inside the facility. The most successful backflow-prevention device is the
deliberate separation of lines.
Every pipe that enters or exits a process cell or contaminated area from
or to occupied areas should be equipped with block valves.
Process-piping systems carrying radioactive liquids should be designed
to eliminate traps wherever possible and to permit flushing and draining
except for those with loop seals. Floor drains should have the capability
to be sealed.
Reduction in the size of pipelines in contaminated process-piping
systems should be made with eccentric reducers installed flat-side down
to avoid the formation of traps. Eccentric reducers are necessary only for
horizontal pipe runs.
Changes in the direction of process piping should be made with long-
radius elbows or bends. Long-radius bends should be used, where
practicable, except in lines that transport solids, where blinded tees or
laterals have been proven to prevent erosion. Blinded tees will encourage
solids buildup. The number of bends should be minimized and pipe
diameter should be increased.
If gaskets are required in process piping or associated hardware, the
selected gasket material should not deform or degrade and leak when in
service. Teflon should be avoided for most applications but, if needed, its
use will require implementation of a most rigorous inspection routine to
ensure recognition of degradation and replacement prior to failure.
Except for shielding walls, pipe sleeves should generally be provided
when piping passes through masonry or concrete walls, floors, and roofs.
The sleeves should be sloped to drain toward the controlled area. The
space between the pipe and the sleeve should be packed and sealed. If the
sleeve is to be sealed, then additional provisions should be made for
draining the annulus.
If underground piping for transporting radioactive or hazardous materials
is required, it should be installed inside another pipe or tunnel that
provides a second barrier to the soil. Provisions to detect a failure in the
primary piping (leak detection) should be provided. An effective solution
may be to install a double-walled pipe with an annular space that can be
sampled at intervals not exceeding 300 feet. The underground piping
should also have cathodic protection.
All valves that are not functionally required to be in contact with
contaminated liquids should be located in nonradiation areas (e.g., steam,
air, water) in accordance with IAEA Safety Series No. 30 (IAEA, 1981).
Process valves should not be located at low points in the piping except in
cases where it is necessary in order to properly drain the piping when