Management of Commercially Generated Radioactive Waste - U.S. ...

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to shallow ground water or to the surface for an extended time period. Expansive concretes
make the best seals under current technology and do so at an acceptable cost. However,
current experience with seals, whether of cement, chemical, or of other materials, is only a
few years old. Further development of sealing technology would, therefore, be required
(Bechtel 1979a). For integrity to be maintained, the sealing material would have to meet the
following requirements:
* Chemical composition - the material must not deteriorate with time or temperature when
compared to host rock characterization.
* Strength and stress-strain properties - the seal must be compatible with the surrounding
material, either rock or casing.
* Volumetric behavior - volume changes with changes in temperature must be compatible with
those of enclosing medium.
The sealing system for well injection would consist not only of plugs within the casing,
but also of material to bridge the gap between casing and competent rock not damaged by dril-
ling. To minimize possible breaks in containment, rigorous quality assurance would be re-
quired during emplacement of several high quality seals at strategic locations within the
borehole.
Research and development would be needed in two major areas - material development and
emplacement methodology - to ensure complete isolation. Material development would include
investigating plugging materials (including special cements), compatible casing materials,
and drilling fluids. Because the seal would include the host rock, these investigations
should include matching of plugging materials with the possible rock types. It is conceiv-
able that different materials would be required at different levels in the same hole.
Emplacement methodology would have to be developed for the environment of the hole. Con-
siderations would include operation in the aqueous environment, casing and/or drilling, and
fluid removal. Because the emplacement methodology would depend on the type of material,
initial studies of material development would have to precede emplacement methodology devel-
opment. However, the two investigations would be closely related and would interface
closely. In situ tests would have to be performed to evaluate plugging materials. Equipment
developed would include quality control and quality assurance instrumentation.
Monitoring Techniques. In common with other methods of underground disposal, techniques
would be required for monitoring the movement/migration of radioactive material from the
point of emplacement.
Borehole Plugging Techniques. Borehole plugging techniques would require development at
an early stage to permit safe exploration of candidate sites.
Implementation Time and Estimated R&D Costs
The R&D program described above is generic. Specific estimates for required implementa-
tion time and R&D costs would depend on the details of the actual development plan, and are
deferred pending plan definition.