The various methods for isolating toxic waste (chemical and radioactive) from the biosphere in stable geologic format10ns all require the host rock to be penetrated with boreholes, shafts, and/or tunnels, for exploration and access. The sealing of these penetrations is a significant consideration in acceptable waste isolation. This paper presents important design requirements and sealing concepts being developed. Further, quantative analyses to evaluate the effectiveness of sealing systems, the development of requirements for shaft and tunnel seals, and the development of basic requirements for sealing materials research have also been discussed.
The development of methods for safe disposal of toxic (chemical and radiological) wastes is a continuing concern throughout the world. Isolating the waste from the biosphere by confining it in deep stable geologic formations.is currently being considered as technically attractive and feasible disposal method. Such isolation necessarily requires that the host and overburden media be penetrated with boreholes, shafts and/or tunnels for exploration and access. If not properly sealed, these penetrations can represent unacceptable pathways to the biosphere, and hence their sealing is a significant consideration in waste disposal. This paper represents a progress report on the current sealing design studies being performed by D'Appolonia, under a contract with Battelle Memorial Institute, the Office of Nuclear Waste Isolation (ONWI). ONWI has the overall responsibility for the technical program management of the U. S. National Waste Terminal Storage Program sponsored by the U. S. Department of Energy. As a part of the effort in this program it is responsible for the development and verification of sealing techniques for future repositories in all types of host rocks. This paper in the following sections presents the design goal, considerations in development of seal designs, preliminary analysis of borehole plugs, materials research and differences in sealing shafts/tunnels and plugging boreholes. Before proceeding further, a brief discussion of differences in disposal of radioactive and chemical wastes is in order. Radioactive wastes decay with time and thus at some time in the future their toxicity may reduce substantially. Chemical wastes will not necessarily decay with tune except for any chemical and biological activity. Thus, for isolation of radioactive wastes the tune of isolation is a helpful consideration, whereas in chemical waste disposal, the time mayor may not be an ally. At the present time the most significant technical efforts in waste isolation have been directed towards radioactive wastes, thus, the sealing design developments discussed are for radioactive wastes, however, the basic concepts are also valid for chemical wastes.
The fundamental goal of any repository and its seals is to prevent a release of the waste of such magnitude as to present a hazard to the biosphere. Four alternate design goals which were considered (Shukla, et. al, 1980) and evaluated, varied from "returning the repository formation to its original permeability" to "providing seals which control releases to an acceptable level through restriction of flow and absorption of the waste product in the seal zone". The recommended qualitative design goal is as follows: