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

5.85
TABLE 5.5.9. 70-Yr(*) Accumulated Whole-Body Dose to Maximum Individual for
Various Leach Rates and Times of Repository Breach by Fracturing and Ground-
Water Intrusion (repository in salt--50,000 MTHM), rem
Spent Fuel Reprocessing Wastes
Breach 1000 years Breach 100,000 Breach 1000 years Breach 100,000
after closure years after clos re, after closure years after clos re,
Years Since Leach Rate (yr- 1 ) Leach Rate (yr- j Leach Rate (yr- 1 _ Leach Rate (yr'_
Disposal 0.1% 0.01% 0.1% 0.01% 0.1% 0.01% 0.1% 0.01%
1.0 x 103 5 x 10- 2 5 x 10 -3 5 x 10- 2 5 x 10 -3
2.0 x 10 3 1 1 x 10-1 4 x 10-1 4 x 1-2
1.0 x 10 4 5 x 10-1 8 x 10 -2 5 x 0 5 x 10-2
3.4 x 10 4 5 x 10- 2 5 x 10-2
1.1 x 105 2 x 10 - 2 4 x 10 -3 3 x 10- 2 3 x 10-2
(*) The computer program for this scenario used 50 rather than 70 years for exposure purposes.
The values tabulated were adjusted upward for an additional 20-year exposure.
each case the host rock was assumed to be surrounded by a common soil-rock medium for which
absorption rates would be the same.
The largest dose tabulated was 1 rem over 70 years if the event should occur. This is
about one-seventh of the dose the individual would have received from naturally occurring
sources and is believed to be of no consequence. The probability of this event occurring
over a 10,000 year period is estimated to be in the neighborhood of 4 x 10 -7 (a )
to 2 x 10-9.
Over a time span of 100,000 years a peak dose occurs that is essentially independent
of leach rate or time of repository breach. The dose is due principally to 226 Ra, decay
product of 238 U (which has an extremely long half-life).(b) At 1.4 million years after dis-
posal the 70-yr dose to the maximum individual amounted to about 70 rem. This long-term radio
logical risk would not be significantly different from that of a natural ore body of similar
content.
Doses to the regional population were not calculated directly for this scenario;
rather, an estimate was made using a ratio of the per capita population whole-body dose and
the whole-body dose to the maximum individual in the previously presented 2.8 m 3 /sec stream
scenario. The ratio obtained was 1/5 and thus the per capita population dose was approxi-
mately one-fifth of the maximum individual dose. A whole-body dose to the regional popula-
tion from ground-water contamination from breach of a 50,000 MTHM repository was estimated
by multiplying the per capita dose by 2 million, the size of the regional population. Tak-
ing the largest maximum individual dose of 1 rem over 70 years to the whole body and using
(a) Probability of faulting over a 10,000 yr period of 4 x 10 -7 was taken from EPA
comment #113 on the draft to this statement. The probability of 2 x 10 -9 over
10,000 years was developed from Claiborne and Gera (1974).
(b) About 10% of 22 6 Ra is a result of decay of 238 Pu produced in the reactor. About
90% of the 226 Ra is from unaltered 2 8 U in the fuel. After long periods of time,
the principal source of potential dose to the public is the uranium from which the
reactor fuel was made.