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DOE-STD -3009-94
of such preventive or mitigative functions (e.g., electrical power sources for
ventilation).
The total layers of defense in depth available are also key considerations in
designating safety-significant SSCs. If many effective barriers are available,
the significance of any one barrier is lim ited. If only one or two barriers can be
realistically counted on, their individual significance increases. Likewise, if
total hazardous material inventory is distributed over a hundred containers
(e.g., waste drum storage pad, plutonium storage vault), the failure of any one
container does not necessarily constitute a major uncontrolled hazardous
material release, depending on the nature of the material and the design
adequacy of the container. If all material is held in one container (e.g., 3000
gallon hydrogen fluoride storage tank), the failure of that container is of major
concern in controlling the release of hazardous material. In the case where
quantities of hazardous materials are being stored so that breached nuclear
material storage packages might result from facility accident conditions, the
containers themselves may need to be upgraded or another facility level
method (secondary containment or confinement) considered for defense- in-
depth.
A principle reason for designating such major features as safety-significant
SSCs is that they typically represent facility specific systems as opposed to
more generic systems. While all glovebox line facilities use zone systems of
ventilation for confinement, there is an enormous variation in the DOE
comple x with regard to specific design parameters such as number and types of
exhaust systems, means of flow control, etc. Accordingly, more detailed
descriptions of such equipment in a DSA is considered both appropriate and
necessary for Hazard Category 2 facilities. Such description would not
provide the same utility for relatively generic confinement items such as 55-
gallon waste drums. The need for designation as a safety-significant SSC
would also be superseded if that SSC was designated as a safety-class SSC in
accident analysis.
TSRs
Summarize those safety-significant SSCs, SACs and other aspects of defense
in depth that require TSR coverage. The scope of the TSR coverage is
determined by the degree to which barriers or the facility-safety basis are
seriously challenged.
Vital, passive components such as piping, vessels, supports, structures, and
containers would typically be considered design features. These components
are discussed in the Design Features Section of the TSR document. For
example, a glovebox is an obvious barrier to uncontrolled material release.
The windows, gloves, and cable/piping connectors are all necessary to
maintain the barrier, but do not specifically require operational limits or
administrative controls as contributors to defense in depth.
DOE G 423.1-1 provides basic screening criteria to identify defense-in-depth
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