METHOD FOR DESCRIBING THE ZIRCALOY-4 OXIDATION USING THE ANALYTICAL SOLUTION OF THE OXYGEN DIFFUSION EQUATION

The oxidation of the Zircaloy-4 fuel element sheath at high temperatur e transients is treated as a moving boundary one-dimensional diffusion problem. It is usually served by numerical methods. A method is provi ded in this work to analytically solve the oxygen diffusion equations. The temperature transient has been approximated as a stepwise functio n of time, {T-i, (t(0i), t(i))}i=1,n. The main assumption was that in the beginning of the ith step of the temperature transient the oxide g rown during the previous steps, x(0i), could be considered as being fo rmed at a constant temperature, T-i, but during another time interval, named equivalent time interval Delta t(eq). Calculations have been ma de with a routine, OXCON, developed using this model. The results appr oach well the predictions of validated corrosion codes, FROM and PRECI P-II, which solve the diffusion equations using numerical methods.