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

5.74
Fuel Reprocessing Waste
Spent Fuel HLW RH & CH-TRU
Salt 51,000 MTHM(a) 62,000 MTHM 100,000 MTHM
Granite 122,000 69,000 108,000
Shale 64,000 30,000 56,000
Basalt 122,000 56,000 92,000
If the amount of disposed waste, rather than the size of the repository, were held constant,
the radiological consequences would be the same for each geologic medium. In other words,
once the radionuclides are outside the repository proper, their movement away from the
repository is governed by the same set of assumptions regardless of repository media. (This
limitation of the analysis would be improved upon in site-specific analyses when site spe-
cific data or sorptive properties of adjacent rock become available.)
In the case of faulting and flooding with stream transport the assumption was made that
the same amount of waste was removed by water regardless of repository medium. Repository
medium affected consequences only in salt repositories; the presence of salt along with the
wastes would likely preclude use of the emergent stream as a source of drinking water or
food. Thus, except for the case of salt entering the biosphere with the waste radionuc-
lides, no analysis was made of the waste repository medium's influence in the consequences
of the postulated long-term events.
In the case of human intrusion by drilling, the same amount of waste was assumed to be
brought to the surface regardless of repository media.
5.5.1 Repository Breach by Meteorite
Breach of a repository would be possible by a meteorite estimated to be about 25 m in
diameter striking a point on the surface above the center of the repository at a speed of
about 20 km/sec on impact. If the meteorite's density is 8 g/cm 3 (which is representative
of iron or nickel-iron meteorites), the mass of the meteorite at contact would be about 6.5
x 104 MT and would have an energy equivalent to about 3 megatons of TNT. This meteorite
would produce a crater roughly 2 km in diameter at the surface and 600 m deep at its deepest
point. No clear evidence is available to suggest that meteorites of this size have created
craters this deep over the age of the earth. On the other hand, the presence of astroblemes
suggests that the earth has been hit by very large extraterrestrial bodies (Claiborne and
Gera, 1978).
Temperatures at the impact point of the meteorite strike would reach millions of
degrees, and most of the meteorite plus some of the surrounding rock would be vaporized.
Some of the rock material would be pulverized and ejected into the air as the crater formed.
Most of the ejected material would fall back into the crater and its immediate vicinity.
(a) Metric tons of heavy metal in the case of spent fuel or spent fuel equivalent in the
case of reprocessing wastes.