ML20244D819

SER Supporting Util ATWS Mitigating Sys Actuation Circuitry Designs

ML20244D819
Person / Time
Site:	Byron
Issue date:	06/13/1989
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20244D817	List: ML20244D813 ML20244D819
References
GL-85-06, GL-85-6, NUDOCS 8906190273
Download: ML20244D819 (12)

Text

_ _ _ _ _ - __ - _ . _ _ _

ENCLOSURE 1 SAFETY EVALUATION REPORT BYRON STATION, UNITS 1 AND 2 j

COMPLIANCE WITH ATWS RULE 10 CFR 50.62 DOCKET N05: 50-454/455 .

1.0 INTRODUCTION

l l

On July 26, 1984, theCodtofFederalRegulations(CFR)was.amendedto include Section 10 CFR 50.62, " Requirements for Reduction of Risk from AnticipatedTransientsWithoutScram(ATWS)EventsforLight-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 nuclear {

power plants.

I 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 ,

l reactor. The ATWS Rule requires specific improvements in the design and I operation of commercial nuclear power facilities to reduce the probability i of failure to shut down the reactor following anticipated transients and to mitigate the consequences of an ATWS event.  !

l l

Paragraph (c)(1) of 10 CFR 50.62 specifies the basic ATWS mitigation l system requirements for Westinghouse plants. Equipment, diverse from the RTS, is required to initiate the auxiliary feedwater (AFW) system and a turbinetripforATWSevents.-Inresponsetoparagraph(c)(1),the WestinghouseOwnersGroup(WOG)developedasetofconceptualATWS mitigating system actuation circuitry (AMSAC) designs generic to j Westinghouse plants. WOG issued Westinghouse Topical Report WCAP-10858, l "AMSAC Generic Design Packago," which provided information on the various '

Westinghouse designs.

8906290273 890613 PDR ADOCK 05000454 P PDC l

-g-The staff reviewed WCAP-10858 and issued a safety evaluation of the subject topical report on July 7,1986 (Ref.1). In this safety I evaluation, the staff concluded that the generic designs presented in 1 WCAP-10858 adequately meet the requirements of 10 CFR 50.62. The approved version of the WCAP is labeled WCAP-10858-P-A.

I 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), which incorporated Addendum 1 changes and provided details on changes associated with a new variable timer and the C-20 time delay. For those plants selecting either the feedwater flow or the feedwater pump / valve status logic options, 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 down to the low-low level setpoint upon a loss of main feedwater (MFW) from any given reactor 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 boil down to the low-low level setpoint upon a loss of MFW with the reactor operating at 40% j power. The staff considers the Revision 1 changes to be acceptable.

Paragraph (c)(6) of the ATWS Rule requires that detailed information to demonstrate compliance with the requirements be submitted to the Director, Office of Nuclear Reactor Regulation (NRR). In accordance with paragraph (c)(6) of the ATWS Rule, Commonwealth Edison Company (CE) (licensee) provided information by letter dated December 12,1986(Ref.4). The letter forwarded the detailed design description of the ATWS mitigating system actuation circuitry proposed for installation at the Byron Station, Units 1 and 2.

Beginning in February 1987, the staff held several conference calls with the licensee with the last call on February 9,1989, to discuss their AMSAC design.

As a result of the conference calls, the licensee responded to the staff concerns by

s letters dated. Hay 11, 1987 (Ref. 5), March 8, 1988'(Ref. 6), July 6, 1988 (Ref. 7), November 9,1988 (Ref. 8) and February 15,1989(Ref.9).-

~

2.0. REVIEW CRITERIA The systems and equipnent required by 10 CFR 50.62 do not have to meet all

. of the stringent requirements normally applied to safety-related Li equipment. - However, the equipment: required by the ATWS Rule should be'of u 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. ,

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

1. The ATWS Rule, 10 CFR 50.62.  ;

I

2. " Considerations Regarding Systems and Equipment Criteria," l published in the Federal Register, Volume 49, No 124 dated June 26, 1984. i

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

4. Safety Ev61uation of WCAP-10858 (Ref.1).

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

I 3.0 DISCUSSION AND EVALUATION To determine that conditions indicative of an ATWS event are present, the-licensee has elected to implement the WCAP-10858-P-A AMSAC design associated with monitoring the steam generator water level and activating the AMSAC when the water level is below the low-low setpoint. Also, the licensee will implement the new time delay (as described in the

~

introduction section) associated with the C-20 permissive consistent with the requirements of Revision 1 to the WCAP.

-5

3. Safety-Related Interface The implementation of the ATWS Rule shall be such that the existing RPS continues to meet all applicable safety criteria.

The proposed AMSAC design interfaces at its input with the existing Class IE circuits of the steam generator narrow range water level instrumentation and turbine first-stage impulse chamber pressure instrumentation. At its output, the AMSAC will interface with the Class IE circuits of the AFW pumps. Connections with the AFW control circuits will be made downstream of approved Class IE isolation devices. The licensee has confirmed to the staff that the existing safety-related criteria that are in effect at the Byron Station will continue to be met after the implementation of AMSAC (i.e., the RPS will continue to perform its safety functions without interference from AMSAC). Refer to Item 9 for further discussion on this issue.

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

The criteria of the NRC quality assurance guidance (GL 85-06) were reviewed by the licensee. The licensee stated that quality assurance practices at the Byron Stations, as applicable to nonsafety-related AMSAC equipment, comply with the guidance of GL 85-06 and other Commonwealth Edison Company quality control requirements.

5. Maintenance Bypasses 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 provided information showing how maintenance is to be accomplished at power. -The staff was informed that maintenance'at power will be performed by inhibiting (through a permanently installed switch) the operation of AMSAC.'s output relays, which will

-block the output signal and, thus, prevent'it from reach.ng the final actuation devices. The continuous . indication of bypass _ status will be.provided in the main control room through the use of status lights and alarms. It'is the staff's' understanding that the: licensee-will: conduct a human-factors review-of_the subject indication consistent with the plant's control room design process.

6. Operating Bypasses The operating bypasses should be indicated continuously. in the control room. The independence of the C-20 permissive signal should be addressed.

The licensee has provided information stating that_the AMSAC-operating bypass (C-20) will be used to enable the operators to bring.

the plant up in power during startup and to avoid spurious AMSAC actuations at power levels below 40% reactor" power (the C-20 arming setpoint). Above 40% reactor-power, the C-20 will automatically arm the AMSAC logics. The C-20 permissive signal will originate from existing first-stage turbine impulse chanber. pressure sensors.

Upon a turbine trip. (loss of the load ATWS),' the permissive signal will be maintained by a timer for a period of 360 seconds consistent-with Revision 1 to WCAP-10858-P-A. The licensee has determined that this time delay will be sufficient to ensure that AMSAC will perform its function. The C-20 pennissive signal will be taken downstream from qualified isolators and will not' interfere with the RPS. The operating L

bypass will be indicated continuously in the control room via annunciation

I U 3. .

,i and statusLlights and will be consistent with the existing' bypass'-

design philosophy used in the control room. It is'the: staff's.

understanding that the licensee will' conduct a human-factors reviewi of the-subject indication ~ consistent with the p1' ant's control' room design: process..-

^ '

'_7 .. Means'for Bypasses The means for bypassing shall be accomplished by using'a permanently:

. installed, humar.-factored, bypass! switch or similar device.=

Disallowed methods for bypassing: mentioned in the guidance should not be utilized.

.The licensee's response stated that a permanently installed control.

switch will be used for the bypass function. The' disallowed methods for bypassing, such as lifting leads, pulling fuses, blocking relays,.

or tripping breakers will.not be used. The bypass switch will be located in the AMSAC cabinet.

It is the staff's understanding that.the licensee will conduct a human-factors review of the AMSAC bypass controls. consistent with the plant's detailed control room design process. . :,

a d

8. Manual Initiation Manual initiation capability of the AMSAC mitigation function' at the - i system level must be provided.- 1 In the plant-specific submitt'al, the licensee stated that the

~

operator can use existing manual controls to perform a turbine trip l and to start auxiliary feedwater flow should it be necessary. Thus, no additional manual initiation capability will be required as a- 1 result of installing the AMSAC equipment. ]

i l

l a

s 8-

9. Electrical Independence From Existing Reactor Protectio'n System Independence is required from the sensor output to the final _

actuation device, at which point- nonsafety-related: circuits must be isolated from safety-related circuits by qualified Class 1E ,

isolators..

The licensee discussed how' electrical independence is to be achieved. The proposed design requires isolation between-the non-Class 1E AMSAC and the Class 1E circuits associated with the-steamgenerator(SG) level,-theturbinefirst-stageimpulsechamber-pressure signals, and the AFW circuits. -The licensee hasLinformed ,

.thestaffthattherequiredisolationwillbeachievedlusing electrical isolation' devices that have been qualified and tested to Class IE electrical equipment. requirements. . In addition, the-isolators were tested as described in Appendix A to the staff's. safety evaluation (Ref.1). The voltage and current test values used in the testing of the isolators encompass the circuit values presently existing in the AMSAC circuits at the Byron station.

10. Physical Separation From Existing Reactor Protection System The implementation of the ATWS mitigating system must be such that the 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. The licensee has further stated that the cable routing will be independent of protection system cable routing'and that the ATWS equipment' cabinets will be located so that there will be no interaction with the' protection system cabinets.

The licensee also stated that the RPS design will continue l

(subsequent to the implementation of AMSAC) to meet the separation criteria originally established for the Byron station during original plant licensing.

1

__ _ _ _ - - a

--g _-

11. Environmental Qualification The plant-specific submittal shcdid address.'the environmental q'alification u of ATWS equipment for.. anticipated operational occurrences.

The licensee: stated that.AMSAC mitigation equipment will be located-in areas of the plant that are considered to.be a mild environment.

~The licensee.also stated that the. equipment will be designed to perform.its function during anticipated' operational occurrences that.

might occur associated with the respective; equipment' locations.:

12. Testability at' Power Measures to test the ATWS mitigating system before'insta11ation, as well as periodically, are to be established. Testing of the system--

may be performed with the system in the bypass mode. Testing from-the input sensor through to the final actuation device should be performed with the plant shut down.

The licensee stated that a complete end-to-end test of the AMSAC.

system, including the ANSAC outputs through to the final actuation devices, will be performed during each refueling outage. With the plant at power, the system will be tested with the AMSAC' output

. actuation devices bypassed. The testing capability consists of a-series of overlapping tests. These tests will verify analog. channel

. accuracy, setpoint'(bistable trip) accuracy, coincidence logic' operation, and ' operation and accuracy of all timers. The at-power logic tests will be performed once every six months.

The bypass of the AMSAC output actuation devices will be accomplished

.through a' permanently installed bypass switch which will negate the need L to lift leads, pull fuses, trip breakers, or physically block-relays. Status outputs to the main control board, indicating that a general warning. condition exists with AMSAC, will be initiated when I

e l

1

9

r

]

- 10 e the system's outputs are bypassed. Test procedures will be used to test the AMSAC circuitry and outputs. .These procedures will ensure l that AMSAC is returned to service when testing is complete.

It is the staff's understanding that-the licensee will conduct a j human-factors review of the controls and indications used for testing purposes that is consistent with the plant's detailed control room'

. design process.

13 '. Completion of Mitigative Action i

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 L] 1 is consistent with the circuitry of the auxiliary feedwater and I turbine trip control systems. Once' initiated, the design will ensure l that protective action goes to completion. Deliberate operator action will be required to return the final actuation devices to normal operation.

j l

14. Technical Specifications i

• 1 The plant-specific submittal should address technical specification requirements for AMSAC.

L q

The licensee responded that no technical specification action is proposed with respect to the AMSAC. The licensee stated that the system does not meet NRC criteria for inclusion in the technical '

specifications. The surveillance interval and' actions. required to  ;

service the AMSAC will be administrative 1y controlled using station l procedures. '

I .

. t.

- The equipment required by the ATWS Rule to reduce the risk; associated with an ATWS event must be designed to perform,its functions in a reliable manner. A method acceptable to the staff for demonstrating that the

~

equipment satisfies the reliability requirements of the ATWS Ruie~ is to provide limiting conditions for operation and surveillance requirements in the technical specifications.

In its Interim Commission Policy Statement of Technical Specification

.ImprovementsforNuclearPowerPlants[52FederalRegister3788, February 6,1987], the Commission established-a specific set of objective criteria for determining which regulatory requirements and operating restrictions should be included in technical specifications.. The staff is currently reviewing ATWS requirements to criteria in this Pol' icy Statement to determine whether and to what extent technical specifications are j appropriate. Accordingly, this aspect of the staff review remains open d pending completion of, and subject to the results of, the staff's further )

review. The staff will provide guidance regarding the technical l

specification requirements for AMSAC at a later date.

4.0 CONCLUSION

, The staff concludes, based on the above discussion and pending to final resolution of the technical specification issue, that the AMSAC design proposed by the Commonwealth Edison Company for the Byron Station, Ur.its 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 % man-factors engineering reviews.

Until staff review is completed regarding the use of technical  ;

specifications for ATWS requirements, the licensee should continue with  ;

the scheduled installation and implementation (planned operation) of the ATWS design utilizing administrative 1y controlled procedures.  !

l l

I

i

, l 5.0- REFERENCES

s

1. Letter, C. E. Rossi (NRC) to L. D. Butterfield (WOG)- " Acceptance for

~

Referencing of Licensing Topical Report," July 7, 1986.~  !

2. Letter,R.A. Newton (WOG)to'J.Lyons(NRC),"WestinghouseOwners' Group Addendum'1 to WCAP-10858-P-A and WCAP-11233-A: AMSAC Generic Design Package," February 26, 1987.

l

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. 1 l

4. Letter,P.C.LeBlond(CE)toH.R.Denton(NRC),"ATWSProtection-10 CFR 50.62,"' December 12, 1986. '

5.- Letter,P.C.LeBlond(CE)toU.S.NRC,"ATWSProtection-10 CFR 50.62," May 11, 1987.

6. Letter,P.C.LeBlond(CE)toU.S.NRC,"ATWSProtection-10 CFR 50.62," March 8, 1988.

7. Letter, R. A. Chrzanowski (CE) to T. E. Murley (NRC), "ATWS Protection - 10 CFR 50.62," July 6, 1988.

8. Letter,R.A.Chrzanowski(CE)toU.S.NRC,"ATWSProtection- 1 10 CFR 50.62," November 9, 1988. '

9. Letter, S. C. Hunsader (CE) to T. E. Murley (NRC), "ATWS Protection.- I 10 CFR 50.62," February 15, 1989.

I 1

1

- _ - _ - _ _ _ _ - _