Intermediate-quality Secondary Containment Systems cont'd

DOE-HDBK-1132-99

In each of the examples cited above, substantial amounts of tritium can be at

risk at any given time. Under such circumstances, the rule-of-thumb for the

design of high-quality, secondary containment systems is to assume that there

is no primary containment system, and that the secondary containment system

is the only barrier between the tritium and the outside environment. By default,

therefore, the secondary containment system design requirements become

identical to those used for primary containment systems; accordingly, the

materials and construction issues associated with these types of secondary

systems should also follow the guidance set forth in Section III of the ASME

Boiler and Pressure Vessel Code.

From a materials and construction perspective, there should be virtually no

difference between the requirements for the primary containment and

secondary containment designs. In most cases, the materials of choice will be

a 300-series stainless steel, preferably a low-carbon variety (e.g., 304L or

316L). Welding will be the preferred method of construction wherever

possible. Prior to being placed into service, individual portions of the system

will be certified to a maximum leakage rate of 10 -6 to 10-7 cm3/sec (helium), at a

minimum of 125 percent of the maximum expected pressure.

From an operational perspective, however, the design philosophy should be

that the void volume between the primary containment vessel outer wall and

the secondary containment jacket inner wall in such systems is generally

evacuated during service. Thus, if tritium is released into these secondary

containers, there are no dilution gases present, and any leakage from the

secondary container is in the same form as that contained in the primary

container. Following a release into a high-quality system, the tritium can be

recovered in almost the original purity without dilution by other gases by

pumping it into another primary container. Several days can elapse during the

recovery process without a significant release of tritium to the environment.

Intermediate-quality Secondary Containment Systems . It is not practical nor

possible to enclose all primary tritium systems inside high-quality, nondiluting,

evacuated, secondary containers. Therefore, intermediate-quality, secondary

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