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

4.53
TABLE 4.4.1. Estimated Radionuclide Releases During Water Basin Storage of Unpackaged
Spent Fuel
Fraction( a ) Released During Fraction(a) Released Each
Fission Products Receiving or Shipping Year During Storage
H 2 x 10- 6 1 x 10-6
Kr 6 x 10 -5 7 x 10 -7
I 1 x 10 -7 9 x 10-9
Cs 7 x 10 - 11 9 x 10 -12
All Others 2 x 10- 12 2 x 10- 13
Actinides Negligible Negligible
Activation Products
C 3 x 10- 6 1 x 10-8
All Others 2 x 10-10 2 x 10-11
(a) Fraction of activity in spent fuel released to atmosphere. See
Tables 4.2.2 and 4.2.4 for the activity in spent fuel.
The radionuclide emissions from a facility storing packaged fuel will be markedly lower
than those from a facility storing unpackaged fuel. The radionuclide emissions are assumed
to be negligible since the containment of the fuel elements in high-integrity packages will
reduce the emissions by at least several orders of magnitude below the already low releases
resulting from storage of unpackaged fuel.
4.4.1.3 Air-Cooled Vault Storage of Packaged Spent Fuel
Another alternative for extended storage of packaged fuel involves packaging in carbon
steel canisters and storing in heavily shielded, air-cooled concrete vaults. The conceptual
facility (see DOE/ET-0028, Section 5.7.6), is an adaptation of a storage concept for solidified
high-level waste (ARHCO 1976). In this concept natural-draft air circulation is used
to remove decay heat so that no mechanical equipment is required for heat removal. The
spent fuel canisters are placed vertically within steel sleeves in the vault; these sleeves
increase the natural air flow velocity around the canisters and provide additional heat
transfer area for the air coolant. Air enters a bottom plenum through side inlets in the
structure, passes upward through annuli formed by the storage units and sleeves, and is dis-
charged through an exhaust port to the atmosphere. Air flow is induced by the decay heat of
the spent fuel and the design of the vault. This concept has not been used for fuel stor-
age, but is based on established engineering practice and principles.
Double containment of the radionuclides maintains radionuclide emissions at negligible
levels. Double containment is provided by single encapsulation of unfailed fuel assemblies
(cladding is one barrier and the canister is the second) and by double encapsulation of
failed fuel assemblies. A more conservative approach would be to doubly encapsulate all of
the assemblies.