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

5.66
5.4.6.6 Environmental Effects Related to Postulated Radiological Accidents
Several accidents that could result in the release of radionuclides were analyzed for
the spent fuel repositories. The accidents were chosen on the basis of their probability
of occurence and radiological consequences. Of accidents which might occur during the
operation phase, the drop of a spent fuel canister down the repository mine shaft was most
serious and its effects are presented here. Severe accidents after repository closure are
treated in Section 5.5. Scenarios are provided in DOE/ET-0028.
For the accident involving a canister dropped down a repository mine shaft, radionu-
clides are assumed to be released to the mine atmosphere from the failed canister over a
period of 1 hr. An elevator load is assumed to include four spent fuel assemblies contain-
ing 2 MTHM of spent fuel that are assumed to be ten years out of the reactor. The radioac-
tive materials that would be released to the environment from such an accident are presented
in Table 5.4.22. The releases were determined using the assumption that material released
in the mine shaft passes through a roughing filter and two HEPA filters (total Decontamina-
tion Factor (DF) for particulates of 107) prior to release to the environment through a
110-m stack. Frequency of occurrence of the accident is postulated to be 1 x 10 -5 per year.
Based on these releases, the 70-yr whole-body dose commitment to the maximum individ-
ual(a) was calculated to be 3.5 x 10 - 5 rem. The 70-yr whole-body doses to the world-wide
population would be 8.7 man-rem, compared with 4.5 x 1010 man-rem from naturally occurring
sources.
Accidents were also postulated for the geologic repository for reprocessing wastes
that might lead to release of radionuclides to the environs and are listed in Table 5.4.23.
Scenarios are provided in Section 7.3.1.9 of DOE/ET-0028 and analyses of the accidents are
presented in DOE/ET-0029. Non-design-basis accidents are discussed in Section 5.5.
Of the minor accidents, the contact-handled transuranic (CH-TRU) waste drum rupture
accident (handling error) was considered most representative of the.minor accidents. In
this minor accident, a forklift operator error is assumed to result in the breach of one
drum of CH-TRU waste. The accident can occur in the surface facility or in the CH-TRU waste
mine shaft and has an estimated frequency of 0.15/yr. For the 0.63 MTHM equivalent con-
tained in a single drum, a release fraction of 2.5 x 10 -5 over a release time of 30 minutes
was used.
Radioactive materials that would be released to the outside environment from this acci-
dent are presented in Table 5.4.24. The releases are assumed to be the same whether the
accident occurs in the surface facility or the CH-TRU waste mine, since all releases would
be released from a mine exhaust stack approximately 100 m high.
(a) The maximum individual is defined as a permanent resident at a location 1600 m southeast
of the stack with the time-integrated atmospheric dispersion factor (E/Q) of
1.3 x 10 -5 sec/m 3 .