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DOE-HDBK-6004-99
associated individual components are safety-class and the design should consider them as the primary
confinement barrier for all operational and design basis modes.
Secondary confinement includes the 1) barriers that enclose the primary confinement and 2) systems
that ventilate the secondary confinement volumes. If the safety analysis deems a portion or all of
secondary confinement to be a safety-class system, the associated individual barrier components are
safety-class and the design should consider them as confinement barriers for all operational and design
basis modes. Examples of secondary confinement systems are glove boxes, sealed enclosures, bell
jars, double jacketed vessels/duct work/piping, and stripper/scrubber systems. Ventilation systems
for secondary and higher order confinement volumes will operate at a negative pressure relative to
the ventilation systems of zones occupied by personnel. The negative pressure will assure that any
air flow between zones will flow from personnel zones and into the zones that could be confining a
tritium release.
Structural Design Codes
The design, fabrication, testing and inspection of safety-class tritium structures, systems or
components should be in accord with the ASME Boiler and Pressure Vessel Code (ASME 93a), or
to a comparable safety-related code.
Either ASME Code Section III, Class 1 or 2 or the comparable elements of ASME Code Section
VIII, Division 2 may apply for pressure vessels. For tritium systems, ASME Code Section III is
acceptable. ASME Code Section VIII is acceptable if the design uses additional standards in areas
such as attached valves, pumps, piping and supports, enhanced quality assurance and tritium/helium
embrittlement effects which are comparable to relevant parts of ASME Code Section III.
In general, the designer should prepare a detailed comparison between ASME Code Section III and
the comparable code, for safety-class systems, and demonstrate comparability. The designer should
prepare this comparison early in the design phase and the safety regulatory or licensing authority
should endorse the comparability to ensure acceptability for construction. Finally, this document does
not address the actual stamping of a vessel or component complying with Section III or VIII; this is
a decision among the owner, fabricator and the cognizant regulatory agency.
Hydrogen Fire and Detonation
Hydrogen fire and detonation are potential hazards which the safety analysis may declare design basis
accidents (typical frequency > 10-6/year). If tritium primary confinement is a safety-class system,
it must retain a required integrity during and after a fire or detonation event, although the non-safety-
related functions of the confinement can be compromised. If it is not a safety class, the tritium
primary confinement may fail in a fire or detonation event, but the failure should not degrade the
function of an adjacent safety-class system, structure or component.
Hydrogen Fires
The hydrogen isotopes tritium, deuterium and protium leak easily and can form a highly flammable
mixture with air. Hydrogen and air mixtures can ignite and sustain a flame over a very wide range
of composition, from 4% to 74% by volume of hydrogen, at room temperature and pressure (Hord
78). A minimum limit of 9% is needed to sustain a coherent flame. At room temperature and
44


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