Using thermal evolution profiles to infer tritium speciation in nuclear site metals: an aid to decommissioning
Using thermal evolution profiles to infer tritium speciation in nuclear site metals: an aid to decommissioning
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.
9177-9185
Croudace, Ian W.
24deb068-d096-485e-8a23-a32b7a68afaf
Warwick, Phil E.
f2675d83-eee2-40c5-b53d-fbe437f401ef
Kim, Daeji
06902d3d-1389-4cd7-8b78-db8459d81378
16 September 2014
Croudace, Ian W.
24deb068-d096-485e-8a23-a32b7a68afaf
Warwick, Phil E.
f2675d83-eee2-40c5-b53d-fbe437f401ef
Kim, Daeji
06902d3d-1389-4cd7-8b78-db8459d81378
Croudace, Ian W., Warwick, Phil E. and Kim, Daeji
(2014)
Using thermal evolution profiles to infer tritium speciation in nuclear site metals: an aid to decommissioning.
Analytical Chemistry, 86 (18), .
(doi:10.1021/ac502244a).
Abstract
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.
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Accepted/In Press date: 26 August 2014
e-pub ahead of print date: 26 August 2014
Published date: 16 September 2014
Organisations:
Geochemistry
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Local EPrints ID: 369839
URI: http://eprints.soton.ac.uk/id/eprint/369839
ISSN: 0003-2700
PURE UUID: fd9927b2-ca26-4819-a917-d9825224888c
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Date deposited: 07 Oct 2014 13:29
Last modified: 15 Mar 2024 02:49
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Daeji Kim
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