Material Analysis and Radioisotope Studies of Spent Nuclear Fuel found in the Marine Environment
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Material Analysis and Radioisotope Studies of Spent Nuclear Fuel found in the Marine Environment I.D. Baikie1, Frank Dennis, Ron Crawford and Massimo Scirea UKAEA, Dounreay, Thurso, KW14 7TZ, UK 1 KP Technology Ltd, Milton House, Thurso Road, Wick Caithness, KW1 5LE, UK ABSTRACT Sand-sized particles of spent nuclear fuel have been found in the environment at Dounreay, north Scotland. These particles, believed to have been discharged during early stages of site operations in the 1960s, have been recovered from areas within the Site, coastal foreshore adjacent to the Site and offshore (marine) environments. As part of the Dounreay Site Restoration Plan, a significant program of work is being undertaken to establish the fate of the Dounreay particles in the marine environment. This program includes materials analysis of particles and particle analogues The diverse depositional environments, coupled to relatively long fuel-particle residence times, allow insight to be gained into the behaviour of the particles in the natural environment. This includes the effects of physical, chemical and mechanical processes such as particle erosion and corrosion, particle abrasion and particle-saltwater interaction. Using materials analysis techniques including Scanning Electron Microscopy, Energy Dispersive X-Ray Analysis, Electron Probe Microanalysis, together with 137Cs activity measurement we review the fuelparticle mechanical and chemical stability and current radio-isotope composition. These studies allows us to identify the fuel provenance, fuel treatment history and draw some general conclusions of the ultimate fuel particle residence time. We demonstrate that radioisotope modelling strongly indicates that particle break-up is limited by the chemical effects of the marine environment coupled with the native oxide films present on the metallic fuel. Particle transport and distribution are governed by environmental effects on the sediment and sediment transport mechanisms such as tidal currents and storm events. This study is unique in that it involves the potential effects of long-term saltwater and abrasion interactions with fuel matrixes containing both U-Al and U-Mo of which there is little literature available. INTRODUCTION To date 1045 particles containing spent nuclear fuel have been recovered from the Dounreay site, coastal foreshore and the offshore marine environment adjacent [1]. The offshore cohort constitute the majority (74%) of particle finds. Gamma-ray spectroscopy of the caesium (Cs) isotopic content of some 20 particles suggests that the cooling time is (38 ± 3) years, indicating that they have been irradiated about 1966 [2]. The current knowledge of the particle discharge pathways indicates that the most likely route was through a low active drain which discharged effluent to the sea via a diffusion chamber 23 m beneath the seabed, some 600 m offshore. Materials analysis of a number of these particles [3-5] indicate that most of them are derived from two types of irradiated fuel: Materials Test Reacto
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