Systems Performing Safety Functions

DOE-STD-6003-96

b. using an inert gas boundary as discussed above.

6.2 Systems Performing Safety Functions

As stated above, SSCs required for the performance of a public safety function necessary

to meet the evaluation guidelines of DOE-STD-6002-96 should be designated as safety-class.

Section 6.2.1 provides design guidance for systems providing the radioactive and hazardous

materials confinement public safety function. Section 6.2.2 provides design guidance for sys-

tems providing the worker safety function involving control of operating hazards.

6.2.1 Public Safety Function: Confinement Systems

The major public safety function is the confinement of radioactive (e.g., tritium, activated

dust, activation, and corrosion products) and hazardous (e.g., beryllium and vanadium dust)

materials (see Section 6.1.2). The systems that typically provide the first barrier of the confine-

ment boundary (sometimes called primary confinement or containment) are the vacuum vessel

(and associated penetrations) and ex-vessel systems (such as the isotope separation and fuel

storage systems), which provide tritium confinement. Design guidance for these systems is pro-

vided in Section 6.2.1.1, Vacuum Vessel, and Section 6.2.1.2, Tritium Systems, respectively.

The major systems that (typically but not always) provide the second or (if required) the third

barriers of confinement (sometimes called secondary or tertiary confinement) are the cryostat,

ex-vessel gloveboxes/rooms, double-walled piping systems, and/or the fusion building. Design

guidance for these systems is provided in Section 6.2.1.3, Cryostat, and Section 6.2.1.4,

Secondary Confinement Systems. It is emphasized that the number of confinement barriers is

design specific and depends on the anticipated radioactive and hazardous material inventories,

the distance of these sources from the public or workers, the proximity of major energy sources

to these inventories, and the quality and independence of each confinement barrier. For

example, segmentation of radioactive and hazardous material inventories where feasible is a

potential design tool to reduce the number of independent barriers around each individual inven-

tory location. Care must be taken to define the system boundaries carefully and ensure that

adjacent systems are independent and have no common failure modes.

Primary and secondary (or greater) confinement systems are properly viewed as an inte-

grated barrier to provide confidence that net leakage rates specified in the facility safety analysis

are not exceeded. The safety analysis process will estimate radioactive and toxic source terms

and specify barrier integrity in terms of net leak rates to meet DOE-STD-6002-96 requirements

for exposure to on-site workers and the public during normal and off-normal events, including

design-basis events. Releases of hazardous materials postulated to occur as a result of design-

basis events that would exceed DOE-STD-6002-96 release guidelines should be limited by

designing facilities such that at least one confinement barrier remains fully functional following

any credible event. (i.e., unfiltered/unmitigated releases of hazardous levels of such materials

should not be allowed following such events).

Fusion vacuum vessels are typically subject to complex and transient stresses and have

many penetrations, some of which are of large cross-sectional area. It is, therefore, unlikely that

the net leakage from such a complex vessel could approach that of a simple pressure vessel or