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Operable aka Operability (opposite: inoperable) is defined as Technical Specifications (TS) system, subsystem, division, component, or device shall be OPERABLE or have OPERABILITY when it is capable of performing its specified safety function(s) and when all necessary attendant Instrumentation, controls, normal or emergency electrical power, cooling and seal water, lubrication, and other auxiliary equipment that are required for the system, subsystem, division, component, or device to perform its specified safety function(s) are also capable of performing their related support function(s).

The term "Functional" refers to non-TS systems/components.

Presumption of operability

The concept of presumption of operability

A TS SSC is presumed to be operable if the associated surveillance requirements (SR) have been met, unless there is a deficient condition associated with the SSC or its required and necessary support SSC.

The improved STS Bases for SR 3.0.1 state:

“Systems and components are assumed to be OPERABLE when the associated SRs have been met. Nothing in this Specification, however, is to be construed as implying that systems or components are OPERABLE when:
a. The systems or components are known to be inoperable, although still meeting the SRs;
b. The requirements of the Surveillance(s) are known to be not met between required Surveillance performances.”

Reasonable Expectation of Operability

Upon discovery of a deficient condition in which the presumption of operability is lost. A subsequent determination of operability should be based on the "reasonable expectation," from the evidence collected, that the SSC are capable of performing its specified safety function and that the operability determination will support that expectation. Reasonable expectation does not mean absolute assurance that the SSC are operable. The SSC may be considered operable when there is evidence that the possibility of failure of an SSC has increased, but not to the point of eroding confidence in the reasonable expectation that the SSC remains operable. The supporting basis for the reasonable expectation of SSC operability should provide a high degree of confidence that the SSC remain operable. It should be noted that the standard of "reasonable expectation" is a high standard, and that there is no such thing as an indeterminate state of operability; an SSC is either operable or inoperable.

The concepts of presumption of operability and reasonable expectation of operability are distinct and do not coexist.

Relationship of Operability and Technical Specifications


Per SR 3.0.1, if as TS SR is not met then the LCO is not met. If an LCO is not met (or SR is not met) does that mean a system/component is "inoperable"?

  • The opposite is true, if a component is inoperable then the LCO is not met.

The answer is that Operability is contingent on meeting its various obligations aka Specified Function/Specified Safety Function: The definition of operability refers to the capability to perform the specified safety function. The specified safety function of an SSC is that specified safety function(s) in the CLB for the facility. Not all SSC functions described in the CLB are specified safety functions required for operability.

Current Licensing Basis (CLB): The set of NRC requirements applicable to a specific plant for ensuring compliance with, and operation within, applicable NRC requirements and the plant-specific design basis over the life of that facility’s operating license. The set of NRC requirements applicable to a specific plant’s CLB include but are not limited to:

a. NRC regulations in 10 CFR Parts 2, 19, 20, 21, 26, 30, 40, 50, 51, 52, 54, 55, 70, 72, 73, and 100 and appendices thereto,
b. Commission Orders,
c. License Conditions,
d. Exemptions,
e. Technical Specifications, and
f. Plant-specific design basis information defined in 10 CFR 50.2 and documented in the most recent Updated Final Safety Analysis Report (UFSAR) (as required by 10 CFR 50.71).

Therefore, meeting Technical Specifications is a criteria for Operability.

Operability and Supported System relationship

LCO 3.0.6 is known as the non-cascading rule because the TS allows for a LCO for a support system to drive actions before going to other LCO affected (e.g, ESW cools EDG but you only enter the ESW LCO and not the EDG). It is important to note that systems/components are still inoperable even though you don't need to enter their LCO. The EDG is in fact inoperable when ESW is inoperable.

NRC inspection of Operability

IP 71111.15 is the module used to evaluate Operability assessments. Most times it is just done by the resident throughout the year while reviewing CAP or during the course of a PI&R sample by another inspector. The inspection procedure IP 71111.15 list 15 samples or up to 21 per year. If you look at any quarterly inspection report it will tend to list which samples where done that quarter.

Inspection findings would be labeled with this inspection procedure if they were discovered during the course of the investigation.