The effect of thermal diffusion from fuel pellets on rewetting of overheated water reactor pins

This paper presents the results of a finite difference solution of a conduction equation for the rewetting of a hot tube containing a filler material. The results show that the effect of a filler is always to reduce the rewetting velocity compared with an empty tube and reasonable agreement is obtained with previous experimental work. The effects of a gas gap on the rewetting of a UO₂-filled Zircaloy tube are discussed. A simple physical model is also presented which shows that the dominant parameter in determining the effect of a filler is (kpc)^1/2. It is suggested that previous theories for rewetting rate derived for empty tubes can be modified to include the effects of a filler by the use of a conduction correction term.