Radioactive species that enter the coolant stream of a gas-cooled reactor are carried in the stream and deposited on coolant passages and various system components. Analytical relations are presented for deposition of radioactive particles from isothermal gas streams to the walls of a conduit as a function of time, distance, and variable source release rate. Effect of recirculation of the coolant gas on deposition is also included in the analysis. In the physical model considered, particles are assumed to be transported from the gas stream to the immediate vicinity of the walls of the conduit by diffusion; the resistance to mass transfer by diffusion is obtained by analogy from heat transfer coefficients. At the wall surface an imperfect retention scheme is assumed, that is particles striking the wall surface are not all deposited but some re-enters the gas stream. This imperfect retention scheme is characterized by a wall surface resistance to mass transfer in series with the stream resistance to mass diffusion. To simplify the presentation of the analysis this unknown wall surface resistance has been incorporated into a single factor, P, which enters the equations as a multiplier to the stream mass transfer coefficient. The analysis is correlated with experiments for deposition of fission products from isothermal helium streams on the surface of a stainless steel tube.

The Three Mile Island and Chernobyl nuclear incidents emphasized the need for the world-wide nuclear community to cooperate further and exchange the results of research in this field in the most open and effective manner. Recognizing the roles of heat and mass transfer in all aspects of fission-product behavior in sever reactor accidents, the Executive Committee of the International Centre for Heat and Mass Transfer organized a Seminar on Fission Product Transport Processes in Reactor Accidents. This book contains the eleven of the lectures and all the papers presented at the seminar along with four invited papers that were not presented and a summary of the closing session.