Computer Code Verification

DOE-HDBK-6004-99

safety analysis (guidance on leak testing is provided in 10CFR50(J). All vacuum vessels that

provide a confinement barrier should be leak checked before initial operations and periodically

thereafter against the leakage criteria in the facility safety analysis. The vacuum vessel chamber

should be pneumatically tested in accordance with ASME 93 or comparable safety-related code.

A double-walled vacuum vessel should be hydrostatically tested in accordance with ASME 93

or comparable safety-related code.

2. Valves - System isolation valves should be hydrostatically tested in accordance with the ASME

93 or a comparable safety-related code.

Computer Code Verification

Computer codes used for design analysis of the vacuum vessel for normal operating and design basis

accident conditions should have validation and/or verification as described in DOE Standard 6003-96.

This validation and verification should support the use of the code in each intended application.

Materials

Material properties used in the structural analysis of safety-class structures, systems, and components

must be appropriate for the operating environment and compensated for the degradation of the

material with time due to radiation, fatigue, corrosion, or any other harsh treatment.

1. Radiation - Materials selected should be qualified for the anticipated lifetime in the radiation

environment. With irradiation, yield strength usually increases as ductility decreases.

Conservative end-of-life properties should be used in the structural design analysis.

2. Thermal - Material properties used in analysis should always be those appropriate at the given

temperature. If no published property data for a particular temperature exists, then materials

should be tested for properties at the operating temperature. For those items to be designed in

accordance with the ASME Boiler and Pressure Vessel Code, temperature limits are imposed

within the Code. If the item will be subjected to temperatures higher or lower than the limit,

material properties, such as allowable stress and creep, used in the analysis should be justified by

testing the material at the anticipated temperature.

3. Swelling - The energetic neutron flux on the first wall, diverter and other plasma facing

components results in displacement cascades and helium-producing nuclear reactions. During

long-term irradiations vacancies coalesce to form helium-filled voids within the material.

Dimensional changes are most severe at about half the melting point of the material. Allowance

must be made for irradiation-induced swelling in the design of any components exposed to the

high-energy neutron flux.

4. Hydrogen Embrittlement - Hydrogen reacts to some degree with almost all metals. When a metal

comes in contact with hydrogen, its surface adsorbs the gas. Surface or physical adsorption is

followed by activated adsorption, a preliminary stage of the diffusion of hydrogen into metals.

With continued exposure, materials can become embrittled. The material properties based on

end-of-life hydrogen embrittlement should be used in the structural design analysis. The actual