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

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a few years. For purposes of this accident analysis the well(s) could operate for 50 years
before being abandoned because of failure caused by cave-in and crushing and plugging of
piping with debris.
This accidental repository intrusion, as in the case of the drilling accident, is based
on the assumption that repository markers are either no longer evident, are misunderstood or
ignored. Salt deposits are relatively plentiful and drilling to 600 m for salt seems
highly unrealistic. No probabilities could be assigned to this event; it is presented only
as a hypothetical "what if" accident.
Ordinarily, once the brines are brought to the surface they are analyzed to determine
the kinds and amounts of impurities such as calcium sulfate, calcium-magnesium carbonate,
sulfides, etc., which would govern further processing to purify the salt. If radioactive
waste is placed in repositories in salt formations, salt used for human consumption could
be checked by radioanalysis as well (an institutionally administered precaution). Calcula-
tions suggest that radioactivity would be determinable with off-the-shelf gamma-ray spec-
trometer apparatus on samples of a few hundred grams at concentrations of waste in salt
existing after a few days of mining operation and with certainty by one month of mining
operation.
Assumptions of the scenario are that, although the salt stratum of the reference site
is about 80 m thick, the salt removed is principally that from backfill, ceiling, pillars
and floor where radioactive waste has been placed. In mining the repository.about 33 mil-
lion tons of salt would have been removed for waste placement. This represents about one-
fourth of the total salt volume in the mined area (in the scenario, the repository has been
backfilled completely with salt; actually backfill of about 60% is presently planned). The
total salt postulated to be solution mined over 50 years is then about 130 million tons.(a)
This represents about 10% of the total salt contained in the salt stratum bounded by the
repository area. If an equal amount of salt is mined in each of 50 years, the annual pro-
duction would be about 2.6 million tons. In 1957 about 24 million tons of salt were pro-
duced in the United States (Kaufmann 1960). Such a solution mining operation for salt would
exceed the size of those presently in operation in the United States; a very large operation
in the United States produces about 0.4 million tons annually and in Europe a very large
operation may produce on the order of 1 million tons of salt annually.
Given that 100 parts of water (at 20 to 100 C) by weight can dissolve 36 to 39 parts of
salt, then over a 50-yr period a stream flow of 210 /sec is required to dissolve that much
(a) Although it is believed that radioanalysis of salt would result in termination of the
operation soon after start-up, the scenario is developed based on removal of the repository
salt over a 50-yr period. Amounts of wastes and salt brought to the surface
over shorter periods of time are pro-rated based on water contact with all wastes by
the end of 50 years. Consequences are based on the assumption that the presence of
radioactivity goes undetected for one year.