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

6.88
,An important factor in this concept would be the design and shape of the canister, which
should help assure a vertical path from surface to bedrock. In addition to the canister de-
sign and shape, the type of construction materials would be important. Specifications for
these materials would have to include consideration of differences in ice sheet pressure and
the possibility of saline water at the ice/ground interface. A multibarrier approach that
gives consideration to the total waste package and its emplacement environment would be re-
quired. This approach would be equally applicable to the anchored emplacement and surface
storage alternatives.
The anchored emplacement concept, also shown in Figure 6.1.17, would require technology
similar to that required by the meltdown or free flow concept described above, the difference
being that this concept would allow for interim retrieval of the waste (EPA 1979). Here,
cables 200 to 500 m (660 to 1650 ft) long would be attached to the canister before lowering
it into the ice sheet. After emplacement the canister would be anchored at a depth corres-
ponding to cable length by anchor plates on or near the surface. The advantage over the
meltdown concept is that instrument leads attached to the lead cable could be used to monitor
the condition of the canister after emplacement.
Following emplacement, new snow and ice accumulating on the surface would eventually
cover the anchor markers and present difficulties in recovery of the canister. The average
height of snow and ice accumulating in the Antarctic and Greenland is about 5 to 10 cm/yr (2
to 4 in./yr) and 20 cm/yr (8 in./yr), respectively. However, climatic changes might result
in a reversal of this accumulation with ice being removed from the surface by erosion or sub-
limation. If continued for a long period of time such ice surface losses could expose the
wastes. Recovery of canisters 200 to 400 years after emplacement might be possible by using
20-m (66-ft)-high anchor markers. It would take about 30,000 years for the entire system to
reach ice/ground interface at a typical site. During that time, the canisters and anchors
would tend to follow the flow pattern of the ice (Battelle 1974).
The surface storage facility concept would require the use of large storage units con-
structed above the snow surface (EPA 1979). The facilities would be supported by jack-up
pilings or piers resting on load-bearing plates, as shown in Figure 6.1.17. The waste canis-
ters would be placed in cubicles inside the facility and cooled by natural draft air. The
facility would be elevated above the ice surface for as long as possible to reduce snow
drifting and heat dissipation. During this period, the waste canisters would be retrievable.
However, when the limit of the jack-up pilings was reached, the entire facility would act as
a heat source and begin to melt down through the ice sheet. It is estimated that such a
facility could be maintained above the ice for a maximum of 400 years after construction
(Battelle 1974).
Retrievability/Recoverability. Waste disposed of using the meltdown emplacement concept
would be retrievable for a short period, but movement down into the ice and successful