Study on Target wastage for Sodium-water Reaction Environment Formed on Periphery of Adjacent Tube in Steam Generator of Sodium-cooled Fast Reactor　Composite Oxidation-Type Corrosion with Flow Experiment using High-temperature Sodium Hydroxide

Abstract

A sodium-water reaction (SWR) would take place in the case of a breach of the heat transfer tube in the steam generator (SG) of a sodium-cooled fast reactor (SFR) , and the reaction jet may cause wear to the neighboring tubes by thermal and chemical effects, which is so-called target wastage. Accordingly, failure propagation caused by target wastage may potentially reduce the secondary cooling system integrity. In a previous study, a great number of experiments on target wastage were carried out for candidate materials under practical SG operation conditions. The target wastage rate for cited materials was derived from macroscopic boundary factors of the reaction jet. However, this mock-up approach is not versatile and is not suitable for large-scale SG design. Therefore, target wastage should be focused on for the safety assessment of various SG designs. In this study, experimental apparatus and a technique for producing composite oxidation-type corrosion with flow (COCF) , which is an integral part of target wastage, were developed to determine the separation effect of local wastage factors under the high-temperature sodium hydroxide (NaOH) and sodium monoxide (Na 2 O) environment mainly generated by the SWR. The authors quantitatively evaluated the effect of the material temperature and fluid velocity on the COCF rate. It was revealed that COCF produced sodium-iron composite oxidation-type corrosion from metallographic observation and element assay.