of the products has shown that Ce is a good analog for Pu in zirconolite-rich Synroc produced by HIPing. Post-production thermal tests simulating the effects of a HLW glass pour in a surrounding canister have shown that the Synroc is stable and there is no exsolution of PuO₂ or CeO₂

[en] In 1987 samples of Pu²³⁸ and Cm²⁴⁴ doped Synroc C were prepared in the UKAEA Laboratories at Harwell. They were studied for five years before being archived. During decommissioning of the Harwell laboratories the samples were transferred to Sellafield and the opportunity was taken to conduct further studies. Given the age of the samples, they offer a unique insight into the long term radiation stability of Synroc. To date, the three Pu²³⁸ samples have been examined. The alpha decay dose experienced by the samples is estimated to be 3x10¹⁹ alphas per gram. The sample allowed to accumulate alpha decay damage (10587) was slightly heterogeneous, with an apparent grain size in the range 3-15μm. EDX analysis confirmed the phases present to be those expected in Synroc C and that the Pu had partitioned predominantly into the perovskite and zirconolite. Microcracking was observed in the hollandite and rutile but cracks arrested once they reached a zirconolite or perovskite grain. Sample 10588 was annealed after five years, at temperatures up to 1200 deg. C, this sample was micro-structurally similar to 10587 at the 20-50μm scale but differs at small scales. A major difference is the presence of both intergranular and intragranular porosity. Sample 10589 was annealed at the same time as 10588 but differed significantly probably due to actual fabrication temperatures being higher than those recorded. Information on these samples will be presented, along with a discussion of the implications for the expected long term stability of titanate ceramic waste-forms. (authors)

[en] The incorporation of Pu and Np in zirconolite (CaZrTi₂O₇) has been investigated over a range of redox conditions. Zirconolite formulations designed to favor either trivalent or tetravalent Pu and Np were prepared by limiting the amount of charge compensating additives available to maintain electroneutrality. From near-edge X-ray absorption spectroscopy the Pu valence state was found to vary with the processing atmosphere, from completely tetravalent when fired in air, and located on either the Ca or Zr sites, to trivalent, when substituted on the Ca site after annealing in 3.5% H₂/N₂. Np was predominantly tetravalent over the range of redox conditions examined and was readily incorporated on either of zirconolite''s Ca or Zr sites. The charge compensation mechanisms at work in different zirconolites are also discussed

[en] Three wt% each of Cs and Tc were mixed with the standard Synroc precursor and the ceramic was formed by hot-pressing. Attempts were made to incorporate the Tc as either metal or Tc⁴⁺, using different redox conditions in processing. Volatile losses of Tc during calcination were <0.1% in all cases. Short-term Tc leach rates when the Tc was present as a metal alloy were in the order of 10^-4 g/m²/d at 90 C with frequently changed water, and decreased with increasing leaching time. The valence of the Tc was monitored by X-ray absorption spectroscopy at the drying and calcination stages of the production. The general viability of Synroc/glass composites for immobilizing the Hanford HLW sludges is further demonstrated by using further refinements of additive schemes for the inactive ''''All-blend'''' formulation and initial studies using the U-containing All-blend waste formulation

[en] Synroc-C containing 10 wt% simulated PW-4b-D HLW including 0.62 wt% ²³⁹Pu was subjected to MCC-1 type leach tests at 70 C in deionized water, silicate and carbonate leachates for 53 d and deionized water for 2,472 d. The normalized total (i.e., unfiltered leachate + vessel wall) Pu leach rates in deionized water, silicate and carbonate leachates for periods up to 53 d were found to be of the order of 10^-5, 10^-4 and 10^-4 g/m² d respectively. After 2,472 d, the differential, normalized, Pu leach rate in deionized water dropped to ∼5 x 10^-6 (total) and ∼5 x 10^-8 (solution--after filtration through a 1,000 NMW filter) g/m²d. SEM and AEM were used to characterize the starting material and investigate the secondary phases on the surfaces of leached Synroc-C discs. Calculated and measured normalized Pu leach rates are compared and the partitioning of Pu between zirconolite and perovskite is discussed