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

Hole Sleeve
5.10
The function of hole sleeves is to maintain open emplacement holes in the repository
floor for easy package insertion and retrieval. This may be important if the geologic
medium is plastic, e.g., salt or certain shales. In some cases the sleeves could function
simply as barriers that, because of their size and bulk, are more easily constructed in situ
than transported and emplaced with the waste canisters. Examples of sleeve configurations
include cast iron caissons, massive shells of special cements cast in place, or impervious
graphite vessels specially bedded in the surrounding rock.
5.1.2.3 Waste Package Development and Assessment
Although most of the ideas incorporated in the multibarriered waste package just
described are not new, wide-spread acceptance of the waste package concept is a relatively
recent development. A study done in Sweden between 1976 and 1978 did a great deal to pro-
mote acceptance of the concept.
The Swedish Approach to Waste Package Design
In April 1977 the Swedish Parliament passed a law which stipulated that new nuclear
power units could not be put into operation unless the owners were able to show that the
waste problem was solved in a completely safe way. In anticipation of Parliament's action
the Swedish power industry formed the Nuclear Fuel Safety Project (KBS) in December 1976 to
prepare a response to the government (KBS 1978). A primary objective of the KBS project was
to demonstrate how high-level waste or spent fuel can be handled and finally isolated. The
study met this primary objective, and although the results were directed to the specific
needs of one country and assumed a repository located in granite since that type of rock is
widely available in Sweden, the conclusions about the expected performance of the waste
packages can have a wider application.
The KBS decided to place reliance on containment for periods of 1,000 yr and 10,000 yr
for HLW and spent fuel, respectively; thus, design of the waste package received heavy
emphasis. More durable containment for the spent fuel was sought because it produces signi-
ficant amounts of heat for a longer time than does HLW.
In the proposed Swedish waste management scheme for HLW, the fuel is reprocessed 2 to
10 yr after it is taken from the reactor (KBS 1978, pp. 30-34). The HLW is then vitrified
and is placed in cylindrical stainless steel canisters that are stored at the reprocessing
plant for at least 10 yr. After this initial storage period, the canisters are shipped to
an underground air-cooled dry storage facility in Sweden, where they remain for about 30 yr.
Then the packages are prepared for disposal by encapsulation in 6-mm-thick titanium over-
packs. To reduce the intensity of radiation emanating from the packages and hence the
radiolytic decomposition of the ground water eventually expected to surround the package, a
10-cm-thick layer of lead is placed between the steel canister and the titanium overpack.
The packages, now ready for disposal, would be placed in holes approximately 1 m in diameter
and 5 m deep in the floors of tunnels in a granite repository approximately 500 m below the
surface of the ground. Backfill consisting of a mixture of quartz sand and bentonite is