One of the main challenges for the nuclear power industry today is the disposal of spent nuclear fuel. One of the most developed methods for its long term storage is the Swedish KBS-3 concept where the spent fuel is sealed inside copper canisters and placed 500 meters down in the bedrock. Gamma radiation will penetrate the canisters and be absorbed by groundwater thereby creating oxidative radiolysis products such as hydrogen peroxide (H2O2) and hydroxyl radicals (HO˙). Both H2O2 and HO˙ are able to initiate corrosion of the copper canisters. In this work the kinetics and mechanism of reactions between the stable radiolysis product, H2O2, and copper and copper oxides were studied. Also the dissolution of copper into solution after reaction with H2O2 was monitored by ICP-OES. The experiments show that both H2O2 and HO˙ are present in the systems with copper and copper oxides. Nevertheless, these species do not appear to influence the dissolution of copper to the same extent as observed in recent studies in irradiated systems. This strongly suggests that aqueous radiolysis can only account for a very minor part of the observed radiation induced corrosion of copper.
The effect of gamma radiation on corrosion of copper under anoxic conditions in pure water has been studied experimentally. Copper samples submerged in water were exposed to dose rates of 0.37 or 0.77 kGy/h. Reference samples were used throughout. The copper surfaces have been examined using the techniques of SEM-EDS, IRAS, CR spectroscopy and AFM. Dissolution of copper was measured using ICP-OES. The results show that irradiated samples are more corroded than corresponding reference samples. This is also reflected by the increased concentration of copper in water after irradiation. Surface examination also reveals local corrosion features.
The influence of a pregrown copper
oxide layer on radiation-induced
corrosion of polished copper in pure anoxic water has been explored.
The resulting amount of copper oxide formed during corrosion was measured
with cathodic reduction, and the concentration of dissolved copper
in solution was measured with inductively coupled plasma atomic emission
spectroscopy. The identity of corrosion products and their topography
was determined with Raman spectroscopy and scanning electron microscopy,
respectively. Nonirradiated reference samples were analyzed for comparison.
The results show that radiation-induced corrosion of copper in anoxic
water is significantly more effective on preoxidized copper compared
to polished copper. The total amount of oxidized copper exceeds the
amount expected solely from radiation chemistry of water by more than
3 orders of magnitude. To explain this discrepancy a mechanism is
suggested where the hydroxyl radical (HO·) is the main radiolytic
oxidative species driving the corrosion process. If the thermodynamic
driving force would be large enough (such as for the hydroxyl radical
or its precursor, H2O+), the oxide layer could
conduct electrons from the metal to the hydroxyl radicals formed at
oxide surfaces. The formation of an oxide layer will then result in
an increased reactive surface area partly accounting for the observed
discrepancy.
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