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

oundary conditions at the emplacement hole surface are provided in a three-dimensional
K.6
Cartesian near-field model with asymmetric spacings between canisters. The heat-generating
waste and waste canister are explicitly described as well as the properties of the rock in
the pillars and above and below the waste storage room. The storage room was not modeled
since it has little impact on canister temperatures. The storage room including radiative
and convective heat transfer effects has been included in other calculations, however. The
boundary conditions above and below the storage room and canister are provided in a far-
field model. Temperatures in this model are calculated in cylindrical symmetry and
stratigraphy of the host formation can be explicitly modeled.
The thermal load limits and the controlling factors associated with each limit gener-
ated by these analyses for 10-year-old spent fuel and HLW are presented in Table K.1.2. The
far-field average repository loading limits are based on the far-field studies and the esti-
mated maximum uplift of the formation caused by heat from the stored waste. Far-field aver-
age repository thermal loading limits apply to the thermal density of wastes averaged over
each waste type's overall emplacement area, including corridors and ventilation drifts and
excluding the areas for shafts or emplacement areas for other waste types. In linear ther-
momechanical expansion studies for salt, a surface uplift of 1.2 to 1.5 m was obtained for
average far-field loadings shown in Table K.1.2. This maximum uplift is felt to be accep-
table for a repository at 600 m over the time frame involved (Russell 1977). Similar calcu-
lations for granite and basalt for loadings of 190 kW/acre, and shale for 120 kW/acre, give
less than 0.4 m of surface uplift. Although Table K.1.2 indicates that thermal loading
limits for both the far-field and near-field for spent fuel and HLW in granite, shale, and
basalt, and for HLW in salt are equivalent, the far-field average repository loading will
always be less because of the passive regions of the repository such as corridors and waste
handling areas.
The near-field local areal loading limits are based on room and pillar stability con-
siderations. Near-field local thermal loading limits are applied to the thermal density of
wastes in an individual waste type's emplacement room area including the area of one-half
the rock pillar on each side. Areas for corridors, shafts, and other waste type emplacement
areas, are excluded. Linear thermomechanical analyses based upon the predicted near-field
temperature distributions indicate that readily retrievable operations could continue in
the storage rooms for at least 5 years with the loadings in Table K.1.2 (Dames and Moore
1978).
Although salt can accept 150 kW/acre based on room and pillar stability considerations,
this density cannot be achieved in the case of spent fuel because of the more limiting far-
field criteria. Reduced loadings are necessary here because of the long-term heat contribu-
tions from the plutonium as shown in Table K.1.3. The additional long-term heat contribu-
tion of the plutonium does not affect room stability but does increase surface uplift. In
order to meet the far-field limit of 60 kW/acre, the maximum near-field density that can be
achieved is 75 kW/acre for spent fuel. All other wastes may be emplaced at the 150 kW/acre
near-field and far-field criteria for nonplutonium wastes in salt.