22 - Radioactive Waste Disposal

Abstract

This chapter discusses radioactive waste disposal. Materials that contain radioactive atoms and that are deemed to be of no value are classed as radioactive wastes. They may be natural substances such as uranium ore residues with isotopes of radium and radon or products of neutron capture with isotopes such as those of cobalt and plutonium, or fission products with a great variety of radionuclides. Wastes may be generated as by-products of national defense efforts, of the operation of commercial electric power plants and their supporting fuel cycle, or of research and medical application at various institutions. The radioactive components of the waste may emit alpha particles, beta particles, gamma rays, and neutrons in some cases, with half-lives of concern from the standpoint of storage and disposal ranging from several days to thousands of years. For purposes of management and regulation, a classification scheme for radioactive wastes has evolved. The original wastes were from the Hanford reactors, used in World War II to produce weapons material. The wastes were stored in moist form in large underground tanks. The management of spent fuel at a reactor involves a great deal of care in mechanical handling to avoid physical damage to the assemblies and to minimize exposure of personnel to radiation. At the end of a typical operating period of one year for a PWR, the head of the reactor vessel is removed and set aside. The whole space above the vessel is filled with borated water to allow fuel assemblies to be removed while immersed. Low-level wastes come from research and medical procedures and from a variety of activation and fission sources at a reactor site. They generally can be given near-surface burial. Isotopes of special interest are cobalt-60 and cesium-137.