A scoping study on debris bed formation from metallic melt coolant interactions

Abstract

During a hypothetical severe accident in a light water reactor, the core and internal structures melt down and the molten materials (corium) may fall into a water pool, forming a debris bed from so-called fuel coolant interactions (FCI), whose characteristics are important to corium coolability. The present study is concerned with the characterization of an ex-vessel debris bed forming form the FCI of a metal rich corium jet falling into a water pool in the reactor cavity. Five scoping tests were carried out on the DEFOR-M test facility using metallic Tin melt at different superheats. The molten tin was employed as the simulant of metal (Zr/Fe) rich corium melt. The processes of melt jet fragmentation and debris formation was recorded by high-speed cameras. The contour and volume of the resulting debris bed were measured by a three-dimensional laser scanning system, and the debris particles were sieved for their size distribution. The experimental results revealed the effects of melt superheat and water subcooling on the characteristics of a debris bed, including the bed’s configuration and porosity, the particles’ morphology and size distribution. A preliminary comparison of debris bed characteristics between metallic melt and oxidic melt was also provided.