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

6.25
evaluated only on the basis of site-specific parameters. The lack of specific data prevents
a quantitative evaluation. However, it is not expected that resulting impacts would be any
greater than those for a mined geologic repository under comparable conditions and might be
less due to the longer pathway of smaller diameter than a mine shaft.
Natural Phenomena. Another concern for the VDH concept in the long term would be the
susceptibility of the ground-water system to tectonic changes and volcanic action. The very
concept of the deep hole is aimed at minimizing such effects by increasing the distance to
the biosphere as much as is technically feasible. Placement of the waste disposal site in a
tectonically stable region would reduce the probability of such catastrophic events. Site-
specific data would be required to quantitatively assess the impact of natural phenomena
leading to degradation of the containment.
Inadvertent Human Encroachment. Human intrusions into the VDH repository in the long
term could result from drilling, exploration, and excavations. Monitoring, surveillance, and
security operations carried out after the repository were closed would provide an increment
of safety against such occurrence. However, the physical depth of the VDH would in itself be
expected to provide a significant deterrent against human encroachment.
Potential Impacts
The loss of integrity of the waste disposal system as a result of an engineered system
failure, natural phenomena, or human encroachment might give rise to environmental conse-
quences by introducing radioactive waste into the biosphere, which would result in radiologi-
cal health effects. Similarly, ecosystem effects and nonradiological health effects are con-
ceivable.
Radiological Health Effects. It is difficult to predict the nature of future events that
would cause a breach of the barriers isolating the nuclear waste from the biosphere. Hence,
it is assumed that the system would perform as designed for a prespecified period of thou-
sands of years (Bechtel 1979a). After the period in which the isolation scheme performs as
engineered, the barriers would be assumed to be susceptible to breach by:
* Normal degradation, due to expected, naturally evolving events, such as breach by an
aquifer with the eventual leaching and migration of the waste
* Abnormal penetration, due to unexpected events, such as drilling or mining of the
waste site by man.
The actual scenarios are described in detail in Bechtel (1979a). The radiological impact is
expressed in terms of dose per year or dose per event in the case of the abnormal occurrence.
The impacts are given in Table 6.1.7.
Ecosystem Effects. An evaluation of the effects on the ecosystem in the long term re-
quires data that are presently unavailable. However, it is not expected that the impact on
the ecosystem would be any greater than that for a mined geologic repository, and maybe less,
since the radionuclides would be expected to take longer to reach the biosphere.