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Understanding the association and retention of tritium in metals has significance in nuclear decommissioning programs and can lead to cost benefits through waste reduction and recycling of materials. To develop insights, a range of metals from two nuclear sites and one non-nuclear site were investigated which had different exposure histories. Tritium speciation in metals was inferred through incremental heating experiments over the range of 20-900 °C using a Raddec Pyrolyser instrument. Systematic differences in thermal desorption profiles were found for nonirradiated and irradiated metals. In nonirradiated metals (e.g., stainless steel and copper), it was found that significant tritium had become incorporated following prolonged exposure to tritiated water vapor (HTO) or tritium/hydrogen gas (HT) in nuclear facilities. This externally derived tritium enters metals by diffusion with a rate controlled by the metal composition and whether the surface of the metal had been sealed or coated prior to exposure. The tritium is normally trapped in hydrated oxides lying along grain boundaries. In irradiated metals, an additional type of tritium can form internally through neutron capture reactions. The amount formed depends on the concentration and distribution of trace lithium and boron in the metal as well as the integrated neutron flux. Liberating this kind of tritium typically requires temperatures above 800 °C. The pattern of tritium evolution derived from simple thermal desorption experiments allows reliable inferences to be drawn on the likely origin, location, and phases that trap tritium. Any weakly bound tritium liberated at temperatures of ~100 °C is indicative of mostly HTO interactions in the metal. Any strongly bound tritium liberated over the range of 600-900 °C is indicative of neutrogenic tritium formed via neutron capture by trace Li and B. Neutron capture by lithium is likely to be more significant than for boron based on lithium's higher trace element abundance and neutron cross section. The time required for efficient thermal desorption of tritium ultimately depends on the metal composition, its tritium exposure history, integrated neutron flux, sample size, sample geometry, heating rate, and final desorption temperature.

Large volumes of potentially tritium-contaminated waste materials are generated during nuclear decommissioning that require accurate characterisation prior to final waste sentencing. The practice of initially determining a radionuclide waste fingerprint for materials from an operational area is often used to save time and money but tritium cannot be included because of its tendency to be chemically mobile. This mobility demands a specific measurement for tritium and also poses a challenge in terms of sampling, storage and reliable analysis. This study shows that the extent of any tritium redistribution during storage will depend on its form or speciation and the physical conditions of storage. Any weakly or moderately bound tritium (e.g. adsorbed water, waters of hydration or crystallisation) may be variably lost at temperatures over the range 100-300 °C whereas for more strongly bound tritium (e.g. chemically bound or held in mineral lattices) the liberation temperature can be delayed up to 800 °C. For tritium that is weakly held the emanation behaviour at different temperatures becomes particularly important. The degree of (3)H loss and cross-contamination that can arise after sampling and before analysis can be reduced by appropriate storage. Storing samples in vapour tight containers at the point of sampling, the use of triple enclosures, segregating high activity samples and using a freezer all lead to good analytical practice., (Copyright © 2012 Elsevier B.V. All rights reserved.)