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

6.42
Radiological Impacts. During presealing operations, waste in solution or slurry form
would be introduced directly into the repository cavity. Various operations in this charging
phase could lead to release of radioactive material into the environment.
Under normal operating conditions, the casing in the emplacement well should prevent con-
tact of radioactive waste with any aquifers that would overlie the disposal cavity. During
waste charging, however, it would be possible that some radioactivity could migrate out of
the cavity and into the surrounding rock. This possibility would be reduced if the cavity
were maintained approximately at atmospheric pressure. Under these conditions, the tendency
of water under hydrostatic pressure to flow into the cavity would minimize the importance of
this transport mechanism. Nevertheless, it would be possible for radioactive material to
reach man through such migration into the surrounding rock and onto the biosphere.
Operational impacts would vary somewhat, depending on which version of the rock melting
concept is considered. If liquid HLW were emplaced directly into a cavity from the proces-
sing facility, there would be no impacts due to transportation of the waste. If solid waste
were slurried into the repository, impacts of waste transportation from the reprocessing
plant to the repository would have to be considered. However, such transportation would have
no different environmental effects than would the shipping of such wastes to any other type
of repository.
Treatment of HLLW prior to emplacement might be required to enhance the compatibility of
the liquid with the rock in which the cavity would be located. This additional treatment
step would increase the probability of occupational and population exposures to radiation.
Handling and treatment of solidified HLW would also increase the probability of radiation ex-
posure; risk analysis would take into account the details of the required handling and treat-
ment procedures.
A summary of potential radiological health impacts was prepared for the rock melting con-
cept (Bechtel 1979a). This study projected the short-term occupational impacts for a single
rock melting cavity, which are presented in Table 6.1.8. For a 5,000 MTHM/yr throughput, it
is estimated that three rock melting cavities would be required and that the impacts would be
linear (Bechtel 1979a). Occupational impacts prior to the waste reaching the repository,
nonoccupational impacts, and impacts from abnormal conditions were also postulated in this
study. For this analysis, the consequence of impacts under abnormal conditions was found to
be comparable to, or slightly less than, those of the other options. This study, however, did
not include any probability analysis and consequently total radiological impacts under
abnormal conditions have not been quantitatively determined.
Nonradiological Impacts. The underground portion of rock melt repositories would proba-
bly be constructed using conventional mining and drilling techniques. Health impacts would
be those typical of any analogous construction project, and would be somewhat dependent on
the method chosen (whether the cavity were created by mining, underreaming, explosive spring-
ing, etc.).