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

6.37
are identical with those used for the risk analysis of other geologic waste disposal concepts
with the exception of possible bulk migration of the molten mass during the interim phase
between cavity sealing and solidification.
Ground Water Migration and Rock Melting. While a molten or high-temperature rock mass
would disrupt natural patterns of water movement in the vicinity of a repository, the rela-
tive effect would diminish with distance, until, at some point, the repository would have no
appreciable effect on water transport of radioactive materials. Presumably, if the hydrology
of the repository area were well characterized, its effects could be modeled by treating it
as a roughly spherical barrier with a radius that shrinks as the waste-rock matrix cools.
Preliminary work on a laboratory scale and at atmospheric pressure indicates that this "ther-
mal barrier" effect (Taylor 1977) could be demonstrated experimentally; however, additional
work that more closely simulates conditions expected at the repository depth would be
required.
Technological Issues
The technological issues that would require resolution before initiation of the rock
melting concept can be summarized as follows:
* The necessary geological information cannot be predicted with present knowledge.
* Empirical data on the waste/rock interaction and characteristics are lacking.
* No technical or engineering work design of the required facilities has been attempted.
It is not possible at this time to produce a design for the rock melt repository because the
necessary information is lacking. Data on the form and properties of the waste to be charged
into the cavity, the charging methodology, the properties of the host rock, and many techni-
cal aspects of the shaft sinking method and cavity construction technique would have to be
resolved. For many of these operations, work could not begin until fundamental waste/rock
properties are better known.
In addition, the concept would require operations and process activities that do not re-
adily lend themselves to the same degree of conservatism normally utilized in the nuclear
field. Discussed below are several areas that would require further scientific or technical
work.
Cavity Design and Construction. The greatest problem might lie in the construction of
the cavity. Although, it is within the bounds of current technology to lower men and equip-
ment through a 2-m-diameter shaft and construct the required cavity, such operations are dif-
ficult and time consuming. Methods for lining the cavity may have to be developed. Further-
more, it is practically impossible to construct the cavity without cracking the surrounding
rock. Since it may be necessary to maintain the waste inside the cavity for some years
before rock melting is permitted to begin, it would be necessary to ensure that waste does
not escape into the cracks and ultimately into ground water. It may be difficult to assure