CNL-20-016, Application to Modify Watts Bar Nuclear Plant Unit 1 Technical Specifications 3.3.3, Post Accident Monitoring Instrumentation, (WBN-TS-19-23)

Application to Modify Watts Bar Nuclear Plant Unit 1 Technical Specifications 3.3.3, Post Accident Monitoring Instrumentation, (WBN-TS-19-23)

ML20174A546
Person / Time
Site:	Watts Bar
Issue date:	06/22/2020
From:	Jim Barstow Tennessee Valley Authority
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
CNL-20-016
Download: ML20174A546 (17)

Text

Tennessee Valley Authority, 1101 Market Street, Chattanooga, Tennessee 37402 CNL-20-016 June 22, 2020 10 CFR 50.90 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555-0001 Watts Bar Nuclear Plant, Unit 1 Facility Operating License No. NPF-90 NRC Docket No. 50-390

Subject:

Application to Modify Watts Bar Nuclear Plant Unit 1 Technical Specifications 3.3.3, Post Accident Monitoring Instrumentation,"

(WBN-TS-19-23)

In accordance with the provisions of Title 10 of the Code of Federal Regulations (10 CFR) 50.90, Application for amendment of license, construction permit, or early site permit, Tennessee Valley Authority (TVA) is submitting a request for an amendment to Technical Specifications (TS) for the Watts Bar Nuclear Plant (WBN) Unit 1.

The proposed license amendment request (LAR) revises WBN Unit 1 TS 3.3.3, Post Accident Monitoring (PAM) Instrumentation," Table 3.3.3-1, to delete the term plasma from the footnotes in the PAM instrumentation table. The proposed changes will allow future modifications to upgrade the Inadequate Core Cooling Monitor (ICCM) PAM display, while still meeting the requirements of the PAM instrumentation functions.

The enclosure to this submittal provides a description and technical evaluation of the proposed change, a regulatory evaluation, and a discussion of environmental considerations. to the enclosure provides the existing WBN Unit 1 TS page marked-up to show the proposed changes. Attachment 2 to the enclosure provides the existing WBN Unit 1 TS page retyped to show the proposed change. Attachment 3 to the enclosure provides the existing WBN Unit 1 TS Bases pages marked-up to show the proposed changes. Changes to the existing TS Bases are provided for information only and will be implemented under the TS Bases Control Program.

TVA has determined that there are no significant hazard considerations associated with the proposed change and that the change qualifies for a categorical exclusion from environmental review pursuant to the provisions of 10 CFR 51.22(c)(9). In accordance with 10 CFR 50.91, Notice for Public Comment; State Consultation, TVA is sending a copy of this letter and the enclosure to the Tennessee Department of Environment and Conservation.

U.S. Nuclear Regulatory Commission CNL-20-016 Page 2 June 22, 2020 TVA requests approval of the proposed license amendment within one year from the date of this submittal with implementation within 30 days following NRC approval.

There are no new regulatory commitments associated with this submittal. If you have any questions regarding this information, please contact Gordon Williams, Senior Manager, Fleet Licensing (Acting) at (423) 751-2687.

I declare under penalty of perjury that the foregoing is true and correct. Executed on this 22nd day of June 2020.

Respectfully, James Barstow Vice President, Nuclear Regulatory Affairs & Support Services

Enclosure:

Evaluation of Proposed Change cc (Enclosure):

NRC Regional Administrator - Region II NRC Project Manager - Watts Bar Nuclear Plant NRC Senior Resident Inspector - Watts Bar Nuclear Plant Director, Division of Radiological Health - Tennessee State Department of Environment and Conservation

Evaluation of Proposed Change

Subject:

Application to Modify Watts Bar Nuclear Plant Unit 1 Technical Specifications 3.3.3, Post Accident Monitoring Instrumentation,"

(WBN-TS-19-23)

CONTENTS 1.0

SUMMARY

DESCRIPTION ............................................................................................. 2 2.0 DETAILED DESCRIPTION.............................................................................................. 2 2.1 Proposed Changes ...................................................................................................... 2 2.2 Reason for the Proposed Changes .............................................................................. 2

3.0 TECHNICAL EVALUATION

............................................................................................. 3 3.1 System Description ...................................................................................................... 3 3.2 Technical Analysis ....................................................................................................... 3 3.2.1 WBN Unit 1 PAM Display ...................................................................................... 4 3.2.2 Conclusion ............................................................................................................ 4

4.0 REGULATORY EVALUATION

........................................................................................ 4 4.1 Applicable Regulatory Requirements and Criteria ........................................................ 4 4.2 Precedent .................................................................................................................... 5 4.3 Significant Hazards Consideration ............................................................................... 5 4.4 Conclusion ................................................................................................................... 7

5.0 ENVIRONMENTAL CONSIDERATION

........................................................................... 7

6.0 REFERENCES

................................................................................................................ 7 ATTACHMENTS

1. Proposed TS Changes (Mark-Ups) for WBN Unit 1

2. Proposed TS Changes (Final Typed) for WBN Unit 1

3. Proposed TS Bases Page Changes (Mark-Ups) for WBN Unit 1 (For Information Only)

CNL-20-010 E1 of 7

1.0

SUMMARY

DESCRIPTION In accordance with the provisions of Title 10 of the Code of Federal Regulations (10 CFR) 50.90, "Application for amendment of license, construction permit, or early site permit," Tennessee Valley Authority (TVA) is requesting a license amendment to Facility Operating License No. NPF-90 for the Watts Bar Nuclear Plant (WBN) Unit 1.

The proposed license amendment request (LAR) revises WBN Unit 1 Technical Specifications (TS) 3.3.3, Post Accident Monitoring (PAM) Instrumentation," Table 3.3.3-1, to delete the term plasma from the footnotes in the PAM instrumentation table.

The proposed changes will allow future modifications to upgrade the Inadequate Core Cooling Monitor (ICCM) PAM display, while still meeting the requirements of the PAM instrumentation functions.

2.0 DETAILED DESCRIPTION

2.1 PROPOSED CHANGE

S The following is a detailed description of the proposed WBN Unit 1 TS changes.

• Table 3.3.3-1 (page 2 of 2) in TS 3.3.3 is revised as follows:

(f) The ICCM provides these functions on a plasma display.

(h) This function is displayed on the ICCM plasma display and digital panel meters.

Attachment 1 to the enclosure provides the existing WBN Unit 1 TS page marked-up to show the proposed changes. Attachment 2 to the enclosure provides the existing WBN Unit 1 TS page retyped to show the proposed changes. Attachment 3 to the enclosure provides the existing WBN Unit 1 TS Bases pages marked-up to show the proposed changes. Changes to the existing TS Bases are provided for information only and will be implemented under the TS Bases Control Program.

2.2 REASON FOR THE PROPOSED CHANGES The word plasma in the term plasma display sets an unnecessary restraint on the technology used for providing the ICCM display in the WBN Unit 1 PAM system, which limits the use of components with features superior to the original plasma display units.

CNL-20-016 E2 of 7

3.0 TECHNICAL EVALUATION

3.1 SYSTEM DESCRIPTION The PAM instrumentation for WBN Unit 1 is required to monitor plant and environs conditions during and following design basis Condition II, III and IV faults as described in the WBN dual-unit Updated Final Safety Analysis Report (UFSAR) Chapter 15. PAM instrumentation enables the Main Control Room (MCR) operating staff to take preplanned manual actions, provide information on whether critical safety functions are being accomplished, provide information for potential or actual breach of the barriers to fission product release, provide information of individual safety systems, and provide information on the magnitude of the release of radioactive materials.

Parameters are displayed on individual devices located in the MCR or processed for display by one of the computer-based systems available in the MCR, with the exceptions that some parameters are displayed on local panels if specific guidelines set forth in UFSAR Chapter 7 are met, and that portable or post accident sampling devices are not displayed in the MCR.

The PAM System (PAMS) is a computer-based system that displays three post accident parameters:

• Core exit thermocouples - Two independent channels (PAM 1 and PAM 2) for monitoring core exit temperature are provided. The core exit thermocouples were added to the plant design to provide direct indication of degrading core cooling conditions following transient events similar to that experienced at Three Mile Island (TMI).

• Reactor vessel level - This is the compensated actual vessel level derived from a microprocessor algorithm using the upper range, lower range, dynamic range differential pressure, wide range temperature, and wide range pressure.

• Subcooled margin monitor - The PAMS software uses inputs from plant instrumentation and core exit thermocouples to calculate subcooled margin.

The three parameters displayed by PAMS are key variables as defined by Regulatory Guide 1.97 (RG 1.97) Instrumentation for Light-Water Cooled Nuclear Power Plants to Assess Plant and Environs Conditions During and Following an Accident (Reference 1).

3.2 TECHNICAL ANALYSIS

The requirements for instrumentation used to assess plant and environs conditions during and following an accident at WBN are based on satisfying the intent of RG 1.97, as mandated by TVA commitments to comply with NUREG-0737 Supplement 1 (Reference 2).

RG 1.97 requires that key variables must be displayed in a manner that allows the control room operators to take the appropriate manual actions. Review of applicable human factor standards for visual display units indicates no regulatory requirements calling for a specific display technology.

CNL-20-016 E3 of 7

3.2.1 WBN Unit 1 PAM Display The PAM display panel in use at WBN Unit 1 from original licensing to the present time is a plasma display. Plasma display technology was invented in 1964 as an alternative to the cathode ray tube (CRT) then in use for television sets. The plasma display was one of the first flat panel displays and was considered superior to the existing CRT technology. The WBN Unit 1 plasma display was manufactured by a company known as Electro-Plasma, Inc.

RG 1.97 makes no mention of what technology should be used to display parameters in the MCR.

The PAM display panel does not perform any calculations or any critical/essential function of the PAMS other than as a visual display. The display is used as indication only. Based on review of References 3 and 4, it is surmised that the word plasma was included in the term plasma display for WBN Unit 1 TS 3.3.3 to highlight that the latest in display technology was being used. However, this situation constitutes a technical specification requirement to retain an outmoded technology.

3.2.2 Conclusion The current wording of the footnotes for Table 3.3.3-1 in TS 3.3.3 for WBN Unit 1 was developed in an effort to be informative and descriptive in support of the initial licensing process. In hindsight, it is recognized that an extraneous term was included that needlessly limits the ability to perform modifications to the PAM display that otherwise meet the requirements of the associated functions.

TVA considers the proposed TS change to remove the word plasma from the footnotes in the PAM instrumentation table to be an effective approach for maintaining the most efficient technology in this area, providing better access to spare parts and service support. This promotes the availability of these RG 1.97 parameter displays.

4.0 REGULATORY EVALUATION

4.1 APPLICABLE REGULATORY REQUIREMENTS AND CRITERIA 10 CFR 50.90, Application for Amendment of License, Construction Permit, or Early Site Permit, requires that whenever a holder of a license desires to amend the license or permit, application for an amendment must be filed with the Commission.

10 CFR 50 Appendix A, General Design Criterion (GDC) 13, Instrumentation and Control, requires that instrumentation shall be provided to monitor variables and systems over their anticipated ranges for normal operation, for anticipated operational occurrences, and for accident conditions as appropriate to assure adequate safety, including those variables and systems that can affect the fission process, the integrity of the reactor core, the reactor coolant pressure boundary, and the containment and its associated systems. Appropriate controls shall be provided to maintain these variables and systems within prescribed operating ranges. Compliance with GDC 13 is described in Section 3.1.2.2 of the WBN UFSAR.

CNL-20-016 E4 of 7

GDC 19, Control Room, requires that a control room shall be provided from which actions can be taken to operate the nuclear power unit safely under normal conditions and to maintain it in a safe condition under accident conditions, including loss-of-coolant accidents. Adequate radiation protection shall be provided to permit access and occupancy of the control room under accident conditions without personnel receiving radiation exposures in excess of five rem whole body, or its equivalent to any part of the body, for the duration of the accident. Equipment at appropriate locations outside the control room shall be provided (1) with a design capability for prompt hot shutdown of the reactor, including necessary instrumentation and controls to maintain the unit in a safe condition during hot shutdown, and (2) with a potential capability for subsequent cold shutdown of the reactor through the use of suitable procedures. Compliance with GDC 19 is described in Section 3.1.2.2 of the WBN UFSAR.

Conclusion The design standards for the PAM instrumentation ensure the availability of required monitoring instrumentation in the control room during a post accident scenario. The proposed TS changes do not affect the ability of the PAM instrumentation to perform its intended function.

4.2 PRECEDENT While there is no exact precedent for this LAR, precedence does exist in the TS for other nuclear plants. The PAM Instrumentation tables in the TS for the following nuclear plants, as well as the Standard Technical Specifications for Westinghouse Pressurized Water Reactors, were reviewed with no mention of the PAM display technology found:

• Calvert Cliffs Units 1 and 2

• Catawba Units 1 and 2

• DC Cook Units 1 and 2

• McGuire Units 1 and 2

• Sequoyah Unit 1 and 2

• St. Lucie Units 1 and 2

• Turkey Point Units 3 and 4

• Waterford Unit 3 4.3 SIGNIFICANT HAZARDS CONSIDERATION Tennessee Valley Authority (TVA) proposes to revise the Watts Bar Nuclear Plant Unit 1 Technical Specifications 3.3.3, Post Accident Monitoring (PAM) Instrumentation," to delete the term plasma from the footnotes in the PAM instrumentation table. This will provide a more effective approach for maintaining the most efficient technology in this area, providing better access to spare parts and service support. This then promotes the availability of these Regulatory Guide 1.97 parameter displays.

CNL-20-016 E5 of 7

TVA has evaluated whether or not a significant hazards consideration is involved with the proposed amendment(s) by focusing on the three standards set forth in 10 CFR 50.92, Issuance of amendment, as discussed below:

1. Does the proposed amendment involve a significant increase in the probability or consequence of an accident previously evaluated?

Response: No The proposed changes do not require physical changes to plant systems, structures, or components. There is no interaction with a potential accident-initiating mechanism. The design standards for the PAM instrumentation addressed in these TS tables ensure the availability of required monitoring instrumentation in the control room during a post accident scenario.

Therefore, the proposed changes do not involve a significant increase in the probability or consequences of an accident previously evaluated.

2. Does the proposed amendment create the possibility of a new or different kind of accident from any accident previously evaluated?

Response: No.

The proposed changes do not introduce new or different accidents to be postulated and subsequently evaluated, and no changes are being made to the plant that would introduce any new accident causal mechanisms. This license amendment request does not affect any plant systems that are potential accident initiators; nor does it have any significantly adverse effect on any accident mitigating systems.

The proposed change does not change the functional requirements, configuration, or method of operation of any system or component. Under the proposed change, no additional plant equipment will be installed.

Therefore, the proposed changes do not create the possibility of a new or different kind of accident from any previously evaluated.

3. Does the proposed amendment involve a significant reduction in a margin of safety?

Response: No.

The proposed changes do not alter the permanent plant design, nor does it change the assumptions contained in the safety analyses. No safety limits or operating parameters used to establish the safety margin are affected. The safety margins included in analyses of accidents are not affected by the proposed change.

Therefore, the proposed changes do not involve a significant reduction in a margin of safety.

CNL-20-016 E6 of 7

Based on the above, TVA concludes that the proposed amendment does not involve a significant hazards consideration under the standards set forth in 10 CFR 50.92(c), and accordingly, a finding of no significant hazards consideration is justified.

4.4 CONCLUSION

In conclusion, based on the considerations discussed above, (1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Commissions regulations, and (3) the issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public.

5.0 ENVIRONMENTAL CONSIDERATION

A review has determined that the proposed amendment would change a requirement with respect to installation or use of a facility component located within the restricted area, as defined in 10 CFR 20, or would change an inspection or surveillance requirement. However, the proposed amendment does not involve (i) a significant hazards consideration, (ii) a significant change in the types or significant increase in the amounts of any effluents that may be released offsite, or (iii) a significant increase in individual or cumulative occupational radiation exposure. Accordingly, the proposed amendment meets the eligibility criterion for categorical exclusion set forth in 10 CFR 51.22(c)(9). Therefore, pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the proposed amendment.

6.0 REFERENCES

1. Regulatory Guide (RG) 1.97, Instrumentation for Light-Water Cooled Nuclear Power Plants to Assess Plant and Environs Conditions During and Following an Accident, Revision 2, dated December 1980 (ML060750525)

2. NUREG-0737 Supplement 1, Clarification of TMI Action Plan Requirements, dated January 1983 (ML102560009)

3. TVA Letter to NRC, Watts Bar Nuclear Plant (WBN) Units 1 and 2 - NUREG-0737, Item II.F.2 - Instrumentation for Detection of Inadequate Core Cooling (ICC) -

Proposed License Condition 3 (TAC Numbers M77132 and M77133), dated January 24, 1992 (ML073550370)

4. NUREG-0847 Supplement 10, Safety Evaluation Report Related to the Operation of Watts Bar Nuclear Plant Units 1 and 2, dated October 1992 (ML072060473)

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Attachment 1 Proposed TS Changes (Mark-Ups) for WBN Unit 1 CNL-20-016

PAM Instrumentation 3.3.3 Table 3.3.3-1 (page 2 of 2)

Post Accident Monitoring Instrumentation APPLICABLE MODES CONDITION OR OTHER REFERENCED FROM SPECIFIED REQUIRED REQUIRED FUNCTION CONDITIONS CHANNELS/TRAINS ACTION D.1

18. Core Exit Temperature- 1,2,3 2 (e) E Quadrant 2(f)

19. Core Exit Temperature- 1,2,3 2 (e) E (f)

Quadrant 3 (e)

20. Core Exit Temperature- 1,2,3 2 E (f)

Quadrant 4

21. Auxiliary Feedwater Flow 1,2,3 2/SG E

22. Reactor Coolant System 1,2,3 2 E (h)

Subcooling Margin Monitor

23. Refueling Water Storage Tank 1,2,3 2 E Water Level

24. Steam Generator Pressure 1,2,3 2/SG E

25. Auxiliary Building Passive Sump 1,2,3 2 E (j)

Level (a) Below the P-10 (Power Range Neutron Flux) interlocks.

(b) Above the P-6 (Intermediate Range Neutron Flux) interlocks.

(c) Below the P-6 (Intermediate Range Neutron Flux) interlocks.

(d) Not required for isolation valves whose associated penetration is isolated by at least one closed and deactivated automatic valve, closed manual valve, blind flange, pressure relief valve, or check valve with flow through the valve secured.

(e) A channel consists of two core exit thermocouples (CETs).

(f) The ICCM provides these functions on a plasma display.

(g) Regulatory Guide 1.97, non-Type A, Category 1 Variables.

(h) This function is displayed on the ICCM plasma display and digital panel meters.

(i) Only one position indication channel is required for penetration flow paths with only one installed control room indication channel.

(j) Watts Bar specific (not required by Regulatory Guide 1.97) non-Type A Category 1 variable.

Watts Bar-Unit 1 3.3-45 Amendment 72, 132, XX

Enclosure Attachment 2 Proposed TS Changes (Final Typed) for WBN Unit 1 CNL-20-016

PAM Instrumentation 3.3.3 Table 3.3.3-1 (page 2 of 2)

Post Accident Monitoring Instrumentation APPLICABLE MODES CONDITION OR OTHER REFERENCED FROM SPECIFIED REQUIRED REQUIRED FUNCTION CONDITIONS CHANNELS/TRAINS ACTION D.1

18. Core Exit Temperature- 1,2,3 2 (e) E Quadrant 2(f)

19. Core Exit Temperature- 1,2,3 2 (e) E (f)

Quadrant 3 (e)

20. Core Exit Temperature- 1,2,3 2 E (f)

Quadrant 4

21. Auxiliary Feedwater Flow 1,2,3 2/SG E

22. Reactor Coolant System 1,2,3 2 E (h)

Subcooling Margin Monitor

23. Refueling Water Storage Tank 1,2,3 2 E Water Level

24. Steam Generator Pressure 1,2,3 2/SG E

25. Auxiliary Building Passive Sump 1,2,3 2 E (j)

Level (a) Below the P-10 (Power Range Neutron Flux) interlocks.

(b) Above the P-6 (Intermediate Range Neutron Flux) interlocks.

(c) Below the P-6 (Intermediate Range Neutron Flux) interlocks.

(d) Not required for isolation valves whose associated penetration is isolated by at least one closed and deactivated automatic valve, closed manual valve, blind flange, pressure relief valve, or check valve with flow through the valve secured.

(e) A channel consists of two core exit thermocouples (CETs).

(f) The ICCM provides these functions on a display.

(g) Regulatory Guide 1.97, non-Type A, Category 1 Variables.

(h) This function is displayed on the ICCM display and digital panel meters.

(i) Only one position indication channel is required for penetration flow paths with only one installed control room indication channel.

(j) Watts Bar specific (not required by Regulatory Guide 1.97) non-Type A Category 1 variable.

Watts Bar-Unit 1 3.3-45 Amendment 72, 132, XX

Enclosure Attachment 3 Proposed TS Bases Changes (Mark-Ups) for WBN Unit 1 (For Information Only)

CNL-20-016

PAM Instrumentation B 3.3.3 BASES LCO 6. Reactor Vessel Water Level (continued)

Reactor Vessel Water Level, a non-Type A, Category 1 variable, is provided for verification and long term surveillance of core cooling. It is also used for accident diagnosis and to determine reactor coolant inventory adequacy.

The Reactor Vessel Level Instrumentation System (RVLIS) provides a direct measurement of the liquid level above the bottom of the reactor vessel up to the top of the reactor vessel. Indication is in percent of this distance (i.e., the reactor vessel bottom is 0% and the vessel top is 100%). It also has a dynamic range vessel liquid content (% LIQ) normalized from 20% to 100%. Normalization corrects the transmitted level information for the RCP operational configuration so that the accurate dynamic % LIQ is indicated regardless of the pattern of pumps running or the fluid density. Control room indications are provided through the ICCM plasma display. The ICCM plasma display is the primary indication used by the operator during an accident.

7. Containment Sump Water Level (Wide Range)

Containment Sump Water Level is provided for event identification, and verification and long term surveillance of RCS integrity.

Containment Sump Water Level is used to:

Verify water source for recirculation mode of ECCS operation after a LOCA.

Determine whether high energy line rupture has occurred inside or outside containment.

8. Containment Lower Compartment Atmospheric Temperature The lower compartment temperature monitors will verify the temperatures in the lower compartment after an accident with display in the main control room. The monitoring system consists of two channels with range 0F to 350F.

(continued)

Watts Bar-Unit 1 B 3.3-108 Amendment XX

PAM Instrumentation B 3.3.3 BASES LCO 14, 15. Steam Generator Water Level (Wide and Narrow Range)

(continued)

Narrow range steam generator level is used to make a determination on the nature of the accident in progress, e.g., verify a steam generator tube rupture. Steam generator level (Narrow Range) is also used to help identify the ruptured steam generator following a tube rupture and verify that the intact steam generators are an adequate heat sink for the reactor. Narrow range steam generator water level is used when verifying plant conditions for termination of SI during secondary plant high energy line breaks outside containment.

16. AFW Valve Status The status of each AFW swap over to Essential Raw Cooling Water (ERCW) valve is monitored with non-Type A Category 1 indication in the control room. Indication on each valve for fully open or fully closed position is provided. AFW valve status is monitored to give verification to the operator that automatic transfer to ERCW has taken place.

17, 18, 19, 20. Core Exit Temperature Core Exit Temperature is provided for verification and long term surveillance of core cooling.

Core exit thermocouples, in conjunction with RCS wide range temperatures, are sufficient to provide indication of radial distribution of the coolant enthalpy rise across representative sections of the core.

Core Exit Temperature is used to support determination of whether to terminate SI, if still in progress, or to reinitiate SI if it has been stopped.

Core Exit Temperature is also used for unit stabilization and cooldown control.

The Inadequate Core Cooling Monitor (ICCM) is used to monitor the core exit thermocouples. There are two isolated systems, with each system monitoring at least four thermocouples per quadrant. The plasma display gives the average quadrant value, the high quadrant value, and the low quadrant value for each quadrant.

Two OPERABLE channels are required in each quadrant to provide adequate indication of coolant temperature rise in representative regions of the core. Two isolated channels of two thermocouples each ensure a single failure will not disable the ability to identify significant temperature gradients.

The incore thermocouple monitoring system described in Reference 4 (continued)

Watts Bar-Unit 1 B 3.3-111 Revision 135 Amendment XX

PAM Instrumentation B 3.3.3 BASES supports the plant operating procedures.

LCO 21. Auxiliary Feedwater Flow (continued)

AFW Flow is provided to monitor operation of decay heat removal via the SGs.

Redundant monitoring capability is provided by two independent trains of instrumentation for each SG. Each differential pressure transmitter provides an input to a control room indicator. Since the primary indication used by the operator during an accident is the control room indicator, the PAM specification deals specifically with this portion of the instrument channel.

AFW flow is used three ways:

to verify AFW flow to the SGs; to determine whether to terminate SI if still in progress, in conjunction with SG water level (narrow range); and to regulate AFW flow so that the SG tubes remain covered.

22. Reactor Coolant System Subcooling Margin Monitor The RCS subcooling margin monitor is used to determine the temperature margin to saturation of the primary coolant. Control room indications are provided through the ICCM plasma display and digital panel meters. The ICCM plasma display is the primary indication used by the operator during an accident.

23. Refueling Water Storage Tank Level RWST water level is used to verify the water source availability to the ECCS and Containment Spray (CS) Systems. It alerts the operator to manually switch the CS suction from the RWST to the containment sump. It may also provide an indication of time for initiating cold leg recirculation from the sump following a LOCA.

24. Steam Generator Pressure Steam pressure is used to determine if a high energy secondary line rupture has occurred and the availability of the steam generators as a heat sink. It is also used to verify that a faulted steam generator is isolated. Steam pressure may be used to ensure proper cooldown rates or to provide a diverse indication for natural circulation cooldown.

(continued)

Watts Bar-Unit 1 B 3.3-112 Revision 135 Amendment XX