Structural Design Codes

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