In the post-closure period of a deep disposal facility for lowand intermediate-level radioactive waste, pore-fluids chemically equilibrated with cementitious components of the engineered barriers will migrate into the surroundings. Secondary calcium silicate hydrate (CSH) phases might be formed in the micro pore system of the rocks and change the available porosity for radionuclides and hence permeability. Since the retardation of radionuclides in host rock is dependent on the sorption and matrix diffusion, these chemical reactions are of concern. Experiments have been undertaken to react discs of Äspö diorite with alkaline cement porewaters. These experiments provided aged material for through diffusion experiments and samples for studies of chemical reactions. 1 cm thick discs of Äspö diorite were reacted with waters representative for fresh and leached concrete at 70 °C in nitrogen filled vessels for six months. Analysis of the waters indicates dissolution of primary minerals and precipitation of secondary CSH phases. HTO, Na and Cs diffusion experiments were then undertaken with both reacted and unreacted discs in a nitrogen-flushed glovebox facility. The effects of alkaline degradation of Äspö diorite on tracer through-diffusion was found to be small and of the same order of magnitude as natural variations in rock heterogenity between undegraded samples. feet on the diffusivities and sorption characteristics of the rock. Previous experimental studies of the reaction of common rock-forming minerals with Ca(OH) 2 saturated fluids and mixed Na-K-Ca-OH fluids [1, 2] have used temperatures of up to 70 °C to increase the degree of reaction whilst not favouring unrepresentative secondary reaction products. A range of calcium (aluminium) silicate hydrate (C(A)SH) phases and hydrogarnet were precipitated. However, these studies generally used granular material. Although useful for understanding reaction mechanisms, the samples were not large enough to be used in diffusion studies. The crushing of the mineral will also create new surfaces with properties that may be unrepresentative of the inner surfaces of the original material. The work presented here investigated the reactions of discs of Äspö diorite with synthetic cement porewaters. The experiments were designed as a preliminary investigation into how secondary precipitates would change diffusion properties of the Äspö diorite. After ageing in the alkaline solutions, half the discs were compared with unaged discs in diffusion measurements. The remainder of the discs were used for mineralogical studies.

Two Waste Encapsulation and Storage Facility (WESF) " ' C s capsules have been analyzed destructively after five years of service in the Sandia Irradiator for Dried Sewage Solids (SIDSS). Analysis of these capsules was a joint undertaking of Sandia National Laboratories Albuquerque (SNLA) and Battelle Pacific Northwest Laboratory (PNL) with assistance from Rockwell Hanford Operations (R H O). The program concentrated on studies of the inner capsule, inner capsule weld areas, and analysis of the CsCl salt. No measurable corrosion was observed on the capsule wall or welds after the five years in the SIDSS Facility. The operating temperatures of the inner capsule wall were calculated to be between 140° and 18OOC. Radiochemistry and isotopic analyses provided data for specific activity calculations. There was good correlation between the measured calorimetry of the capsules before sectioning, 53 and 55 kCi, and the activity calculations, 5 4 and 59 kCi, respectively.

No abstract