United States Nuclear Regulatory Commission - Protecting People and the Environment

Clarification of the Term "Operable" as It Applies to Single Failure Criterion for Safety Systems Required by TS (Generic Letter 80-30)



GL80030 

                              UNITED STATES 
                      NUCLEAR REGULATORY COMMISSION 
                          WASHINGTON, D.C. 20555 

                              April 10, 1980 

ALL POWER REACTOR LICENSEES 

Gentlemen: 

It has recently come to our attention that there may be some 
misunderstanding regarding the use of the term OPERABLE as it applies to the 
single failure criterion for safety systems in power reactors. The purpose 
of this letter is to clarify the meaning of this term and to request 
licensees to take specific actions to assure that it is appropriately 
applied at their-facilities. IE Information Notice No. 79-35, "Control of 
Maintenance and Essential Equipment" also contained information on this 
subject. 

The NRC's Standard Technical Specifications (STS) were formulated to 
preserve the single failure criterion for systems that are relied upon in 
the safety analysis report. By and large, the single failure criterion is 
preserved by specifying Limiting Conditions for Operation (LCOs) that 
require all redundant components of safety related systems to be OPERABLE. 
When the required redundancy is not maintained, either due to equipment 
failure or maintenance outage, action is required, within a specified time, 
to change the operating mode of the plant to place it in a safe condition. 
The specified time to take action, usually called the equipment 
out-of-service time, is a temporary relaxation of the single failure 
criterion, which, consistent with overall system reliability considerations, 
provides a limited time to fix equipment or otherwise make it OPERABLE. If 
equipment can be returned to OPERABLE status within the specified time, 
plant shutdown is not required. 

LCOs are specified for each safety related system in the plant, and with few
exceptions, the ACTION statements address single outages of components, 
trains or subsystems. For any particular system, the LCO does not address 
multiple outages of redundant components, nor does it address the effects of
outages of any support systems - such as electrical power or cooling water - 
that are relied upon to maintain the OPERABILITY of the particular system. 
This is because of the large number of combinations of these types of 
outages that are possible. Instead, the STS employ general specifications 
and an explicit definition of the tem OPERABLE to encompass all such cases. 
These provisions have been formulated to assure that no set of equipment 
outages would be allowed to persist that would result in the facility being 
in an unprotected condition. These specifications are contained in the 
enclosed Model Technical Specifications. Illustrative examples of how these 
specifications apply are contained, in the associated Bases. 
.

                                  - 2 - 

Because of the importance of assuring safety system availability, the staff 
has concluded that all facility technical specifications should contain 
these requirements, and that appropriate procedures should be implemented to 
assure that the necessary records, such as plant logs or similar documents, 
are reviewed to determine compliance with these specifications (1) promptly 
upon discovering a component, train, or subsystem to be inoperable, and (2) 
prior to removing a component from service. 

Therefore, we request that you (1) submit proposed changes to your technical
specifications, within 30 days, that incorporate the requirements of the 
enclosed Model Technical Specifications, and (2) implement the above 
described procedures to assure compliance with your proposed changes within 
30 days thereafter. 

With regard to technical specification changes, we recognize that the 
terminology used in the enclosed Model Technical Specifications may not 
directly apply to plants without STS, therefore the OPERATIONAL MODE or 
CONDITION definitions are also included in the enclosure. If you do not have
STS you should modify the terminology to make it consistent with your 
particular facility technical specifications. 

If you have any questions, please contact us. 

                                   Sincerely, 


                                   Darrell G. Eisenhut, Acting Director 
                                   Division of Operating Reactors 
                                   Office of Nuclear Reactor Regulation 

Enclosure: 
Model Technical Specifications 
.

                                                              Enclosure 1 

                      MODEL TECHNICAL SPECIFICATIONS 
                        PRESSURIZED WATER REACTORS 

1.0  DEFINITIONS 
OPERABLE - OPERABILITY 

1.6 A system, subsystem, train, component or device shall be OPERABLE or 
have OPERABILITY when it is capable of performing its specified function(s).
Implicit in this definition shall be the assumption that all necessary 
attendant instrumentation, controls, normal and emergency electrical power 
sources, cooling or seal water, lubrication or other auxiliary equipment 
that are required for the system, subsystem, train, component or device to 
perform its function(s) are also capable of performing their related support
function(s). 

3/4 LIMITING CONDITIONS FOR OPERATION (GENERAL) 

3/4.0 APPLICABILITY 

LIMITING CONDITION FOR OPERATION 

3.0.3 In the event a Limiting Condition for Operation and/or associated 
ACTION requirements cannot be satisfied because of circumstances in excess 
of those addressed in the specification, the unit shall be placed in at 
least HOT STANDBY within 1 hour, in at least HOT SHUTDOWN within the next 6 
hours, and in at least COLD SHUTDOWN within the following 30 hours unless 
corrective measures are completed that permit operation under the 
permissible ACTION statements for the specified time interval as measured 
from initial discovery or until the reactor is placed in a MODE in which the 
specification is not applicable. Exceptions to these requirements shall be 
stated in the individual specifications. 

3.0.5 When a system, subsystem, train, component or device is determined to 
be inoperable solely because its emergency power source is inoperable, or 
solely because its normal power source is inoperable, it may be considered 
OPERABLE for the purpose of satisfying the requirements of its applicable 
Limiting Condition for Operation, provided: 1) its corresponding normal or 
emergency power source is OPERABLE; and (2) all of its redundant system(s), 
subsystem(s), train(s), component(s) and device(s) are OPERABLE, or likewise
satisfy the requirements of this specification. Unless both conditions (1) 
and (2) are satisfied, the unit shall be placed in at least HOT STANDBY 
within 1 hour, in at least HOT SHUTDOWN within the next 6 hours, and in at 
least COLD SHUTDOWN within the following 30 hours. This specification is not
applicable in MODES 5 or 6. 
.

                                  - 2 - 

3/4.0 APPLICABILITY 

BASES 

3.0.3 This specification delineates the ACTION to be taken for circumstances
not directly provided for in the ACTION statements and whose occurrence 
would violation the intent of the specification. For example, Specification 
3.5.1 requires each Reactor Coolant System accumulator to be OPERABLE and 
provides explicit ACTION requirements if one accumulator is inoperable. 
Under the terms of Specification 3.0.3, if more than one accumulator is 
inoperable, the unit is required to be in at least HOT STANDBY within 1 hour 
and in at least HOT SHUTDOWN within the following 6 hours. As a further 
example, Specification 3.6.2.1 requires two Containment Spray Systems to be 
OPERABLE and provides explicit ACTION requirements if one spray system is 
inoperable: Under the terms of Specification 3.0.3, If both of the required 
Containment Spray Systems are inoperable, the unIt is required to be in at 
least HOT STANDBY within 1 hour, In at least HOT SHUTDOWN within the 
following 6 hours and in at least COLD SHUTDOWN In the next 30 hours. It Is 
assumed that the unit is brought to the required MODE within the required 
times by promptly Initiating and carrying out the appropriate ACTION 
statement. 

3.0.5 This specification delineates what additional conditions must be 
satisfied to permit operation to continue, consistent with the ACTION 
statements for power sources, when a normal or emergency power source is not
OPERABLE. It specifically prohibits operation when one division is 
inoperable because its normal or emergency power source is inoperable and a 
system, subsystem, train, component or device in another division is 
inoperable for another reason. 

The provisions of this specification permit the ACTION statements associated
with individual systems, subsystems, trains, components, or devices to be 
consistent with the ACTION statements of the associated electrical power 
source. It allows operation to be governed by the time limits of the ACTION 
statement associated with the Limiting Condition for Operation for the 
normal or emergency power source, not the individual ACTION statements for 
each system, subsystem, train, component or device that is determined to be 
inoperable solely because of the inoperability of its normal or emergency 
power source. 

For example, Specification 3.8.1.1 requires in part that two emergency 
diesel generators be OPERABLE. The ACTION statement provides for a 72 hour 
out-of-service time when one emergency diesel generator is not OPERABLE. If 
the definition of OPERABLE were applied without consideration of 
Specification 3.0.5, all systems, subsystems, trains, components and devices 
supplied by the inoperable emergency power source would also be inoperable. 
This would dictate invoking the applicable ACTION statements for each of the 
applicable Limiting Conditions for Operation. However, the provisions of 
Specification 3.0.5 permit the time limits for continued operation to be 
consistent with the ACTION statement for the inoperable 
.

                                  - 3 - 

emergency diesel generator instead, provided the other specified conditions 
are satisfied. In this case, this would mean that the corresponding normal 
power source must be OPERABLE, and all redundant systems, subsystems, 
trains, components, and devices must be OPERABLE, or otherwise satisfy 
Specification 3.0.5 (i.e., be capable of performing their design function 
and have at least one normal or one emergency power source OPERABLE). If 
they are not satisfied, shutdown is required in accordance with this 
specification. 

As a further example Specification 3.8.1.1 requires in part that two 
physically independent circuits between the offsite transmission network and
the onsite Class IE distribution system be OPERABLE. The ACTION statement 
provides a 24 hour out-of-service time when both required offsite circuits 
are not OPERABLE. If the definition of OPERABLE were applied without 
consideration of Specification 3.0.5, all systems, subsystems, trains, 
components and devices supplied by the inoperable normal power sources, both
of the offsite circuits, would also be inoperable. This would dictate 
invoking the applicable ACTION statements for each of the applicable LCOs. 
However, the provisions of Specification 3.0.5 permit the time limits for 
continued operation to be consistent with the ACTION statement for the 
inoperable normal power sources instead, provided the other specified 
conditions are satisfied. In this case, this would mean that for one 
division the emergency power source must be OPERABLE (as must be the 
components supplied by the emergency power source) and all redundant 
systems, subsystems, trains, components and devices in the other division 
must be OPERABLE, or likewise satisfy Specification 3.0.5 (i.e., be capable 
of performing their design functions and have an emergency power source 
OPERABLE). In other words, both emergency power sources must be OPERABLE and
all redundant systems, subsystems, trains, components and devices in both 
divisions must also be OPERABLE. If these conditions are not satisfied, 
shutdown is required in accordance with this specification. 

In MODES 5 or 6 Specification 3.0.5 is not applicable, and thus the 
individual ACTION statements for each applicable Limiting Condition for 
Operation in these MODES must be adhered to. 
.

                    DEFINITION OF WESTINGHOUSE PWR  
                            OPERATIONAL MODES  

                      REACTIVITY             % RATED        AVERAGE COOLANT 
     MODE           CONDITION, Keff       THERMAL POWER*      TEMPERATURE 

1. POWER OPERATION       => 0.99             => 5%             => 350F 

2. STARTUP               => 0.99             <  5%             => 350F 

3. HOT STANDBY           <  0.99             0                 => 350F 

4. HOT SHUTDOWN          <  0.99             0                 350F 
                                                               > Tavg > 
                                                               200F 

5. COLD SHUTDOWN         <  0.99             0                 =< 200F 

6. REFUELING**           =< 0.95             0                 =< 140F 

*Excluding decay heat.
**Reactor vessel head unbolted or removed and fuel in the vessel. 
.

               DEFINITION OF COMBUSTION ENGINEERING PWR  
                            OPERATIONAL MODES 

                    REACTIVITY          % OF RATED          AVERAGE COOLANT 
OPERATIONAL MODE   CONDITION, Keff   THERMAL POWER*           TEMPERATURE 

1. POWER OPERATION  => 0.99              >  5%                 => 300F 

2. STARTUP          => 0.99              =< 5%                 => 300F 

3. HOT STANDBY       < 0.99                 0                  => 300F 

4. HOT SHUTDOWN      < 0.99                 0                  300F 
                                                               > Tavg 
                                                               200F 

5. COLD SHUTDOWN     < 0.99                 0                  < 200F 

6. REFUELING**      =< 0.95                 0                  =< 140F 

*Excluding decay heat.
**Reactor vessel head unbolted or removed and fuel in the vessel. 
.

                   DEFINITION OF BABCOCK & WILCOX PWR 
                            OPERATIONAL MODES 

                    REACTIVITY          % OF RATED          AVERAGE COOLANT 
OPERATIONAL MODE   CONDITION, Keff   THERMAL POWER*           TEMPERATURE 

1. POWER OPERATION  => 0.99              >  5%                 => 305F 

2. STARTUP          => 0.99              =< 5%                 => 305F 

3. HOT STANDBY       < 0.99                 0                  => 305F 

4. HOT SHUTDOWN      < 0.99                 0                  305F 
                                                               > Tavg 
                                                               200F 

5. COLD SHUTDOWN     < 0.99                 0                  < 200F 

6. REFUELING**      =< 0.95                 0                  =< 140F 

*Excluding decay heat.
**Reactor vessel head unbolted or removed and fuel in the vessel. 
.

                                                              Enclosure 2 

                      MODEL TECHNICAL SPECIFICATIONS 
                          BOILING WATER REACTORS 

1.0 DEFINITION 

OPERABLE - OPERABILITY 

1.20 A system, subsystem, train, component or device shall be OPERABLE or 
have OPERABILITY when it is capable of performing its specified function(s).
Implicit in this definition shall be the assumption that all necessary 
attendant instrumentation, controls, normal and emergency electrical power 
sources, cooling or seal water, lubrication or other auxiliary equipment 
that are required for the system, subsystem, train, component or device to 
perform its function(s) are also capable of performing their related support
function(s). 

3/4 LIMITING CONDITIONS FOR OPERATION (GENERAL) 

3/4.0 APPLICABILITY 

LIMITING CONDITION FOR OPERATION 

3.0.3 In the event a Limiting Condition for Operation and/or associated 
ACTION requirements cannot be satisfied because of circumstances in excess 
of those addressed in the specification, the unit shall be placed in at 
least HOT SHUTDOWN within 6 hours and in COLD SHUTDOWN within the following 
30 hours unless corrective measures are completed that permit operation 
under the permissible discovery or until the reactor is placed in an 
OPERATIONAL CONDITION in which the specification is not applicable. 
Exceptions to these requirements shall be stated in the individual 
specifications. 

3.0.5 When a system, subsystem, train, component or device is determined to 
be inoperable soley because its emergency power source is inoperable, or 
solely because its normal power source is inoperable, It may be considered 
OPERABLE for the purpose of satisfying the requirements of its applicable 
Limiting Condition for Operation, provided: (1) its corresponding normal or 
emergency power source is OPERABLE, and (2) all of its redundant system(s), 
subsystem(s), train(s), component(s) and device(s) are OPERABLE, or likewise
satisfy the requirements of this specification. Unless both conditions (1) 
and (2) are satisfied, the unit shall be placed in at least HOT SHUTDOWN 
within 6 hours, and in at least COLD SHUTDOWN within the following 30 hours.
This specification is not applicable in Conditions 4 or 5. 
.

                                  - 2 - 

3/4.0 APPLICABILITY 

BASES 

3.0.3 This specification delineates the ACTION to be taken for circumstances
not directly provided for in the ACTION statements and whose occurrence 
would violate the intent of the specification. For example, Specification 
3.7.2 calls for two control room emergency filtration subsystems to be 
OPERABLE and provides explicit ACTION requirements if one subsystem is 
inoperable. Under the terms of Specification 3.0.3, if both of the required 
subsystems are inoperable, the unit is to be in at least HOT SHUTDOWN within 
6 hours and in COLD SHUTDOWN within the next 30 hours. As a further example, 
Specification 3.6.6.1 requires two primary containment hydrogen recombiner 
systems to be OPERABLE and provides explicit ACTION requirements if one 
recombiner system is inoperable. Under the terms of Specification 3.0.3, if 
both of the required systems are inoperable, the unit is to be in at least 
HOT SHUTDOWN within 6 hours. It is assumed that the unit is brought to the 
required OPERATIONAL CONDITION within the required times by promptly 
initiating and carrying out the appropriate ACTION statement. 

3.0.5 This specification delineates what additional conditions must be 
satisfied to permit operation to continue, consistent with the ACTION 
statements for power sources, when a normal or emergency power source is not
OPERABLE. It specifically prohibits operation when one division is 
inoperable because its normal or emergency power source is inoperable and a 
system, subsystem, train, component or device in another division is 
inoperable for another reason. 

The provisions of this specification permit the ACTION statements associated
with individual systems, subsystems, trains components or devices to be 
consistent with the ACTION statements of the associated electrical power 
source. It allows operation to be governed by the time limits of the ACTION 
statement associated with the Limiting Condition for Operation for the 
normal or emergency power source, not the individual ACTION statements for 
each system, subsystem, train, component or device that is determined to be 
inoperable solely because of the inoperability of its normal or emergency 
power source. 

For example, Specification 3.8.1.1 requires in part that all three emergency
diesel generators be OPERABLE. The ACTION statement provides for a 72 hour 
out-of-service time when emergency diesel generator (1A) or (1B) is not 
OPERABLE. If the definition of OPERABLE were applied without consideration 
of Specification 3.0.5. all systems, subsystems, trains, components and 
devices supplied by the inoperable emergency power source, diesel generator 
(1A) or (1B), would also be inoperable. This would dictate invoking the 
applicable ACTION statements for each of the applicable Limiting Conditions 
for Operation. However, the provisions of Specification 3.0.5 permit the 
time limits for continued operation to be consistent with the ACTION 
statement for the inoperable emergency diesel generator instead, provided 
the other specified conditions are satisfied. If they are not satisfied, 
shutdown is required in accordance with this specification. 
.

                                  - 3 - 

As a further example, Specification 3.8.1.1 requires in part that two 
physically independent circuits between the offsite transmission network and
the onsite Class IE distribution system be OPERABLE. The ACTION statement 
provides a 24 hour out-of-service time when both required offsite circuits 
are not OPERABLE. If the definition of OPERABLE were applied without 
consideration of Specification 3.0.5, all systems, subsystems, trains, 
components and devices supplied by the inoperable normal power sources, both
of the offsite circuits, would also be inoperable. This would dictate 
invoking the applicable ACTION statements for each of the applicable LCOs. 
However, the provisions of Specification 3.0.5 permit the time limits for 
continued operation to be consistent with the ACTION, statement for the 
inoperable normal power sources instead, provided the other specified 
conditions are satisfied. In this case, this would mean that for one 
division the emergency power source must be OPERABLE (as must be the 
components) supplied by the emergency power source) and all redundant 
systems, subsystems, trains, components and devices in the other division 
must be OPERABLE, or likewise satisfy Specification 3.0.5 (i.e., be capable 
of performing their design functions and have an emergency power source 
OPERABLE). In other words, both emergency power sources (1A) and (1B) must 
be OPERABLE and all redundant systems, subsystems, trains, components and 
devices In both divisions must also be OPERABLE. If these conditions are not
satisfied, shutdown is required in accordance with this specification. 

In Condition 4 or 5 Specification 3.0.5 is not applicable, and thus the 
individual ACTION statements for each applicable Limiting Condition for 
Operation in these Conditions must be adhered to. 
.

                           DEFINITION OF BWR 
                          OPERATIONAL CONDITIONS 

                         MODE SWITCH                   AVERAGE REACTOR 
CONDITION                  POSITION                 COOLANT TEMPERATURE 

1. POWER OPERATION       Run                           Any temperature 

2. STARTUP               Startup/Hot Standby           Any temperature 

3. HOT SHUTDOWN          Shutdown                      > 212F 

4. COLD SHUTDOWN         Shutdown                      <= 212F 

5. REFUELING*            Shutdown or Refuel**          <= 212F  

* Reactor vessel head unbolted or removed and fuel in the vessel.
**See Special Test Exception 3.10.3  

Page Last Reviewed/Updated Monday, June 17, 2013