Abstract
ABSTRACTThe potential14C (carbon-14, radiocarbon) flux from disposal of14C containing waste into air is compared with the natural14C emanation rate from soil in order to put the14C hazard potential from disposal of this waste in perspective with the14C exposure from cosmogenic origin. Chemical corrosion of neutron irradiated metals, steel and Zircaloy, is bounded by diffusion of water through a thermodynamically stable metal-oxide layer and dissolution of this metal-oxide in a nuclear plant. Many countries process radioactive waste for disposal using cementitious materials, an acknowledged end-point management technique for this waste. The metal-oxides are also stable when these waste forms are embedded in cementitious materials. The14C release rate from this Zircaloy at these alkaline and reducing conditions is comparable to the natural14C emanation rate from soil into air. Neutron irradiated graphite and spent ion exchange resins are chemically inert and therefore other release mechanisms need to be assumed. Radiolytic corrosion is used to determine the14C release rate from this graphite. Moreover, ion exchange—with ingressing anionic species that have a higher affinity than contained anionic14C—is proposed as a release mechanism for these resins.
Highlights
The EC Carbon-14 Source Term (CAST) project aimed to develop understanding of the potential release mechanisms of 14C containing waste under conditions relevant for waste packaging and disposal to underground geological disposal facilities
The irradiated metals and spent ion exchange resins are frequently processed with cementitious materials and the 14C release from these four waste forms has been investigated at chemical representative conditions in CAST
These are 1.08–1.35 × 105 Bq/g solid matter for neutron irradiated graphite from Vandellós I, a graphite gas cooled reactor in Spain (Toulhoat 2018) and a value of 2.7 × 105 Bq/g solid matter for a stainless steel plenum spring, neutron irradiated in the Gösgen Pressurized Water Reactor (PWR) in Switzerland (Herm 2017; Mibus 2018)
Summary
The EC Carbon-14 Source Term (CAST) project aimed to develop understanding of the potential release mechanisms of 14C (carbon-14, radiocarbon) containing waste under conditions relevant for waste packaging and disposal to underground geological disposal facilities. The irradiated metals and spent ion exchange resins are frequently processed with cementitious materials and the 14C release from these four waste forms has been investigated at chemical representative conditions in CAST. At alkaline reducing conditions, dissolved organic carbon compounds have been measured to be the major 14C species released from neutron irradiated steel, except for specimens with the highest calculated 14C activity concentrations (Mibus 2018), neutron irradiated Zircaloy (Necib 2018) and neutron irradiated graphite (Toulhoat 2018).
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