Structures, systems, and components (SSCs). Structures are elements that provide support or enclosure
such as buildings, free standing tanks, basins, dikes, and stacks. Systems are collections of components
assembled to perform a function such as piping; cable trays; conduit; or heating, ventilating and air
conditioning (HVAC). Components are items of equipment such as pumps, valves, relays, or elements of a
larger array such as computer software, lengths of pipe, elbows, or reducers.
System Design Description (SDD). An SDD describes the requirements and features of a system. It
identifies the requirements of structures, systems, and components, explains the bases for the requirements,
and describes the features of the system that are designed to meet those requirements.
Technical Review The technical review is the interdisciplinary process to confirm or substantiate the
technical adequacy of a proposed change and ensure that it does not substantially degrade safety margins.
Technical Safety Requirements (TSRs). TSRs are the limits, controls, and related actions that establish the
specific parameters and requisite actions for the safe operation of a nuclear facility and include, as
appropriate for the work and the hazards identified in the documented safety analysis for the facility: Safety
limits, operating limits, surveillance requirements, administrative and management controls, use and
application provisions, and design features, as well as a bases appendix. (10 CFR Part 830)
USQ review. A USQ review is a review of a situation (such as a proposed change or a newly identified
potential inadequacy of the safety bases) in accordance with the DOE-approved USQ process to determine
if the situation involves a USQ.
Unreviewed Safety Question (USQ). A situation involves a USQ when:
(1) The probability of the occurrence or the consequences of an accident or the malfunction of
equipment important to safety previously evaluated in the documented safety analysis could be
(2) The possibility of an accident or malfunction of a different type than any evaluated previously in
the documented safety analysis could be created;
(3) A margin of safety could be reduced; or
(4) The documented safety analysis may not be bounding or may be otherwise inadequate. (10 CFR
USQ Process. The Unreviewed Safety Question process is the mechanism used to keeping a safety basis
(1) Reviewing potential USQs,
(2) Reporting USQs to DOE, and
(3) Obtaining approval from DOE prior to taking any action that involves an
For hazard category 1, 2, and 3 nuclear facilities, the USQ process is approved by DOE and required to
meet the provisions of 10 CFR Part 830. (10 CFR Part 830)
Verification (design reconstitution). For the design reconstitution program, the process of checking that the
retrieved design information has been completely and accurately translated from the source documents.
Vital safety systems. Vital safety systems are safety-class systems, safety-significant systems, and other
systems that perform an important defense-in-depth safety function.
Walkdown. A visual inspection of facility structures, systems, and components to identify the as-found
physical configuration and any discrepancies with currently approved facility documentation.