ML100550649

Developmental Revision B - Technical Requirements Manual Bases B 3.8 - Electrical Power Systems

ML100550649
Person / Time
Site:	Watts Bar
Issue date:	02/02/2010
From:	Tennessee Valley Authority
To:	Office of Nuclear Reactor Regulation
References
Download: ML100550649 (19)

Text

Isolation Devices B 3.8.1 (continued)

Watts Bar - Unit 2 B 3.8-1 Technical Requirements (developmental)

A B 3.8 ELECTRICAL POWER SYSTEMS B 3.8.1 Isolation Devices BASES BACKGROUND The onsite Class 1E AC and DC electrical power distribution system is divided by trains into two redundant and independent AC and DC electrical power distribution subsystems. Each AC and DC electrical power distribution subsystem is comprised of 6.9kV AC shutdown boards, 480V AC shutdown boards, associated motor control centers, and 120V AC power distribution panels, 120V AC vital buses, and 125V DC vital buses. Two trains (or subsystems) are required for safety function redundancy; any one train provides safety function, but without worst-case single-failure protection.

Because of the safety significance of the Class 1E AC and DC electrical power distribution subsystems and the equipment that they supply, unique requirements for OPERABILITY are imposed on these subsystems beyond those requirements applicable to non-qualified AC and DC distribution subsystems. As such, 1E buses must be protected from faults that could occur on loads not included as part of the Class 1E system, associated nonqualified cables routed in Class 1E cable trays or nonqualified cables insufficiently separated from Class 1E cables. Circuit breakers actuated by fault currents are used as isolation devices in this plant to detect and isolate faults. The OPERABILITY of these circuit breakers ensures that the Class 1E buses will be protected in the event of faults in nonqualified loads powered by the buses, located in associated nonqualified cables routed in Class 1E cable trays or in nonqualified cables insufficiently separated from Class 1E cables.

APPLICABLE SAFETY ANALYSES The initial conditions of design basis transient and accident analyses in FSAR Chapter 6, "Engineered Safety Feature," and Chapter 15, "Accident Analyses" (Ref. 1) assume ESF Systems are OPERABLE. The Class 1E AC and DC electrical power distribution systems are designed to provide sufficient capacity, capability, redundancy, and reliability to ensure the availability of necessary power to ESF Systems so that the fuel, Reactor Coolant System (RCS) and containment design limits are not exceeded. These limits are discussed in more detail in the Bases for Technical Specifications 3.2 (Power Distribution Limits), 3.4 (Reactor Coolant System), and 3.6 (Containment Systems).

Isolation Devices B 3.8.1 BASES (continued)

Watts Bar - Unit 2 B 3.8-2 Technical Requirements (developmental)

B APPLICABLE SAFETY ANALYSES (continued)

The OPERABILITY of the AC and DC electrical power distribution systems is consistent with the initial assumptions of the accident analyses (Ref. 1) and is based upon meeting the design basis of the plant. This includes maintaining at least one train of the onsite or offsite AC electrical power sources, DC electrical power sources, and associated distribution systems OPERABLE during accident conditions in the event of:

a.

An assumed loss of all offsite power or all onsite AC electrical power; and

b.

A worst-case single failure.

Isolation devices help ensure the OPERABILITY of Class 1E AC and DC electrical power distribution systems by protecting them from faults on the non-Class 1E portion of the distribution system, on associated nonqualified cables routed in Class 1E cable trays, or on nonqualified cables insufficiently separated from Class 1E cables. However, these devices are not a structure, system, or component that is part of the primary success path and which actuates to mitigate a DBA or transient that either assumes a failure of or presents a challenge to the integrity of a fission product barrier.

TR TR 3.8.1 requires that all circuit breakers actuated by fault currents that are used as isolation devices protecting Class 1E buses from non-qualified loads, associated circuits or insufficiently separated cables shall be OPERABLE. These breakers are identified on Drawing Series 45A710 (Ref. 3). This Technical Requirement satisfies testing specified in Sections 8.3.3.3 (2) and 8.3.3.3 (3) of the Safety Evaluation Report (Ref. 4). The OPERABILITY of these devices helps ensure that the Class 1E subsystem will be protected from faults that occur on the non-Class 1E portion of the distribution system.

APPLICABILITY The Class 1E AC and DC electrical distribution systems are required to supply power to those systems necessary to mitigate the consequences of DBAs or transients that could occur in MODES 1, 2, 3, or 4. Isolation devices are therefore required to protect the Class 1E distribution systems in these MODES.

Isolation Devices B 3.8.1 BASES (continued)

Watts Bar - Unit 2 B 3.8-3 Technical Requirements (developmental)

A ACTIONS A.1, A.2.1, and A.2.2 With one or more of the required circuit breakers inoperable, the Class 1E distribution system is not isolated from faults on non-Class 1E portions of the distribution system, on non-Class 1E associated cables routed in Class 1E cable trays, or on Non-Class 1E cables insufficiently separated from Class 1E cables.

Action must be taken to restore this isolation. One possible solution is to restore the circuit breaker(s) to OPERABLE status. If this cannot be done, the isolation can be achieved manually by tripping or removing the inoperable circuit breaker(s). Removing the inoperable breaker(s) ensures that they will not be inadvertently closed before they can be restored to OPERABLE status. The Completion Time of 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> takes into consideration the low probability of a fault occurring on the distribution system, on an associated non-Class 1E circuit or on an insufficiently separated non-Class 1E cable, concurrent with an event requiring the safety systems supplied by the Class 1E system. It also represents a reasonable time to repair or trip (or remove) the inoperable circuit breaker(s).

To ensure that the inoperable circuit breaker(s) are not inadvertently re-energized before they are returned to OPERABLE status, it is necessary to periodically verify that they remain tripped or removed. The period of 7 days takes into consideration the unlikelihood that a plant operation or maintenance activity would result in the re-energization of these breaker(s) from the de-energized condition.

B.1 and B.2 If the Required Action and associated Completion Time of Condition A cannot be met, the Class 1E system remains unprotected from faults on non-Class 1E portions of the distribution system, on non-Class 1E associated cables routed in Class 1E cable trays or on non-Class 1E cables insufficiently separated from Class 1E cables. Since this condition cannot be allowed for an extended period of time, it is necessary to place the plant in a condition where the isolation devices are not required to be OPERABLE. This is done by placing the plant in MODE 3 in 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and then in MODE 5 in the next 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />. The allowed Completion Times are reasonable, based on operating experience, to reach the required plant conditions from full power conditions in an orderly manner and without challenging plant systems.

Isolation Devices B 3.8.1 BASES (continued)

Watts Bar - Unit 2 B 3.8-4 Technical Requirements (developmental)

A TECHNICAL SURVEILLANCE REQUIREMENTS TSR 3.8.1.1 This surveillance requires the performance of a functional test on a representative sample of 10% of each type of molded-case circuit breaker used as an isolation device. This sample size is sufficiently large to represent the actual failure distribution within the whole population of circuit breakers of a given type used in the plant. If there are any failure mechanisms that could affect the OPERABILITY of the circuit breaker(s) they are likely to have occurred in the sample tested. The 18 month Frequency takes into consideration the infrequent operation of the breakers and their correspondingly low failure rate. The Surveillance is augmented by three Notes. The first Note states that the breakers shall be selected for testing on a rotating basis. This ensures that all of the breakers will eventually be tested and those failures that may not have been discovered in the initial 10% samples will eventually be discovered.

The second Note describes the functional test procedure and the response to be verified to ensure OPERABILITY.

The third Note states that for each molded case circuit breaker found inoperable during functional tests an additional representative sample of 10% of the defective type shall be functionally tested until no more failures are found or all of that type have been functionally tested. This helps to ensure that a failure discovered in the representative sample was not caused by a failure mechanism that could systematically affect other breakers in the overall population of breakers of the same type.

TSR 3.8.1.2 This surveillance requires the performance of a functional test on a representative sample of 10% of each type of electrically-operated circuit breaker used as an isolation device. This sample size is sufficiently large to represent the actual failure distribution within the whole population of circuit breakers of a given type used in the plant. If there are any failure mechanisms that could affect the OPERABILITY of the circuit breaker(s), they are likely to have occurred in the sample tested. The 18 month Frequency takes into consideration the infrequent operation of the breakers and their correspondingly low failure rate.

The Surveillance is augmented by three Notes. The first Note states that the breakers shall be selected for testing on a rotating basis. This ensures that all of the breakers will eventually be tested and those failures that may not have been discovered in the initial 10% samples will eventually be discovered. The second Note describes the functional test procedure and the response to be verified to ensure OPERABILITY.

Isolation Devices B 3.8.1 BASES (continued)

Watts Bar - Unit 2 B 3.8-5 Technical Requirements (developmental)

A TECHNICAL SURVEILLANCE REQUIREMENTS TSR 3.8.1.2 (continued)

The third Note states that for each electrically-operated circuit breaker found inoperable during functional tests an additional representative sample of 10% of the defective type shall be functionally tested until no more failures are found or all of that type have been functionally tested.

This helps to ensure that a failure discovered in the representative sample was not caused by a failure mechanism that could systematically affect other breakers in the overall population of breakers of the same type.

TSR 3.8.1.3 This surveillance requires that the performance of a CHANNEL CALIBRATION of all protective relays associated with medium voltage (6.9 kV) isolation overcurrent devices. A CHANNEL CALIBRATION assures that the relays will be able to detect overcurrent conditions on the non-Class 1E loads. The Frequency of 18 months is consistent with the typical industry refueling cycle.

TSR 3.8.1.4 This surveillance requires the performance of an integrated system functional test which verifies that the relays and associated medium voltage (6.9 kV) circuit breakers function as designed to isolate fault currents. An integrated test assures that the individual elements of the protection scheme, the relays, breakers and other control circuits, interact as designed.

The surveillance has been modified by a Note stating that if a failure is discovered in the integrated functional test, an additional representative sample of at least 10% of all the circuit breakers of the inoperable type shall also be tested to assure that there is no common cause failure mechanism that could systematically affect all breakers of a given type.

The Frequency of 18 months coincides with the typical industry refueling cycle.

Isolation Devices B 3.8.1 BASES Watts Bar - Unit 2 B 3.8-6 Technical Requirements (developmental)

B TECHNICAL SURVEILLANCE REQUIREMENTS (continued)

TSR 3.8.1.5 This surveillance requires the inspection of each circuit breaker and the performance of procedures prepared in conjunction with the manufacturer's recommendations. By performance of recommended maintenance, the likelihood for the circuit breakers to become inoperable can be minimized. The 72 months periodicity for Class 1E circuit breaker, (Ref. 5), takes into consideration the low frequency of operation of the circuit breakers and the low likelihood that operation and maintenance activities at the plant could adversely affect the OPERABILITY of the circuit breaker.

REFERENCES

1.

Watts Bar FSAR, Section 6.0, "Engineered Safety Feature," and Section 15.0, "Accident Analyses."

2.

Not Used.

3.

Watts Bar Wiring Diagram Series 45A710, "Periodic Breaker Test."

4.

NUREG-0847, "Safety Evaluation Report Related to the Operation of Watts Bar Nuclear Plant, Units 1 and 2" including Supplements thereto.

5.

EPRI NP-7410-V3, Molded Case Circuit Breaker Application and Maintenance Guide, Revision 1.

Containment Penetration Conductor Overcurrent Protection Devices B 3.8.2 (continued)

Watts Bar - Unit 2 B 3.8-7 Technical Requirements (developmental)

A B 3.8 ELECTRICAL POWER SYSTEMS B 3.8.2 Containment Penetration Conductor Overcurrent Protection Devices BASES BACKGROUND General Design Criterion (GDC), "Containment Design Basis," of 10 CFR 50, Appendix A requires, in part, that the reactor containment structure be designed so that the containment structure can, without exceeding design leakage rate, accommodate the calculated pressure, temperature, and other environmental conditions resulting from any loss-of-coolant accident. One consideration in meeting the requirements of this GDC is the design of electrical penetrations.

Reference 1 describes a method of complying with GDC Appendix A with respect to the requirements for design, qualification, construction, installation and testing of electric penetration assemblies. It specifies that the electric penetration assembly should be designed to withstand, without loss of mechanical integrity, the maximum short-circuit current vs.

time conditions that could occur given single random failures of circuit overload protection devices.

The function of electrical protective devices is to detect and isolate faults that could occur on the electrical distribution system. These devices therefore provide an effective means of preventing fault currents from challenging the design limit of the penetrations. Containment penetration conductor overcurrent protective devices are installed to further protect the penetration conductors from faults on components inside containment or improper operation of other protective devices in addition to that provided by the distribution system.

APPLICABLE SAFETY ANALYSES The safety design basis for the containment includes the requirement that the containment must withstand the pressures and temperatures of the limiting DBA without exceeding the design leakage rate. The design of the electrical penetrations must therefore provide that they remain intact in the event of faults on components inside containment or penetration conductors that supply these components. The containment penetration conductor overcurrent protective devices provide additional fault protection of the penetrations and help ensure that the design limits of the penetrations are not challenged. However, these overcurrent protective devices are not a structure, system, or component that is part

Containment Penetration Conductor Overcurrent Protection Devices B 3.8.2 BASES (continued)

Watts Bar - Unit 2 B 3.8-8 Technical Requirements (developmental)

A APPLICABLE SAFETY ANALYSES (continued) of the primary success path and which actuates to mitigate a DBA or transient that either assumes a failure of or presents a challenge to the integrity of a fission product barrier (Ref. 2).

TR TR 3.8.2 requires that all containment penetration conductor overcurrent protection devices be OPERABLE. These protection devices are identified on Drawing Series 45A710 (Ref. 3). This assures that the design limits of the containment electrical penetrations will not be challenged as a result of electrical faults on the penetration conductors or the equipment that they supply in containment.

APPLICABILITY The OPERABILITY of the containment penetration conductor overcurrent protection devices is required when the containment is required to be OPERABLE. In MODES 1, 2, 3, and 4, a DBA could cause a release of radioactive material into containment. In MODES 5 and 6, the probability and consequences of these events are reduced because of the pressure and temperature limitations of these MODES. The containment penetration conductor overcurrent protection devices are, therefore, required to be OPERABLE in MODES 1, 2, 3, and 4.

ACTIONS A.1, A.2.1, A.2.2 and A.2.3 With one or more containment penetration conductor overcurrent protection devices inoperable, the circuit(s) associated with the inoperable protection device(s) must be placed in a condition that would preclude the possibility of a fault that could overload the circuit(s). To accomplish this, the circuit is de-energized by either tripping the circuit's backup circuit breaker or by removing the inoperable circuit breaker.

Since systems or components supplied by the affected circuit will no longer have power, they must be declared inoperable.

The 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> Completion Time takes into account the design of the electrical penetration for maximum fault current, the availability of backup circuit protection on the distribution system and the low probability of a DBA occurring during this period. This Completion Time is also considered reasonable to perform the necessary repairs or circuit alterations to restore or otherwise de-energize the affected circuit.

Containment Penetration Conductor Overcurrent Protection Devices B 3.8.2 BASES (continued)

Watts Bar - Unit 2 B 3.8-9 Technical Requirements (developmental)

A ACTIONS A.1, A.2.1, A.2.2 and A.2.3 (continued)

In order to assure that any electrical penetration which is not protected by an overcurrent device remains de-energized, it is necessary to periodically verify that its backup circuit breaker is tripped or that the inoperable circuit breaker is removed. A Completion Time of 7 days is considered sufficient due to the infrequency of plant operations that could result in reenergizing a circuit that has been de-energized in this manner.

B.1 and B.2 If the inoperable containment penetration conductor overcurrent protection devices are not able to be restored to OPERABLE status and the associated circuit cannot be de-energized within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />, the containment penetration is vulnerable to the mechanical effects of a short circuit, should one occur. These effects can challenge the design capability of the penetration and therefore pose a threat to containment integrity. To protect against this possibility, the plant must be placed in a condition where the TR is not applicable. This is done by placing the plant in MODE 3 within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in MODE 5 within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />. The allowed Completion Times are considered reasonable based on operating experience to reach the required plant conditions from full power conditions in an orderly manner and without challenging plant systems.

TECHNICAL SURVEILLANCE REQUIREMENTS As described by Technical Surveillance Requirements general surveillance Note 1, the surveillances for this TR are necessary to assure that the overcurrent protection devices given in Drawing Series 45A710 (excluding fuses) are demonstrated OPERABLE. Note 2 explains that the surveillance requirements apply to at least one Reactor Coolant Pump (RCP) such that all RCP circuits are demonstrated OPERABLE at least once per 72 month period. This recognizes the importance of the RCP circuits to the safe operation of the plant as well as the potentially large amount of short circuit current associated with a fault on these circuits.

Containment Penetration Conductor Overcurrent Protection Devices B 3.8.2 BASES (continued)

Watts Bar - Unit 2 B 3.8-10 Technical Requirements (developmental)

A TECHNICAL SURVEILLANCE REQUIREMENTS (continued)

TSR 3.8.2.1 This surveillance requires the performance of a CHANNEL CALIBRATION of all protective relays associated with medium voltage (6.9 kV) containment penetration overcurrent devices. A CHANNEL CALIBRATION assures that the relays will be able to detect overcurrent conditions on the penetration conductors. The Frequency of 18 months is consistent with the typical industry refueling cycle.

TSR 3.8.2.2 This surveillance requires the performance of an integrated system functional test which verifies that the relays and associated medium voltage (6.9 kV) circuit breakers function as designed to isolate fault currents. An integrated test assures that the individual elements of the protection scheme, the relays, breakers and other control circuits, interact as designed.

The surveillance has been modified by a Note stating that if a failure is discovered in the integrated functional test, an additional representative sample of at least 10% of all the circuit breakers of the inoperable type shall also be tested to assure that there is no common cause failure mechanism that could systematically affect all breakers of a given type.

The Frequency of 18 months coincides with the typical industry refueling cycle.

TSR 3.8.2.3 This surveillance requires the performance of a functional test on a representative sample of 10% of each type of molded-case circuit breaker used as penetration protection. This sample size is sufficiently large to represent the actual failure distribution within the whole population of circuit breakers of a given type used in the plant. If there are any failure mechanisms that could affect the OPERABILITY of the circuit breaker(s) they are likely to have occurred in the sample tested.

The 18 month Frequency takes into consideration the infrequent operation of the breakers and their correspondingly low failure rate. The Surveillance is augmented by three Notes. The first Note states that the breakers shall be selected for testing on a rotating basis. This ensures that all of the breakers will eventually be tested and those failures that may not have been discovered in the initial 10% samples will eventually be discovered.

Containment Penetration Conductor Overcurrent Protection Devices B 3.8.2 BASES (continued)

Watts Bar - Unit 2 B 3.8-11 Technical Requirements (developmental)

A TECHNICAL SURVEILLANCE REQUIREMENTS TSR 3.8.2.3 (continued)

The second Note describes the functional test procedure and the response to be verified to ensure OPERABILITY.

The third Note states that for each molded case circuit breaker found inoperable during functional tests an additional representative sample of 10% of the defective type shall be functionally tested until no more failures are found or all of that type have been functionally tested. This helps to ensure that a failure discovered in the representative sample was not caused by a failure mechanism that could systematically affect other breakers in the overall population of breakers of the same type.

TSR 3.8.2.4 This surveillance requires the performance of a functional test on a representative sample of 10% of each type of electrically-operated circuit breaker used as penetration protection. This sample size is sufficiently large to represent the actual failure distribution within the whole population of circuit breakers of a given type used in the plant. If there are any failure mechanisms that could affect the OPERABILITY of the circuit breaker(s), they are likely to have occurred in the sample tested. The 18 month Frequency takes into consideration the infrequent operation of the breakers and their correspondingly low failure rate.

The Surveillance is augmented by three Notes. The first Note states that the breakers shall be selected for testing on a rotating basis. This ensures that all of the breakers will eventually be tested and those failures that may not have been discovered in the initial 10% samples will eventually be discovered. The second Note describes the functional test procedure and the response to be verified to ensure OPERABILITY.

The third Note states that for each electrically-operated circuit breaker found inoperable during functional tests an additional representative sample of 10% of the defective type shall be functionally tested until no more failures are found or all of that type have been functionally tested.

This helps to ensure that a failure discovered in the representative sample was not caused by a failure mechanism that could systematically affect other breakers in the overall population of breakers of the same type.

Containment Penetration Conductor Overcurrent Protection Devices B 3.8.2 BASES Watts Bar - Unit 2 B 3.8-12 Technical Requirements (developmental)

A TECHNICAL SURVEILLANCE REQUIREMENTS (continued)

TSR 3.8.2.5 This surveillance requires the inspection of each circuit breaker and the performance of preventive maintenance in accordance with procedures prepared in conjunction with the manufacturers recommendation.

Performance of recommended preventive maintenance helps ensure the operability of the circuit breakers. The 72 months periodicity for Class 1E and 96 months for non-Class 1E circuit breakers (Ref. 4) takes into consideration known failure rates for the circuit breakers and operating experience.

REFERENCES

1.

Regulatory Guide 1.63, "Electric Penetration Assemblies in Containment Structures for Nuclear Power Plants," Revision 3.

2.

WCAP-11618, "MERITS Program-Phase II, Task 5, Criteria Application," including Addendum 1 dated April, 1989.

3.

Watts Bar Wiring Diagram Series 45A710, "Periodic Breaker Test."

4.

EPRI NP-7410-V3, Molded Case Circuit Breaker Application and Maintenance Guide, Revision 1.

Motor-Operated Valves Thermal Overload Bypass Devices B 3.8.3 (continued)

Watts Bar - Unit 2 B 3.8-13 Technical Requirements (developmental)

A B 3.8 ELECTRICAL POWER SYSTEMS B 3.8.3 Motor Operated Valves Thermal Overload Bypass Devices BASES BACKGROUND Motor operated valves with thermal overload protection devices for the valve motors are used in safety systems and in their auxiliary supporting systems. Operating experience has shown that indiscriminate application of thermal overload protection devices to these valve motors could result in needless hindrance to successful completion of safety functions (Ref. 1).

Thermal overload relays are designed primarily to protect continuous-duty motors while they are running rather than during starting. Use of these overload devices to protect intermittent-duty motors may therefore result in undesired actuation of the devices if the cumulative effect of heating caused by successive starts at short intervals is not taken into account in determining the overload trip setting.

The accuracy obtainable with the thermal overload relay trip generally varies from -5% to 0% of trip setpoint. Since the primary concern in the application of overload devices is to protect the motor windings against excessive heating, the above negative tolerance in trip characteristics of the protection device is considered in the safe direction for motor protection. However, this conservative design feature built into these overload devices for motor protection could interfere in the successful functioning of a safety related system. An improper thermal overload setting could prevent a vital piece of equipment from performing its intended function.

Reference 1 states that one alternative to "ensure that safety-related motor operated valves whose motors are equipped with thermal overload protection devices will perform their function" is that those thermal overload protection devices that are normally in force during plant operation should be bypassed under accident conditions.

Motor-Operated Valves Thermal Overload Bypass Devices B 3.8.3 BASES (continued)

(continued)

Watts Bar - Unit 2 B 3.8-14 Technical Requirements (developmental)

B APPLICABLE SAFETY ANALYSES The accident analysis (Ref. 2) assumes the availability of the Engineered Safeguards Features to mitigate the consequences of a DBA or transient.

The safety design basis of the containment includes the requirement that the containment must withstand the limiting DBA without exceeding the design leakage rate. Both of these requirements depend upon the actuation of motor-operated valves to perform their safety function.

Thermal overload bypasses minimize the probability that a motor-operated valve will fail to perform its intended safety function due to an unnecessary operation of the thermal overload trip device.

However, these thermal overload protective devices are not a structure, system, or component that is part of the primary success path and which actuates to mitigate a DBA or transient that either assumes a failure of or presents a challenge to the integrity of a fission product barrier (Ref. 3).

TR TR 3.8.3 requires that all thermal overload bypass devices shall be OPERABLE. The OPERABILITY of the motor-operated valves thermal overload bypass devices ensures that thermal overload devices will not prevent safety-related valves from performing their function.

APPLICABILITY The OPERABILITY of the motor-operated valves thermal overload bypass devices ensures that these devices will not prevent safety-related valves from performing their function. They therefore help ensure the OPERABILITY of these motor-operated valves and are required to be operable whenever the valves that they are designed to ensure operable are required to be OPERABLE.

Motor-Operated Valves Thermal Overload Bypass Devices B 3.8.3 BASES (continued)

Watts Bar - Unit 2 B 3.8-15 Technical Requirements (developmental)

A ACTIONS A.1 and A.2 With thermal overload protection not bypassed when required for one or more of the valves listed in Table 3.8.3-1, the actuation of the thermal overload trip device could open or remove power from a motor before the safety function has been completed or even started. Providing an alternate means to bypass the thermal overload would effectively prevent the removal of power from a motor by the thermal overload device. An 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> Completion Time takes into consideration the low probability of these motor-operated valves being required to operate during this period, and is considered to be a reasonable amount of time to either restore the bypass device to OPERABLE status or provide an alternative means of bypassing the thermal overload device.

B.1 and B.2 If the Required Actions and associated Completion Times of Condition A cannot be met, then motor-operated valves with inoperable thermal overload bypass devices cannot be considered OPERABLE. Declaring these valves inoperable and applying the appropriate ACTION statement(s) of the affected systems ensures the inoperability of a bypass device will not result in unacceptable deviations from any TRs or LCOs applicable to their associated valves.

TECHNICAL SURVEILLANCE REQUIREMENTS TSR 3.8.3.1 This surveillance requires that a TADOT be performed every 18 months.

This ensures continued functional reliability and accuracy of the trip point.

The 18 month Frequency is based upon the known reliability of the thermal overload bypass device and has been shown to be acceptable through operating experience.

REFERENCES

1.

Regulatory Guide 1.63, Electric Penetration Assemblies in Containment Structures for Nuclear Power Plants," Revision 3.

2.

Watts Bar FSAR, Section 15, "Accident Analysis."

3.

WCAP-11618, "MERITS Program-Phase II, Task 5, Criteria Application," including Addendum 1 dated April, 1989.

Submerged Component Circuit Protection B 3.8.4 (continued)

Watts Bar - Unit 2 B 3.8-16 Technical Requirements (developmental)

A B 3.8 ELECTRICAL POWER SYSTEMS B 3.8.4 Submerged Component Circuit Protection BASES BACKGROUND Electrical equipment located inside containment has been designed to maintain equipment safety functions and to prevent unacceptable spurious actuations. All power cables feeding equipment inside containment are provided with individual breakers to protect the power sources (both Class 1E and non-Class 1E) from the effects of electrical shorts. Reactor coolant pumps have two circuit breakers. All other power cables are provided with a cable protector fuse which, in the event of a breaker failure, is designed to protect the containment penetration.

These breakers and protector fuses ensure that, should an electrical short occur inside containment, the electrical power source will not be affected.

A failure analysis has been made on the ability of the electrical power (both AC and DC) systems to withstand failure of submerged electrical components from the postulated LOCA flood levels inside containment (Ref. 1 and 5). Some of the identified components are automatically de-energized in event of a LOCA. The remaining components that are powered from a Class 1E source were assumed to have a high impedance fault for the analysis. The magnitude of the leakage currents used in the analysis is the maximum value of current that each protective device would carry for an indefinite period (i.e., the protective device's thermal rating). The results of the evaluations indicate that the submergence of electrical components will not prevent the Class 1E electric (either AC or DC) systems from performing their intended safety function for the postulated submerged condition.

A listing of major electrical components located inside containment that may be inundated following a LOCA is found in Reference 2 along with an explanation of the safety significance of the failure of the equipment due to flooding. These components are automatically de-energized by the accident signal and the accident signal must be reset to remove the automatic trip signal from each component.

Submerged Component Circuit Protection B 3.8.4 BASES (continued)

(continued)

Watts Bar - Unit 2 B 3.8-17 Technical Requirements (developmental)

B APPLICABLE SAFETY ANALYSES The Accident Analysis (Ref. 3) assumes the availability of the Engineered Safeguards Features to mitigate the consequences of a DBA or transient.

The safety design basis of the containment includes the requirement that the containment must withstand the limiting DBA without exceeding the design leakage rate. Both of these requirements depend upon the actuation of motors and valves to perform their safety function. An electrical or mechanical failure on a submerged component has the potential to interfere with the ability of some other safety component or system to perform its intended function. By de-energizing their associated component on accident conditions, submerged component circuits minimize the potential for this type of interference with safety functions. They are not, however, systems or components that are part of the primary success path and which actuate to mitigate a DBA or transient that either assumes a failure of or presents a challenge to the integrity of a fission product barrier (Ref. 4).

TR TR 3.8.4 requires that all submerged component circuits associated with valves 2-FCV-74-1, 2-FCV-74-2, 2-FCV-74-8, and 2-FCV-74-9 shall be de-energized and with each component listed in Table 3.8.4-1 shall be OPERABLE. The OPERABILITY of the submerged component circuits ensures that electrical or mechanical faults on submerged components will not interfere with the ability of other safety related equipment, or the Class 1E distribution, to perform its safety function.

APPLICABILITY Electrical or mechanical faults on valves 2-FCV-74-1, 2-FCV-74-2, 2-FCV-74-8, and 2-FCV-74-9, and the components listed in Table 3.8.4-1 could potentially affect systems or components necessary to mitigate the consequences of DBAs or transients that could occur in MODES 1, 2, 3, or 4. The submerged component circuits are therefore required to be OPERABLE during these MODES in order to de-energize potentially submerged components.

Submerged Component Circuit Protection B 3.8.4 BASES (continued)

(continued)

Watts Bar - Unit 2 B 3.8-18 Technical Requirements (developmental)

B ACTIONS A.1 With the circuits for valves 2-FCV-74-1, 2-FCV-74-2, 2-FCV-74-8 and 2-FCV-74-9 energized with RCS pressure > 425 psig or with one or more submerged components circuits (Table 3.8.4-1) inoperable, the associated submerged components could remain energized in the event of an accident. In order to prevent the adverse effects of a potential fault on an energized submerged component during an accident, it is necessary to restore the ability to automatically de-energize the component under accident conditions or to maintain a de-energized configuration for components not required to be functional. This can be done by restoring the inoperable circuit to OPERABLE status. The Completion Time of 7 days takes into consideration the low probability of an accident occurring which would cause the components to be submerged. It is a reasonable amount of time to complete the work necessary to restore the circuits to OPERABLE status.

B.1 and B.2 If the submerged component circuits cannot be restored to OPERABLE status within the 7 day Completion Time, it is necessary to place the plant in a Condition where the function of the circuits is not needed. This can be accomplished by first placing the plant in MODE 3 and then in MODE 5. The Completion Time of 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> to reach MODE 3 and 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> to reach MODE 5 are considered to be reasonable times for placing the plant into a condition where the TR is not applicable in a controlled manner.

TECHNICAL SURVEILLANCE REQUIREMENTS TSR 3.8.4.1 This surveillance requires verification that valves 2-FCV-74-1, 2-FCV-74-2, 2-FCV-74-8, and 2-FCV-74-9 are de-energized by removal of power at the 480V motor control centers. These valves are required to be shut in MODES 1, 2, 3, and 4, and are interlocked so that they cannot be opened until RCS Pressure is reduced to < 425 psig. The Frequency of 31 days is considered reasonable based on plant operating experience.

Submerged Component Circuit Protection B 3.8.4 BASES Watts Bar - Unit 2 B 3.8-19 Technical Requirements (developmental)

B TECHNICAL SURVEILLANCE REQUIREMENTS (continued)

TSR 3.8.4.2 This surveillance requires verification that the components shown in Table 3.8.4-1 are automatically de-energized on a simulated accident signal. Since the function of OPERABLE submerged component circuits for the valves shown in the Table is to de-energize the components under accident conditions, verification that the valves are, in fact, de-energized on a simulated accident signal also constitutes verification that the submerged component circuits are OPERABLE. The 18 month Frequency corresponds to the availability of the components for testing during plant refueling.

REFERENCES

1.

Watts Bar FSAR, Section 8.3.1.2.3, "Safety-Related Equipment in a LOCA Environment."

2.

Watts Bar FSAR, Table 8.3-28, "Major Electrical Equipment That Could Become Submerged Following a LOCA."

3.

Watts Bar FSAR, Section 15.0, "Accident Analyses."

4.

WCAP-13470, "Watts Bar Unit 1 Technical Specifications Criteria Application Report," dated August, 1992.

5.

Watts Bar Electrical Calculation EDQ00299920080020.