ML20207E419

Safety Evaluation Supporting Compliance W/Atws Rule 10CFR50.62, Requirements for Reduction of Risk from ATWS Events for Light Water Cooled Nuclear Power Plants

ML20207E419
Person / Time
Site:	Point Beach
Issue date:	08/04/1988
From:	Office of Nuclear Reactor Regulation
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Shared Package
ML20207E410	List: ML20207E406 ML20207E419
References
NUDOCS 8808180041
Download: ML20207E419 (9)

Text

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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION WISCONSIN ELECTRIC POWER COMPANY POINT BEACH NUCLEAR PLANT, UNIT N05. 1 AND 2 DOCKET N05. 50-266 AND 50-301 COMPLIANCE WITH ATWS RULE 10 CFR 50.62

1.0 INTRODUCTION

On July 26,1984. Title 10 of the Coce of Federal Regulations (CFR) was amended to include Section 10 CFR 50.62, "Requirements for Reduction of Risk from Anticipated Transients Without Scram (ATWS) Events for Light-Water-Cooled Nuclear Power Plants" (known as the ATWS Rule). The requirements of Section 10 CFR 50.62 apply to all commercial light-water-cooled nucle.ar power plants.

An ATWS is an anticipated operational occurrence (such as loss of feedwater, loss of condenser vacuum, or loss of offsite power) that is accompanied by a failure of the Reactor Trip System (RTS) to shut down the redctor. The ATWS Rule requires specific improvements in the design and operation of commercit.1 nuclear power facilities to reduce the probability of failure to shut down the reactor following enticipated transients and to mitigate the consequences of an ATWS event.

3 ragraph (c)(1) of 10 CFR 50.62 specifies the basic ATWS mitigation system requirements for Westinghouse plants.

Equipment, diverse from the RTS, is required to initiate the auxiliary feedwater (AFW) system and a turbine trip for ATWS events.

In response to paragraph (c)(1), the Westinghouse Owners Group (WOG) developed a set of conceptual ATWS mitigating system actuation circuitry (AMSAC) designs generic to Westinghouse plants. WOG issued Westing-house Topical Report WCAP-10858, "AMSAC Generic Design Package," which provided Information on the various Westinghouse designs.

The staff reviewed WCAP-10858 and issued a safety evaluation of the subject topical report on July 7,1986 (Ref.1).

In this safety evaluation, the staff concluded that the generic designs presented in WCAP-10858 adequately meet the requirements of 10 CFR 50.62. The approved version of the WCAP is labeled WCAP-10858-P-A.

During the course of the staff's review of the proposed AMSAC design,'the WOG issued Addendum 1 to WCAP-10858-P-A by letter dated February 26,1987(Ref.2).

This Addendum changed the setpoint of the C-20 AMSAC permissive signal from 70%

reactor power to 40% power. On August 3, 1987, the WOG issued Revision 1 to WCAP-10858-P-A(Ref.3),whichincorporatedAddendum1changesandprovided 8808180041 880804 PDR ADOCK 05000266 P

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i details on the variable timer and the C-20 time delay.

For those plants selecting either the feedwater flow or the feedwater pump / valve status logic option, a variable delay timer is to be incorporated into the AMSAC actuation logics. The variable time delay will be inverse to reactor power and will approximate the time that the steam generator takes to boil duwn to the low-low levelsetpointuponalossofmainfeedwater(MFW)fromanygivenreactor l

power level between 40% and 100% power.

The time delay on the C-20 permissive signal for all logics will be lengthened to incorporate the maximum time that the steam generator takes to bofi down to the low-low level setpoint upon a loss of NFW with the reactor operating at 40% power.

The staff considers the Revision 1 chaliges to be acceptable.

Paragraph (c)(6) of the ATWS Rcle requires that detailed information to demon-strate compliance with the requirements be submitted to the Director,) Office of NuclearReactorRegulation(NRR).

In accordance with paragraph (c)(6 of the ATWS Rule, Wisconsin Electric Power Company provided information by letter dated April 23, 1937 (Ref. 4).

The letter forwarded the detailed dasign description of the ATWS mitigating system actuation circuitry proposed for installation at the Point Beach Nuclear Plant, Units 1 and 2.

The staff held conference calls with the licensee on November 18, 1987 and February 25, 1988 to discuss their AMSAC design. As a result of the conference calls, the licensee responded to the staff concerns by letters dated December 30, 1987 (Ref. 5) and March 3, 1988 (Ref. 5).

2.0. REVIEW CRITERIA The systems ana equipment required by 10 CFR 50.62 do not have to meet all of the stringent requirements neally applied to safety-related equipment.

However, the equipment required by the ATWS Rule should be of sufficient quality and reliability to perform its intended function while minimizing the potential for transients that may challenge the safety systems, e.g.,

inadvertent scrams.

The following review criteria were used to evaluate the licensee's submittals:

1.

The ATWS Rule, 10 CFR 50.62.

2.

"Considerations Regarding Systems and Equipment Criteria,"

published in the Federal Register, Volume 49, No. 124, deted June 25, 1984.

3.

Generic Letter 85-06, "Quality Assurance Guidance for ATWS Equipment That Is Not Safety Related."

4.

Safety Evaluation of WCAP-10858 (Ref.1).

5.

WCAP-10858-P-A, Revision 1(Ref.3).

. 3.0 DISCUSSION AND EVALUATION To determine that conditions indicative of an ATWS event are present, the licensee has elected to implement the generic WCAP-10858-P-A AMSAC design associated with monitoring the main feedwater (MP4) pumps and the MFW valves for operational status.

The AMSAC will be initiated if the MFW pumps are stopped or the MFW valves are closed. As stated in the introduction, WCAP-10858-P-A, Revision 1, calls for a variable timer to be incorporated into the AMSAC actuation circuit. The licensee has elected not to incorporate this function, but has c.1osen to retain the 30-second fixed time delay. The con-sequence of the fixed time delay is that at lower power levels AMSAC may cause a turbine trip and subsequent reactor trip prior to an RPS initiated reactor scram at the low-low steam generator level setpoint. The licensee has confirmed that the original plant desige ' Ais provides for turbine trip occurring prior to an RPS initiated reactor (i.e., actuation of an AMSAC-caused turbine trip will appear no different tnan any other turbine trip). Also, this event has been analyzed as a loss of electrical load in FSAR Section 14.1.9.

Many details and interfaces associated with the implementation of the final AMSAC design ire of a plant-specific nature.

In it, 56fety evaluation of WCAP-10858, the staff Identified 14 key elements that require resolution for each plant design. The following paragraphs provide a discussion on the license:e's compliance with respect to 13 of the plant-specific elements.

Tne 14th key element Technical Specifications, will be the subject of future generic action.

1.

Diversity The plant design should include adequate diversity between the AMSAC equipment and the existing Reactor Protection System (RPS) equipment.

Reasonable equipwant diversity, to the extent practicable, is required to minimize the potential for common-cause failures.

The licensee has committed to implement C-20 instrumentation and AMSAC logic hardware which will be diverse from that used in the reactor trip system. AMSAC will use latching relays and time delay relays that are not used in the RPS. The output isolation relays will also be diverse from the relays used in the RPS. The staff 'inds the licensee's commitnent acceptable ::cbject to the satisfactory implementation of diverse AMSAC logic equipment consistent with the ATWY Rule (10 CFR 50.62).

2.

Logic Power Supplies Logic power supplies need not be Class iE but must be capable of parforming the required design functions upon a 19ss of offsite power. Tne logic powee must come from a power source faat is independent from the RPS power supplies.

The licensee has provided information verifying that the logic power supplies used for AMSAC are independent and diverse from the RPS power supplies and will function during the loss of offsite power.

3.

Safety-Releted Interface The implementation of the ATWS Rule shall be such that the existing Reactcr Protection System (RPS) continues to meet all applicable safety criteria.

The proposed Point Beach AMSAC design does not interface with the RPS.

Redundant contacts on the pump motor breakers and the MFW valves will be dedicated to the AMSAC. The only safety-related interface will be between the AMSAC and the AFW circuits. The existing Point Beach safety-related criteria, as applicable to the RPS, will continue to be met. Therefore, subsequent to the implementation of AMSAC, the RPS will perform its required safety function without interference from AMSAC.

Refer to Item 9 for further discussion on this issue.

4.

Quality Assurance The licensee is required to provide infonnation regarding compliance with Generic Letter (GL) 85-06, "Quality Assurance for ATWS Equipment That Is Not Safety Related."

i The criteria of the NRC quality assurance guidance (GL-85-06) were reviewed by the licensee. The licensee stated that the quality assurance practices at the Point Beach plant, as applicable to the nonsafety-related AMSAC 1

equipment, comply with the guidance of GL-85-06, 5.

Maintenance Gypasses Information showing how maintenance at power is accomplished should.be provided.

In addition, maintenance bypass indications should be incorporated into the continuous indication of bypass status in the control room.

The licensee has stated that, during maintenance or surveillance of the AMSAC system or sensor inputs, the AMSAC output signals will be bypassed using a permanently-installed bypass switch located at the AMSAC control panel. Continuous indication of the AMSAC bypass will be provided by the AMSAC trouble status alann window which will be located on the main control board.

6.

Operating Bypasses The operating bypasses should be indicated continuously in the control room. Diversity and independence of the C-20 pennissive signal should be l

provided.

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The licensee has stated that the C-20 permissive signal will be derived from the turbine first stage impulse pressure. The signal will be provided by a pressure transmitter dedicated to the AMSAC and will be diverse from transmitters used in the RPS.

The C-20 signal will disable the AMSAC below 40% reactor power. Above 40% power, the AMSAC will be armed automatically.

On decreasing power, the arming signal will be retained for a nominal 60 seconds after power decrease below the 40% power f.etpoint. The C-20 time deley is consistent with the AMSAC actuation fixed time delay of 30 seconds. The status of the C-20 permissive signal will be continuuusly indicated in the control room via an annunciator window.

/.

Means for Bypasses The means for bypassing snall be accomplished by the use of a pemanently installed, human-factored, bypass switch or similar device. Disallowed methods for bypassing mentioned in the guidance should not be utilized.

The licensee provided infomation stating that bypassing AMSAC during testing and maintenance will be accomplished with a permanently-instal..J bypass switch. The disallowed methods for bypassing, such as lif;ing leads, pulling fuses, blocking relays, or tripping areakers, will not be i

used.

l The licensee has committed to conduct a human-factors review of the bypass controls / indicators consistent with the plant's detailed control room I

l design process.

8.

Manual Initiation Manual initiation capability of the AMSAC function must be provided.

The licensee discussed how manual turbine trip and auxiliary feedwater actuation are accomplished by the operator.

The licensee stated that l

existing manual controla for turbine trip and AFW actuaticn are located in the main control room and will be used by the operator to manually perfom the AMSAC function if necessary. Thus, no additional manual initiation capability is required as a.'esult of installing the AMSAC equipment.

9.

Electrical Independence From Existing Reat. tor Protection System Indr.pendence is required from the sensor output to the final actuation device at which point nonsafety-related circuits must be isolated,from s.sfety-related circuits by qualified Class IE isolators.

l The licensee stated that the inputs to AMSAC will be separate from and independent of the RPS.

The only safety-related interface associated with tne AMJAC will be between the AMSAC and the AFW system. The licensee has infomed the staff that the required isolatlon will be achieved using electrical isolation devices that have been qualified and tested to l

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l Class 1E electrical equipment requirements.

In addition, the isolators will be tested as described in Appendix A to the safety evaluation (Ref.

1).

The information required by Appendix A is to be compiled by the licensee. This information should be available for staff review during a subsequent site audit to be performed by the NRC in accordance with Temporary Instruction. 500/20 (Ref.

7).

10. Physical Separation From Existing Reactor Protection System The implementation of tne ATWS mitigating system must be such that he separation criteria applied to the existing RPS are not violated.

The licensee stated that the AMSAC circuitry will be physically separated from the RPS circuitry. ATWS equipment cabinets will be installed so that there,,111 be no interaction with the protection system cabinets. The existing separation criteria for the RPS will not be compromised as a result of the installation of ANSAC circuitry.

11. Enviroamental Qualification The plant-specific submittal should address the environmental qualifica-tion of ATWS equipnent for anticipated operational occurrences.

The licensee stated that AMSAC mitigation equipment will be environmentally qualified, where required, in accordance with the administrative procedures established at Wisconsin Electric to ensure compliance with the 10 CFR 50.49, "Environmental Qualification of Electric Equipment Important to Safety for Nuclear Power Plants." Other proposed AMSAC equipmnt does not require explicit environmental qualification since it is either located in a mild environment or is not required to operate during or following exposure to potentially harsh environtents resulting from design basis accidents. The AMSAC circuitry will be qualified for all anticipated operational occurrences expected to occur prior to or during an ATWS event.

12. Testability at Power Measuces to test the ATWS mitigating system before Installation, as well as periodically, are to be established. Testing of the system may be perfonned with the system in the bypass mode.

The end-to-end testing, i.e., from sensor through final actuation device, should be perfonned with the plant shutdown.

The licensee scated that a complete end-to-anti test of tne AMSAC system, including the AMSAC outputs through the final actuation devices, will be perfonned during each refueling outage. With the plant at power, the system can be tested with the AMSAC outputs bypassed.

esting of the portions of AMSAC that can be tested at power, such as he bistables, time delays, and logic relays, will be performed semiannut.lly. The output latching relays and th switch contacts on the valve stems and circuit breakers do not lend thernselves te testing except during plant outages.

The licensee has committed to conduct a human-factors review of the controls and indications used for testing purposes consistent with the plant's detailed control room design process.

13.

Completion of Mitigative Action The licensee is required to verify that (1) the protective action, once initiated, goes to completion; and (2) the subsequent return to operation requires deliberate operator action.

The licensee responded that the system design will be such that AMSAC is consistent with the existing circuitry of the auxiliary feedwater and turbine trip control systems and with the blowdown isolation valve trip system. Once initiated, the design (i.e., latching relays, etc.) will ensure that the protective action goes to completion. Deliberate manual dCtion on the part of the operator will be required to reset the turbine trip circuitry and to restore the AFW pumps to standby status.

4.0 CONCLUSION

The staff concludes, based on the above discussion and pending final resolution of the Technical Specification issue, that the AMSAC design proposed by Wisconsin Electric Power Company for the Point Beach Nuclear Plant. Units 1 and 2, is acceptable and is in compliance with the ATWS Rule. 10 CFR 50.62, paragraph (c)(1). The staff's conclusion is further subject to the successful completion of certain noted human factors engineering reviews and satisfactory completion of isolation device qualification testing to which the licensee has committed.

It is the staff's position that the AMSAC should not be declared operational i

l prior to successful qualification of the required electrical isolation devices.

Until staff review is completed regarding the use of Technical Specifications for ATWS requirements, the licensee should continue with the scheduled instal-lation and implementation (planned operation) of the ATWS design utilizing administratively-controlled procedures.

Principal Contributor:

Robert Stevens Date:

August 4, 1988 i

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REFERENCES 1.

Letter, C. E. Rossi (NRC) to L. D. Butterfield (WOG), "Acceptance for Referencing of Licensing Topical P.eport." July 7,1986.

2.

Letter, R. A. Newtun (WOG) to J. Lyons (NRC), "Westinghouse Owners Group Addendum 1 to WCAP-10858-P-A and WCAP-11233-A:

AMSAC Generic Design Package," February 26, 1987.

3.

Letter, R. A. Newton (WOG) to J. Lyons (NRC), "Westinghouse Owners Group Transmittal of Topical Report, WCAP-10858-P-A, Revision 1 AMSAC Generic Design Package," August 3, 1987.

4 Letter, C. W. Fay (WEPCo) to U.S. NRC, "ATWS Mitigating System Actuation Circuitry (AMSAC) Final Design and Implementation Schedules," April 23, 1987.

5.

Letter, C. W. Fay (WEPCo) to U.S. NRC, "Additional Information ATWSMitigatingSystemActuationCircuits(AMSAC),"

December 30, 1987.

6.

Letter, C. W. Fay (WEPCo) to U.S. NRC, "ATWS Mitigating Systems ActuationCircuits(AMSAC),"March 2,1988.

7.

Temporary Instruction 2500/20, "Inspection to Determine Compliar,ce with ATWS Rule,10 CFR 50.62," February 9,1987 1

I l

Mr. C. W. Fay Point Beach huclear Plant Wisconsin Electric Power Company Units 1 and 2 cc:

Mr. Bruce Churchill, Esq.

Shaw, Pittman, Potts and Trowbridge 2300 N Street, N.W.

Washington, DC 20037 Mr. James J. Zach, Manager Point Beach Nuclear Plant Wisconsin Electric Power Company 6610 Nuclear Road Two Rivers, Wisconsin 54241 Town Chairman Town of Two Creeks Route 3 Two Rivers, Wisconsin 54241 Chairman Public Service Commission of Wisconsin Hills Farms State Office Building Madison, Wisconsin 53702 Regional Administrator, Region III U.S. Nuclear Regulatory Commission Office of Executive Director for Operations 799 Roosevelt Road Glen Ellyn, Illinois 60137 Resident Inspector's Office U.S. Nuclear Regulatory Commission 6612 Nuclear Road Two Rivers, Wisconsin 54241 i

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