Materials - std60030149

DOE-STD-6003-96

c. Materials

Materials of construction should be resistant to the chemical, high-temperature, low-

temperature, and other anticipated hazards. The specific hazards to be addressed are relative

to the equipment's expected location within the fusion facility. Major concerns are the activation

of materials by the intense neutron bombardment, the degradation of materials by all forms of

radiation, the contamination of surfaces from the transfer of radiological materials, and the

embrittlement of materials from exposure to hydrogen isotopes.

Activation and degradation issues should be addressed by careful choice of materials.

Materials should be radiation tolerant to the cumulative exposure expected during their service

life with an acceptable margin for safety. Design values that have proven acceptable in practice

are 1 108 rads for replaceable materials and 1 109 rads for inaccessible materials. Structural

materials should be chosen for their nonoxidizing surface characteristics and resistance to neu-

tron activation, to the extent possible. Stainless steels should be used unless other materials are

acceptable. Nonmetallic materials should be chosen for their resistance to neutron activation

and to radiological degradation. The failure mode of the materials should not directly cause fail-

ures of other systems (e.g., elastomers that become liquids upon radiological exposure). Non-

metallic materials that cause degradation of adjoining metallic materials, such as materials that

release chlorine, should not be used.

The contamination issue should be addressed by careful surface selection and prepara-

tion to prevent the entrapment of radioactive materials and facilitate the removal of material.

Metal surface characteristics should be smooth and free of paints or coatings, with the excep-

tion of strippable coatings used for decontamination. High-polish or electropolished surfaces are

preferred, due to their ease of decontamination.

Materials should be resistant to degradation by decontamination processes to be used

prior to maintenance. These methods include cleaning with high-pressure water, cryogenic

materials, and mild acids. Special care must be used to prevent gaps and crevices from entrap-

ping and retaining radiological materials.

General guidelines for the selection of materials include the following:

1. The effects of galvanic or chemical corrosion should be evaluated as part of the

material selection process.

2. Lubricants, sealants, and protective coatings should be compatible with their

intended service and environment.

3. Materials selection, including lubricants, sealants, and electrical insulation for

equipment, should consider the design-life radiation exposure (during normal

operation and, where applicable, off-normal event conditions) to ensure no loss in

function for the design life of the equipment. Materials that will preclude or mini-

mize generation of mixed wastes should also be considered.

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