Oxidation characteristics of lead-alloy coolants in air ingress accident

The chemical behaviors of lead (Pb) based coolants in the air ingress accident of fast reactors were investigated by means of the thermodynamic considerations and the static oxidation experiments for Pb alloys at various chemical compositions. The results of the static oxidation tests for lead-bismuth (Pb-Bi) alloys indicated that Pb was depleted from the alloy due to the preferential formation of PbO in air at 773K. Bi was not involved in this oxidation procedure. Pb-Bi oxide and Bi2O3 were formed after the enrichment of Bi in the alloys due to the Pb depletion. The thickness of the oxide layer formed on liquid LBE at static condition was approximately 1mm. The oxidation rates of the alloys were much larger than that of the steels, and became larger with higher Pb concentration in the alloys. The compatibility of Pb-Bi alloys with stainless steel was worse when the Pb concentration in the alloys became low, since the dissolution type corrosion was promoted by the Bi composition in the alloy. The Pb-Li alloys were oxidized as they formed Li2PbO3 and Li2CO3. Then, Li was depleted from the alloy. These oxides of the coolant can be generated in the low temperature region of the reactor system after the increase of oxygen concentration in the coolant system in the air ingress accident.