The Isolation of High-Level Nuclear Wastes in a Geologic Repository

Abstract

Options seriously considered for isolation of high-level nuclear wastes that involve geologic media differ primarily in emplacement technique and location. Of these options, emplacement in a deep, excavated cavity, or geologic repository, is the currently favored method. The most likely means of returning radionuclides from a sealed geologic repository to the biosphere is by dissolution and transport of these by ground water. The potential hazard from deeply buried radionuclides therefore depends primarily upon three important apsects: the amount and rate of supply of radionuclides to the groundwater; the pathways and rate of groundwater movement; and the degree of geochemical retardation imposed by the geologic media. The assessment of sites possibly suitable for a geologic repository must involve a critical evaluation of: (1) the performance of the existing geologic system; (2) the probable future performance of the natural system, taking into consideration evolutionary change and potentially disruptive events; and (3) the disturbance to the natural system caused by excavation, waste emplacement, sealing, and the presence thereafter of the waste facility. The assessment of risk is possible only if reasonable predictions can be made regarding the repository environment. Because actual tests and demonstrations of repository system behavior cannot be conducted under various changing conditions over representative periods of time, mathematical models must be used to predict the long-term behavior of the system. Many individuals have concluded that nuclear power must be a major contributor to our energy needs in the immediate future if we are to maintain an acceptable energy economy. Along with the benefits of nuclear energy comes a penalty, however: we must dispose of the hazardous wastes generated by nuclear reactors. No reasonable person would advocate the expansion of nuclear energy if a safe means of nuclear waste disposal did not exist. Although several types of wastes are produced, the high-level wastes are of greatest concern to most individuals because virtually all of the radioactivity is in the high-level waste. In point of fact, the volume of this waste is relatively insignificant compared with that of other wastes generated, but a question weighing heavily on the public's mind is, What alternatives are there for the safe disposal of this waste? One could imagine total disposal schemes such as ejection from the earth by rocket or elimination by burning the radionuclides in nuclear reactors. The efficacy of any such technique depends not only upon finding a satisfactory scheme ' This paper is based on a presentation given at the Radiation Research Society Plenary Session,