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

6.34
be: (1) the pipe and valve manifold enclosure, (2) the condensing plant, and (3) gas pro-
cessing equipment. Pipe and valve manifolding would be located in an enclosure near the top
of the cavity operating shaft. The cooling water injected into the cavity and the steam from
the cavity would be routed through this enclosure. There would be an operating and
instrumentation gallery adjacent to the enclosure (Bechtel 1979a). (The HLLW would be
charged through a separate underground pipe, mentioned above, that would not go through the
confinement building or the pipe and valve manifold enclosure.)
The condensing plant would cool and condense the steam coming out of the cavity and re-
cycle it as cooling water during the waste charging phase. The potentially radioactive prim-
ary cooling loop and the nonradioactive, closed-circuit intermediate cooling loop, along with
the associated pumps and heat exchangers, would be shop fabricated in modules and designed
for rapid remote maintenance. Since the rock would start to melt in a matter of days without
cooling, all heat exchanger and pump systems would be designed and constructed with full re-
dundant capacity to ensure constant cooling.
Most of the gaseous elements in spent fuel would be removed during reprocessing at the
fuel reprocessing facility. However, some fission product iodine in the liquid wastes could
become volatile during the waste charging phase and would be carried out with the steam.
This would be trapped by the gas processing equipment and returned with the cooling water to
the waste charge or packaged for disposal in a mined geologic repository (Bechtel 1979a).
Auxiliary facilities would support the systems and equipment located inside the con-
finement building. These would include the water treatment plant, cooling tower, and
radwaste treatment (Bechtel 1979a).
Sealing Systems. There would be two principal shaft sealing operations:
1. Sealing of the spare shaft after construction and before waste charging begins
2. Sealing of the charging shaft after completion of waste filling but before rock
melting begins.
The NRC's Information Base for Waste Repository Design (NRC 1979) provides recommenda-
tions for sealing conventional boreholes and shafts. Though this information base may not be
particularly applicable to the rock melt concept, it states that removal of the steel casing
is essential for long-term performance of the seal. The seal must be bonded directly to the
geological strata for maximum strength. Expansive concretes make the best seals under cur-
rent technology and do so at an acceptable cost. However, it is not certain that these
seals, whether cement, chemical, or other material, will successfully resist deterio-
ration over a period of 1,000 years on the basis of current penetration sealing technology.
Seal failure must be assumed even for seals placed under carefully controlled conditions us-
ing state-of-the-art technology and materials. Further development of sealing technology
would, therefore, be required (DOE 1979).
Postemplacement sealing of the pipes within the shaft, the shaft itself, and the pipes
and valve gallery in the confinement building would be a more complex problem. This is be-