Chemical aspects of dual environment corrosion by molten lead and cesium molybdate on 15-15Ti cladding tube

15–15Ti stainless steel is one of the prime candidates for cladding and structural materials to be used in Lead-cooled Generation-IV reactors. Currently, the corrosion process of 15–15Ti at elevated temperatures (≥600 °C) is lacking data and more research is needed. Moreover, corrosion research on this field has been focused on the molten lead side, while the fission product (selected as cesium molybdate here) has not received enough attention. In this study, 15–15Ti cladding tube was exposed to molten lead on the outer side, and cesium molybdate on the inner side, aiming to create a dual environment corrosion scenario close to the one present in operation. Severe oxide scale delamination caused by molten lead was identified forming repeated layers of molten lead and iron-oxide. Deeper into the alloy, molten lead has caused spinel type internal oxidation scales, where iron-chromium spinels were seen as intergranular attack, increasing severity with the temperature. Cesium molybdate corrosion was found to cause a similar spinel oxide formation. Diffractograms obtained on complementary coupon experiments were used to differentiate spinel and corundum type oxide scales. Comparing the severity of corrosion by molten lead with that caused by cesium molybdate, it has been molten lead causing significant higher material loss by delamination at all investigated temperatures.