TSR Derivation

DOE-STD-1120-2005/Vol. 1

Once step-out criteria are satisfied, contractor verification of the condition and DOE notification

is necessary to allow the contractor to retire the control. When using this approach, the TSR

should (1) use explicit TSR definitions that define terms and conditions used in retiring controls;

(2) incorporate step-out conditions into LCO applicability statements; (3) provide administrative

controls that formalize the process for stepping out of a control, as well as further safety

measures necessary once a control is retired; and (4) provide TSR Bases that support the

established points for stepping out of controls.

There may be unanticipated situations in which a retired facility safety control is needed to

perform its past safety function. For example, if unknown dispersible radiological materials are

discovered during the course of a decommissioning activity, it may be necessary to reactivate the

building ventilation system to provide a confinement function. In these cases, the operability,

maintainability, reliability, and availability of the reactivated control should be verified prior to

placing the control back into service.

3.3.1 TSR Derivation

The derivation of controls within the DSA should be consistent with expectations provided in

Chapter 5 of DOE-STD-3009. This applies to the entire suite of TSR controls, including specific

administrative controls. This information may be integrated together with the presentation and

description of controls as described in the DSA. For example, the derivational basis for specific

administrative controls may consist of brief logic statements that can be presented in tabular

form along side the listing of such controls.

Where specific administrative controls are selected in lieu or support of an engineered feature,

the derivational basis should justify why administrative controls by themselves or in combination

with other systems provide adequate protection against the accident consequences. For

example, certain administrative controls such as combustible material limits or ignition source

controls may be necessary to supplement an existing fire sprinkler system that is unreliable. In

this case, derivation of the administrative control should include discussion of the specific

reliability issues associated with the sprinkler system and justify how the selected administrative

controls ensure adequate protection against fire hazards.

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