Chapter 10 - Long-Term Core Behavior

Abstract

This chapter addresses the long-term changes that occur over the lifetime of a power reactor core. These changes are most directly tied to the evolution of the fuel composition and its by-products as a function of time. They fall into three categories namely the buildup and decay of radioactive products of fission, fuel depletion, and the buildup of actinides resulting from neutron capture in fissile and fertile materials. These phenomena take place on time scales that are substantially long. Whereas fission products have half-lives from seconds to decades, many such as xenon and samarium, have half-lives of several hours or more. The effects of fuel depletion are measured on yet longer time scales, typically weeks, months, or years. The chapter explains the process of xenon poisoning which is the exceedingly large absorption cross section of the isotope xenon-135, resulting in the most substantial fission product effects on reactor operation. The chapter also explains in detail the topics of fission product buildup and decay, fuel depletion, and the fission product and actinide inventories.