Fission product release during LWR loss-of-coolant accidents

Experiments performed at Oak Ridge National Laboratory with fission product simulants and with irradiated light water reactor (LWR) fuel have been employed to develop semiempirical models of fission product release from defected LWR fuel rods. At fuel temperatures less than 1200/sup 0/C, releases of semivolatile species are postulated to result from two mechanisms. The first of these, a burst release mechanism, is due to the transport of the fill and fission product gases as they are vented through the cladding defect. The second mode, diffusional release, is described as the migration of the fission products through the interconnected voids (e.g., the fuel-cladding gap) due to ordinary gas-phase diffusion. The two mechanisms are further assumed to be additive. Releases calculated by these models are presented.