FISSION-PRODUCT DEPOSITION AND ITS ENHANCEMENT UNDER REACTOR ACCIDENT CONDITIONS:DEPOSITION ON PRIMARY-SYSTEM SURFACES One of Three Separate Final Reports on Task 3

摘要

Iodine deposition on prefilmed Zircaloy and stainless steel surfaces and tellurium deposition and desorption on bare and prefilmed Zircaloy surfaces were studied as related to fission-product behavior in the primary vessel during a loss-of-coolant accident in a water-cooled reactor. Iodine deposition experiments were conducted with l2-air-steam and Hl-hydrogen-steam over the temperature range 150 to 750 C. Tellurium deposition and desorption experiments were conducted at 200 to 500 C.nIodine deposition rates were extremely low and decreased with increasing temperature according to an Arrhenius relationship. Rate coefficients of the order of 10-2 to 10~3 cm per sec for EI and 10~3 to 10-5 cm per sec forI2% were determined over the temperature range 150 to 750 C. The deposition coefficients for I2 were first order while those for EI exhibited a dependency upon square root of time and square root of HI concentration. Because of the corrosive action of iodine, deposition was greater on bare metal surfaces than on prefilmed surfaces, and any effects of stress on iodine deposition were limited to the extent that the oxide film was cracked and bare metal was exposed. Application of the experimental deposition data to loss-of-coolant accident conditions indicates that little I2 or EI would be deposited on primary-system surfaces.