ABSTRACT
Particle transport during reactor loss-of-coolant accidents (LOCAs) occurs as the result of two distinct processes called advection and diffusion. This chapter discusses how these processes effect the dispersion of radioactive particles produced by a hypothetical reactor accident. It also discusses how these particles are dispersed if they happen to escape the containment building entirely. Advection is the dominant form of mass and energy transfer in nuclear power plants, and this is particularly true during reactor accidents and LOCAs. Energy transport during diffusion occurs at a molecular level, while energy transport during advection occurs because of the macroscopic or bulk motion of the material. In addition to diffusion and advection, which apply to relatively small particles, larger radioactive particles can also be transported by a moving fluid. In addition to drag forces that are exerted on a particle by a fluid, a buoyancy force may also be exerted on the same particle.
