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Safety-Significant SSCs cont'd - doe-std-3009-94_cn3_3-30-060065
Preparation Guide for U
Worker Safety - doe-std-3009-94_cn3_3-30-060067

DOE-STD -3009-94
features/items that may require specific TSR coverage. Such features include
instrumentation designed to detect significant barrier degradation; equipment
that actuates or controls so as to reduce the likelihood of significant barrier
challenges; process variables controlled for that purpose; and active controls
that prevent criticality. Every control or indicator does not require specific
TSR coverage. Likewise, every design feature malfunction or abnormal
condition does not constitute a major barrier or facility safety basis
Significant challenges to the facility safety basis are typically those events
which have a genuine potential to seriously damage safety SSCs, require
actuation of safety SSCs not on line as part of normal operations, or approach
conditions TSR controls are designed to prevent. Significant barrier
degradation is generally considered to mean substantial loss of barrier function
resulting in significant hazardous material release to areas of personnel
occupancy, or the occurrence of highly energetic events with the potential to
damage multiple barriers. To further explore barrier degradation, consider a
glovebox containing a dissolver vessel. A leak from the dissolver would not
be a major degradation of overall confinement because:
It is a slow, low energy phenomenon where the primary vessel itself
remains intact.
The release is into another layer of confinement not occup ied by
Process upsets resulting in an eructation from the vessel would not be major
degradation either. Even small, vapor space deflagrations that rupture vessel
blowout ports would not be a major degradation if the glovebox itself would
not sustain significant damage.
In contrast, consider a large hydrogen deflagration or detonation that ruptures
the vessel and piping, drives debris through the glovebox structural elements,
and momentarily pressurizes the glovebox. This is a highly energetic e vent
and multiple barriers have been damaged allowing a potentially significant
release of hazardous material directly to occupied areas. Possible TSR
coverage could include the maximum hydrogen concentration limits or
requiring an air purge system to be functioning when the dissolver is operating.
TSRs may also be provided for safety management programs in the form of
TSR administrative controls to support adequate defense in depth. Such all-
encompassing TSRs should be used in lieu of individual TSRs for numerous
specific aspects of programs unless the control is significant to specific
accident risk reduction. These administrative controls, designated as SACs,
are addressed in the TSRs as limiting conditions for operation with
surveillance requirements, or as specific directive action AC in the
Administrative Controls section of the TSR. DOE Standard 1186 provides
additional guidance for implementing SACs in TSRs.
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