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

IDSIE
BOULDER BATHOLITH I
BATOLIVADA TH .,
RAITS RAAINEGRANIES
I -
B.18
PRECAMBRIAN NORTHERN
SHIELD GRANITES IMARITIMEI
i - APPALACHIANS
-I - APPALACHIANS
GRANITIC
CRYSTALLINE ROCKS
FIGURE B.6.2. Granitic Rock in the United States
(adapted from Office of Waste Isolation
1978a)
B.6.3 Shale Properties
NAPPALACHIANS
Shale is the product of the lithification or compaction and cementation of mud. Mud
is predominantly composed of clay size particles (1/256 mm dia) and/or silt size particles
(1/256)to 1/16 mm dia). The predominant constituents are clay minerals (hydrous aluminum
si.l.iicaes)),, and substantial amounts of mica, quartz, pyrite, and calcite (Table B.6.1)
((Verftcrgem et aili. 1970, Holmes 1978, Office of Waste Isolation 1978a). Mineral grains may
either be- poonly compacted in a soil-like manner or cemented like rock. Shales are in gen-
eral stratif"iedior laminated, and fissile, although some may show little layering and break
into small angullar- blocks, as with mudstones. Shales are often interbedded with other sedi-
ments such as carbonates and sands. Shale units potentially applicable as disposal media
are situated in sedimentary basins throughout many of the contiguous 48 states, as illus-
trated in Figure- P.6.3 (Office of Waste Isolation 1978a).
Shales are rel'atively weak, partly because of the soft mineral components and weak
cementation between grains. The general texture is fine-grained, and shale tends to split
into flat, shell-like fragments in parallel bedding. The fine-grained clay minerals account
for a very high natural moisture content and porosity. Because of fine pore size, inter-
granular permeability, is low. Many shales have the ability to accommodate large deforma-
tions with a potential for plastic flow.
Clay minerals are known to have a high ion-exchange potential. Wetting and drying of
shale will weaken the rock and may cause it to crumble. Shale may oxidize (as well as dry)
when exposed to air, affecting both strength and volume characteristics. More data are