Piping and Valves - STD-1128-98master0318

DOE-STD-1128-98

Guide of Good Practices for Occupational Radiological Protection in Plutonium Facilities

systems. Other materials may be used if engineering analyses demonstrate that

criteria are met for strength, smoothness, porosity, and corrosion resistance for the

liquids to be handled.

Piping systems used for conveying radioactive and corrosive materials should be of

welded construction whenever practicable. Flanges should be used only when

absolutely necessary for servicing.

Positive measures should be taken to prevent any radioactive material in the facility

from entering a utility service. This may be achieved by using backflow-

prevention devices and by prohibiting direct cross-connections 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.

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