Piping and Valves - doe-std-1128-98

DOE-STD-1128-98

design should provide sufficient space and versatility to accommodate equipment

for programmatic changes and process modifications.

The initial line of defense to protect workers in a process area is the primary

confinement system, which includes enclosures, glove boxes, conveyor lines, the

ventilation system, and process piping. The primary confinement system should be

designed to minimize the impact of accidents and abnormal operations on people,

facilities, and programs. The type of confinement enclosure used (e.g., hood, glove

box, remote operation cell) depends on the amount and dispersibility of unsealed

plutonium that will be handled and on the process involved. Generally, if the

quantity of unsealed plutonium exceeds 100 mg, the use of a glove box should be

considered. However, the applicability of this guideline will vary based on the

individual merits of each case.

C.4.3.1

Piping and Valves

Piping and valves for radioactive liquids should not be field-run (i.e.,

pipe and valve locations should be located as specified on approved

drawings and not at the discretion of the installer).

Notches, cracks, crevices, and/or rough surfaces that might retain

radioactive materials should be avoided in the design of radioactive

piping systems.

The piping system that collects contaminated liquids should be designed

so that effluent from leaks in the system can be collected without

releasing the liquids into personnel-access areas or to the environment.

When component or system redundancy is required, sufficient separation

of equipment should be employed so that redundant systems (or

equipment) cannot both be made nonfunctional by a single accident.

Stainless steel should be used in all radioactive waste and process system

piping and equipment to ensure that smooth, nonporous, corrosion-

resistant materials are in contact with contaminated liquids. For some

applications, polyvinylidene fluoride (PVDF) piping may be preferred

for inside of confinement enclosures because of its ease of fabrication,

smoothness, nonporosity, and corrosion resistance. However, it

undergoes severe degradation after about 7 x 107 rad of exposure. In

general, organic materials should not be used in process-piping 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

back flow prevention devices and by prohibiting direct cross-connections

C-12