Corrosion of High Ni-Cr Alloys and Type 304L Stainless Steel in HNO sub 3 -Hf

摘要

Nineteen alloys were evaluated as possible materials of construction for steam heating coils, the dissolver vessel, and the off-gas system of proposed facilities to process thorium and uranium fuels. Commercially available alloys were found that are satisfactory for all applications. With thorium fuel, which requires HNO sub 3 -HF for dissolution, the best alloy for service at 130 exp 0 C when complexing agents for fluoride are used is Inconel 690; with no complexing agents at 130 exp 0 C, Inconel 671 is best. At 95 exp 0 C, six other alloys tested would be adequate: Haynes 25, Ferralium, Inconel 625, Type 304L stainless steel, Incoloy 825, and Haynes 20 (in order of decreasing preference); based on composition, six untested alloys would also be adequate. The ions most effective in reducing fluoride corrosion were the complexing agents Zr exp 4+ and Th exp 4+ ; Al exp 3+ was less effective. With uranium fuel, modestly priced Type 304L stainless steel is adequate. Corrosion will be most severe in HNO sub 3 -HF used occasionally for flushing and in solutions of HNO sub 3 and corrosion products (ferric and dichromate ions). HF corrosion can be minimized by complexing the fluoride ion and by passivation of the steel with strong nitric acid. Corrosion caused by corrosion products can be minimized by operating at lower temperatures. (ERA citation 05:032577)