Design Objectives - STD-1128-98master0230

DOE-STD-1128-98

Guide of Good Practices for Occupational Radiological Protection in Plutonium Facilities

Because confinement systems are subject to component failures and other accidents,

differential air pressures are normally maintained so that a breach of containment will not

affect occupied areas or the environment. Glove-box lines are at the lowest pressure,

plutonium laboratories at a higher pressure, and other occupied areas at the highest pressure

but still negative with respect to the outside.

Because plutonium air-cleaning systems are usually expensive to service (requiring workers

to be dressed in multiple layers of protective clothing and respiratory protection), and

plutonium waste is expensive to dispose of, measures are taken to protect the life of

plutonium air-cleaning systems. Extraneous particulates are eliminated by HEPA filtration

of incoming air. (These HEPA filters may be disposed of as sanitary waste.) Roughing pre-

filters are used to capture the bulk of particulates and prolong the life of HEPA filters.

Care must be taken in designing HEPA filter installations for plutonium facilities so that

provisions are made to safely change the filters while maintaining contamination control.

Such measures normally include redundant banks of filters (in parallel) that can be valved

out for filter change, location of HEPA filter banks in enclosed rooms that are themselves

HEPA-filtered, and appropriate provisions for filter bag-out.

New filters must be tested after they are installed to ensure proper gasketing, etc. Once in

place, they must be periodically retested to ensure that HEPA efficiency is maintained. For

this reason, HEPA filter installations must have ports for the introduction of a challenge

aerosol upstream of the filter and collection of a representative sample in a region of laminar

flow downstream of the filter. The HEPA filters in plutonium use sometimes fail from

mechanical fatigue and vibration rather than plugging or being subject to some other

mechanical failure. The proper design of HEPA filtration systems and proper sampling

provisions are discussed in DOE Order 6430.1A, General Design Criteria (DOE, 1989b);

ANSI N510-1989, Testing of Nuclear Air-Cleaning Systems (ANSI, 1989d); ANSI/UL

586-1990, High-Efficiency Particulate Air Filter Units (ANSI, 1990); ANSI/ASME N509-

1989, Nuclear Power Plant Air Cleaning Units and Components (ANSI, 1989b); DOE

Implementation Guide. Workplace Air Monitoring (DOE, 1994g); and ANSI N13.1-1969,

Guide to Sampling Airborne Radioactive Materials in Nuclear Facilities (ANSI, 1969b).

In addition to the above features of the air-handling system, there may be process-selection

features that will minimize the generation of airborne plutonium. If at all possible,

plutonium compounds should be handled in sealed containers or, in the case of a metallic

solid, the material encapsulated. Wet mechanical processes, such as cutting and grinding,

usually generate fewer particulates than dry ones, so they are often preferred. However, it is

also important to minimize the use of chemicals that will attack the air-cleaning system or

contaminate the filters with hazardous chemicals, making them mixed waste. Even moisture

will shorten the life of HEPA filters, so wet processes should be enclosed to the extent

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