The well-known effects of dissolved oxygen and hydrogen in respectively increasing and reducing the corrosion rate of zircaloys irradiated in high temperature water have been attributed to changes in the course of water radiolysis.1 Computer simulation of the growth and decay of radioly tic species produced by β, γ and neutron irradiation of water at 25°C and 305°C has been performed. In general, neutron irradiation leads to greater decomposition of water, and the effect of dissolved oxygen at 305°C is to markedly increase the concentrations of oxidizing radiolytic species. Correlation of zircaloy corrosion behaviour under such conditions with predictions of water radiolysis suggests that either HO2 of O− 2 are significant contributors to the corrosion enhancement phenomenon. Possible enhancement mechanisms are briefly discussed.

Water radiolysis and its effect upon in-reactor zircaloy corrosion

I have tried to summarize the oxidation behavior of zirconium and its alloys in both gaseous and aqueous environments, and to show how other environments, such as liquid metals, can be considered as special cases of one or other of the main classes. It will be appreciated from the extent of the literature on zirconium alloys (the over-600 references are by no means a complete bibliography) that it was impossible to discuss the details of many of the studies reported. To achieve a comprehensive survey in the space available it has been necessary to present a single coherent view of the field, without perhaps devoting sufficient space to opposing views and the evidence adduced in their favor. I have endeavored to make the references as comprehensive as possible, however, only omitting some early ones that are cited in later publications, which adequately summarized their contents. Readers who may be stimulated to pursue the details of any particular aspect of the field should have little difficulty tracing these other references from the bibliographies of the works that are cited. Finally, if the gaps in our knowledge, which I have attempted to illuminate, provide the inspiration for even one reader to devise experiments which can unambiguously resolve some of the many still unanswered questions, then I will consider this review to have been worthwhile.

Oxidation of Zirconium and its Alloys

/pdf/fenvironmental-degradation-of-structural-materials-in-liquid-1fk4kxqu.pdf

fEnvironmental degradation of structural materials in liquid lead- and lead-bismuth eutectic-cooled reactors

Oxide growth and dissolution on 316l stainless steel during irradiation in high temperature water

The effects of ionizing radiation on materials often reduce to "bad news." Radiation damage usually leads to detrimental effects such as embrittlement, accelerated creep, phase instability, and radiation-altered corrosion. This last point merits special attention. Elucidating synergies between radiation and corrosion has been one of the most challenging tasks impeding the deployment of advanced reactors, stemming from the combined effects of high temperature, corrosive coolants, and intense particle fluxes. Here we report that proton irradiation significantly and repeatably decelerates intergranular corrosion of Ni-Cr alloys in molten fluoride salt at 650C. We demonstrate this effect by showing that the depth of intergranular voids resulting from Cr leaching into the salt is reduced by the proton irradiation alone. Interstitial defects generated from proton irradiation result in radiation-enhanced diffusion, more rapidly replenishing corrosion-injected vacancies with alloy constituents, thus playing the crucial role in decelerating corrosion. Our results show that in industrially-relevant scenarios irradiation can have a positive impact, challenging our view that radiation damage always results in negative effects.

/pdf/proton-irradiation-decelerated-intergranular-corrosion-of-ni-58885sxtfe.pdf

P.A.J. McCullen

Papers

The effects of radiation on the corrosion of some Zr alloys