B4C ZIRCALOY REACTION AT TEMPERATURES FROM 1,173-K TO 1,953-K/

With a view to obtaining the basic information on the influence of the BWR type control rod failure on the bundle degradation during a sever e accident, the chemical interactions between B4C neutron absorber mat erial and Zircaloy were investigated in the temperature range 1,173 to 1,953 K. Reaction layers were formed at the interface between two mat erials. Growth of the reaction layer and decrease in the Zircaloy thic kness were measured as a function of temperature and time, thereby the reaction kinetics was evaluated. The overall reaction generally obeye d a parabolic rate law and the reaction rate constant at each examined temperature was determined. A sudden increase of the reaction rate wa s found at a temperature between 1,823 and 1,873 K. It could be caused by liquid phase formation of the zirconium-boron carbide system at th e corresponding temperature, which occurred locally at the reaction fr ont. Accordingly, the temperature dependence of the reaction rate cons tants was estimated separately for the two temperature ranges of 1,173 to 1,823 K and 1,873 to 1,953 K.