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UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF INSPECTION AND ENFORCEMENT

Washington, D.C. 20555

INSPECTION AND ENFORCEMENT MANUAL

DI

PART 9900: TECHNICAL GUIDANCE

STANDARD TECHNICAL SPECIFICATIONS

STS SECTION 1, OPERABILITY

A. PURPOSE

To provide guidance on the definition of operable/operability as it is

stated in the Standard Technical Specifications and applied to limiting

conditions for operation, as provided in an NRR memorandum dated July 8,

1985.

B. BACKGROUND

The definition of operable/operability in the Standard Technical Specifications (STS) as applied to a system, subsystem, train, component, or device

being capable of performing its specified function(s) includes all neces-

- sary attendant instrumentation, controls, electrical power, cooling or seal

water, lubrication or other auxiliary equipment also being capable of performing their related support function(s). For electrical power systems

which are supplied power fromthe normal offsite power grid and the emergency diesel generator sets, the typical question has been whether either

or both of these sources must be operable to fulfill the support system

requirements with regard to the STS definition of operability.

By Generic Letter dated April 10, 1980, model technical specifications were

provided to all power reactor licensees for a new technical specification

to clarify the operability requirements for supporting electrical power

systems. However, questions continue to be posed with respect to other supporting systems on the proper interpretation of the definition of operable/

operability as applied to specific systems, subsystems, trains, components,

or devices.

The purpose of the following discussion is to set forth the principal criteria that facilitate a proper application of the STS definition of operbHe/operability as applied to systems and components which provide necessary support functions. These criteria also facilitate an understanding.

of the operability requirements for systems and component which are explicitly stated in technical specifications.

C. DISCUSSION

1. Principal Criteria. The following are the principal criteria for

technical specification operability requirements.

Issue Date: 05/12/86
a. The system* operability requirements should be consistent with

the safety analysis of specific design-bases events and regulatory requirements.

b The system operability requirements, including related regulatory requirements, may be waived as a consequence of specified

action statements.

c. Design-basis events are plant specific and regulatory requirements may have plant-specific considerations related to technical specification operability requirements.

d. The system operability requirements that are based on safety

analysis of specific design-basis events for one mode or condition of operation may not be the same for all modes or conditions of operation.

e. The system operability requirements extend to necessary support

systems regardless of the existence or absence of support system

requirements.

f. The operability of necessary support systems includes regulatory

requirements. It does not include consideration of the occurence multiple (simultaneous) design basis events.

2. Support Function. Technical specifications specify Limiting Condition for Operation (LCO) for those systems, subsystems, trains,

components or devices that directly provide the capability to mitigate the consequences of design-basis events as well as generally

specifying an LCO for those that indirectly provide this capability

as a support function. Support functions are defined to include all

necessary attendant instrumentation, controls, electrical power,

cooling or seal water, lubrication or other auxiliary equipment that

is required to perform a supporting function. Because the technical

specifications do not directly specify an LCO for many items that

perform supporting functions, a knowledge of the plant design basis

is essential to determine which support functions can affect plant

operability.

Since nuclear plants were not all designed and built in conformance to the same regulatory requirements, the design-basis events

addressed in FSARs include differences depending on requirements

which existed at the time the construction permit and/or operating

license was issued. However, some new regulatory requirements have

been issued that are applicable to all plants while others have limýited applicabilty. Thus, FSARs as well as applicable regulatory

,±equirements include information which is essential to the definition of design basis events for a facility.

*The term system is used here to include a subsystem, train, component or

device as may be applicable to the STS operability requirements.

issue Date: 05/12 /86 - _ 9900 STS Section 1
3. Applicable Operating Conditions. The LCOs specify operability requirements in terms of plant operating modes or conditions. For the

majority of the specifications, redundant systems or components are

required to be operable to ensure that the requirements of the single-failure criterion are satisfied. When a system or component is

inoperable, actions are required to restore the system or component

to operable status in specified time limits or to place the plant in

a mode or condition for which .the LCO no longer applies. The LCO

requirements for some operating modes or conditions only require one

rather than two redundant systems or components to be operable.

Although the operability requirements are specified in terms of operating modes or conditions, they are chosen to be consistent with

the analysis of design-basis events. For many events, the analysis

is limited to consideration of the power mode of operation with emphasis on full-power operation where conditions present the greatest

challenge to safety limits. For some events, consideration is given

to 25%-or zero-power conditions if these cases represent a more limiting condition with respect to safety limits. Often only the

bounding, i.e. , most limiting, conditions are presented in FSAR

safety analysis.

With respect to LCO requirements for conditions or modes other than

power operation, the requirements have been generally based on engineering judgment rather than specific event analysis. The ECCS

is typical of those systems and components for which the LCO requirements for operability, other than the power mode of operation,

have been based on engineering judgment for events that are classified as accidents and antici'pated transients.

For those design basis events for which an analysis is provided

during the power mode of operation, the technical specifications do

allow exceptions to the requirements of the General Design Criteria

(GDC) for limited periods of time. For example systems or components are allowed to be out-of-service for testing or maintenance

for specified time intervals. During such-times the requirements of

the single failure criterion as specified in the GDC for specific

systems may not be satisfied.

For some events, particularly those due to natural phenomena such as

earthquakes, floods, or storms, the safety considerations relate to

the capability to'shut down the plant and maintain it in a safe condition. Generally the operability requirements of systems or components are based on the modes or conditions for which these systems

or components are effective to accomplish this function and may in-

.clude essentially all operating modes. Fires, missiles, and accidents at nearby locations are another group of events for which similar requirements may apply.

Design basis events are analyzed to demonstrate that a plant can be

operated without undue risk to public health and safety. Other than

as specified by a regulatory requirement, each design basis event is

taken as an individual case and not in combination with other design

basis events. For those systems for which the design criteria specify that the safety function shall be provided with either onsite or

offsite power system operation assuming the other is unavailable, a

situation exists where the event of a loss of offsite power is con9q00 STS Section I - 3 - Issue Date: 05/12/86
sidered simultaneously with an event in which the safety function of

such systems is required.

Safety-related structures, systems, and components are designed to

(1) remain functional during a Safe Shutdown Earthquake (SSE), (2)

ensure the integrity of the reactor coolant pressure boundary, and

(3) to have the capability to shut down the reactor and maintain it

in a safe condition or the capability to mitigate the consequences

of accidents. However, as a design-basis event, the SSE is not

assumed to occur simultaneously with postulated accidents.

D. CONCLUSION

Many systems and components perform dual-function roles with regard to

accident mitigation and for events for which safe plant shutdown is

required. The correct application of operability requirements for these

systems and components requires additional reliance on a knowledge of

design basis events. Thus, it is essential for the proper application of

the technical specifications operability requirements, to know the applicable design-basis events for a facility.

For the reactor-trip and engineered safety features actuations systems, the

technical specifications generally indicate specific modes or conditions

for which automatic features of these systems are required to be operable.

For many systems, manual initiation capabilities are provided in addition

to ,automatic features. When the technical specifications operability

requirements are stated in terms of overall system requirements, specific

control features such as automatic or manual may not be specifically

addressed in the operability requirements. Further, in many cases the FSAR

may only address bounding analysis, typically for the power mode of operation, such that a specific design basis is not stated for other modes of

operation. In such cases, it is incorrect to assume that the safety

analysis assumptions for a design basis event are applicable to all other

modes of operation. From the standpoint of safety, the technical specifications set forth the limiting conditions for operation and actions which

are appropriate for modes of operation other than those addressed by

specific design basis events analysis or applicable regulatory requirements.

E. REFERENCE

The guidance provided in this directive was extracted from a memorandum

from Dennis M. Crutchfield, Assistant Director for Safety Assessment, NRR,

for H;' Thompson, et al., dated July 8, 1985, subject: Technical SpecificationklOperability Requirements. The complete memorandum is in the Document

Control System (DCS microfiche #67973-003).

END

Issue Date: 05/12/86 -4 - 9900 STS Section 1