Structural Design - std60030114

DOE-STD-6003-96

gas or reduced oxygen atmosphere). Subsequent levels of confinement will provide monitoring

capabilities commensurate with the hazard anticipated and the operating requirements of the

barrier.

d. Structural Design

See Section 6.1.3.4 for general guidance. Tritium systems that are safety-class should

have design, fabrication, inspection, and testing in accordance with a recognized safety-related

code. The specific codes and criteria selected should be commensurate with the level of safety

required and should have a documented technical justification.

Tritium systems that are not safety-class should have design, fabrication, inspection, and

testing in accordance with a recognized national consensus code.

e. Tritium Embrittlement

The structural design analysis should use material properties that account for tritium and

helium embrittlement at the projected end-of-life. Tritium embrittlement adds a physical mecha-

nism to the generally understood hydrogen embrittlement. Tritium permeates the metal struc-

ture, like other hydrogen isotopes, but tritium decays to produce interstitial helium-3. The helium

damage is additive to the damage caused by the tritium.

Conversion of Elemental Tritium to Tritium Oxide

The design should include engineered features as necessary to minimize the potential for

tritium contact with ignition sources, water, moisture, hydrocarbons, and other oxidizing sources.

Because oxidized tritium presents a significantly higher biological hazard than elemental tritium,

the design must reduce to a practical minimum the unintended conversion of tritium to any oxi-

dized form. It is recognized that some tritium cleanup systems convert elemental tritium to an

oxide form with deliberate intent to facilitate removal from flowing gas streams.

g. Exchange with Hydrogen, Hydrogenated Compounds, and Hazardous Wastes

Designers should avoid use of water, moisture, mercury, hydrocarbons (oils), plastics,

asbestos or elastomeric gaskets, and other hydrogenated compounds that could contact tritium.

Gaskets and o-rings in contact with tritium should not use elastomers, plastics, or asbestos; tri-

tium will degrade them, cause premature failure, and may create a source of mixed waste. Ultra-

high molecular weight polyethylene (UHMWPE) and certain polyimides such as VESPEL are

exceptions to this rule. Valves with UHMWPE stem tips will remain leak tight longer than valves

with metal (e.g., stellite) tips.

h. Hydrogen Fires and Detonations

Hydrogen fire or detonation requires the following concurrent conditions: hydrogen iso-

topes in sufficient concentration, oxygen in sufficient concentration, and high temperature or

ignition source.