Residual Radionuclides in Air and Water

DOE-STD-1136-2004

Guide of Good Practices for Occupational Radiation Protection in Uranium Facilities

10.1.2.5 Residual Radionuclides in Air and Water

Residual concentrations of radionuclides in air shall not cause members of the public to receive an

effective dose equivalent greater than 10 mrem (0.1 mSv) in 1 year (DOE Order 5400.5, Ch.2). In 40 CFR

141, National Interim Primary Drinking Water Regulations (EPA 1992c), EPA provides a limit of 4

mrem/y annual dose equivalent to the whole body or any internal organ of any member of the public from

manmade radionuclides in drinking water.

NRC is updating their decommissioning regulations and criteria. The new NRC methodology is

presented in NUREG/CR-5512 (NRC 1992c) and is consistent with the recommendations in ICRP

Publications 26 and 30. NRC will establish a three-layered hierarchy for developing decommissioning

criteria to be used to evaluate the release of property after D&D. The first and second layers use

conservative models and parameters, and the third layer uses site-specific models and data to provide a

more accurate approximation of actual conditions. Four criteria will be calculated upon which to make

D&D decisions: 1) a surface contamination level for buildings and building materials (in dpm/100 cm 2),

2) volume contamination criteria for volume sources in buildings (in pCi/g), 3) soil contamination criteria

(in pCi/g), and 4) a total site inventory (in Ci).

These criteria require calculation of dose to members of the general population. The exposure

scenarios will have to include all exposure pathways that are credible under the proposed disposition. If

the site is part of a closely guarded government reservation, certain pathways may be eliminated, such as

the use of well water directly from the site and ingestion of significant quantities of fruits and vegetables

grown on the site. However, if the site will be released for unrestricted use, such scenarios should be

considered. The computer codes used for calculation of dose to the public from decommissioned facilities

will include the currently accepted exposure models and site-specific or maximum credible parameters for

exposure pathways.

10.2 DESIGN FEATURES FOR NEW FACILITIES

Design of the facility should allow easy D&D of equipment and materials. Details on designing

facilities for ease of decommissioning are discussed in the following sections.

10.2.1 Building Materials

In general, the design features that aid in contamination control during operation also facilitate

decommissioning. The inclusion of all the building materials suggested in this section may be cost-

prohibitive, but they should be considered if the budget allows. Maintenance procedures that are used

during operation are also important in controlling the spread of contamination to clean areas and,

therefore, facilitate decommissioning, too.

Less permeable building materials are more easily decontaminated. Any concrete with uncoated

surfaces that comes in contact with uranium solutions or uranium-contaminated air will require surface

removal and disposal as radioactive waste at the end of its life. If there are cracks through which

contaminated solutions have penetrated, the entire structure may need to be disposed of as radioactive

waste.

Metal surfaces may also require decontamination. In general, the more highly polished the surface,

the easier it will be to decontaminate. If feasible, all stainless steel that will come into contact with

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