Development of the residual sodium quantification method for a fuel assembly of SFRs

In a fuel handling system of sodium-cooled fast reactors (SFRs), it is necessary to remove the sodium remaining on spent fuel assemblies (FAs) before storing them in a spent fuel water pool (SFP). A next-generation SFR in Japan has adopted an advanced dry cleaning process which consists of argon gas blowing to remove the metallic residual sodium on the FA, which increases economic competitiveness and reduces waste products thanks to a waterless process. In this R&D work, performance of the dry cleaning process has been investigated. This paper describes experimental and analytical work focusing on the amount of residual sodium remaining on FA components, for instance the handling head, the wrapper tube, the upper shielding, and the entrance nozzle. The tests, using water and sodium, investigated the amount of residual liquid remaining on laboratory scale specimens representing three fundamental shapes: narrow gaps, horizontal holes, and corners. On the basis of the experimental results, the residual sodium quantification method for FA was constructed. The constructed method enables quantitative estimation of the amount of residual sodium on the entire FA before and after the argon gas blowing with 95% reliability. (author)