ML20247D147
| ML20247D147 | |
| Person / Time | |
|---|---|
| Site: | Braidwood  |
| Issue date: | 07/18/1989 |
| From: | NRC |
| To: | |
| Shared Package | |
| ML20247D142 | List: |
| References | |
| GL-85-06, GL-85-6, NUDOCS 8907250057 | |
| Download: ML20247D147 (14) | |
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ENCLOSURE 1 )
li SAFETY _ EVALUATION REPORT l BRAIDWOOD STATION, UNITS 1 AND 2 1
COMPLIANCE WITH ATWS RULE 10 CFR 50.62 -l DOCKET NOS: 50-456/457 l 1 l I
1.0 INTRODUCTION
On July 26, 1984, the Code of Federal Regulations (CFR) was amended to include Section 10 CFR 50.62, " Requirements for Reduction of Risk from Anticipated 3
1 TransientsWithoutScram(ATWS)EventsforLight-Water-CooledNuclearPower I
Plants" (known as the ATWS Rule). The requirements of Section 10 CFR 50.62
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apply to all ccmmercial light-water-cooled nuclear power plants. ;
1 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 l
failure of the Reactor Trip System (RTS) to shut-down the t. actor. The ATWS
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Rule requires specific improvements in the design and operation of connercial l
nuclear power facilities to reduce the probability of failure to shut down the I 1
reactor following anticipated transients and to mitigate the consequences of an ATWS event.
Paragraph (c)(1) of 10 CFR 50.62 specifies the basic ATWS mitigation system- I requirements for Westinghouse plants. Equipment, diverse from the RTS, is ,
required to initiate the auxiliary feedwater (ATW) 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 l
' Westinghouse Topical Report WCAP-10858, "AMSAC Generic Design Package," which '
provided information on the various Westinghouse designs.
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l l The staff reviewed WCAF-10858 and issued a safety evaluation of the subject l topical report on July 7,1986 (Ref.1). In this safety evaluation, the staff concluded thM the generic designs presented in WCAP-10858 adequately meet the requirements of 16 CFR 50.62. The approved version of the WCAP is labeled
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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 i 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 tinie 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% power. The staff considers the Revision I 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, OfficeofNuclearReactorRegulation(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 Braidwood 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
i concerns by letters dated May 11,1987(Ref.5), March 8,1988(Ref.6),
July 6,1988 (Ref. 7), November 9,1988 (Ref. 8), and February lo,1989 l (Ref.9).
2.0. REVIEW CRITERIA i The systems and equipment required by 10 CFR 50.62 do not have to meet all of l the stringent requirements normally 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 l potential for transients that mcy challenge the safety systems, e.g., I inadvertent scrams.
1 The following review criteria were used to evaluate the licensee's submittals: 1
- 1. The ATWS Rule, 10 CFR 50.62.
- 2. " Considerations Regarding Systems and Cquipment Criteria," published in the Federal Register, Volume 49, No. 124, dated June 26, 1984.
- 3. Generic Letter 85-06, " Quality Assurance Guidance for ATWL 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 l 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
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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.
Hany details and interfaces associated with the implementation of the final AMSAC design are of a plant-specific nature. In its safety 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 licensee's compliance with respect to each of the plant-specific elements.
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- 1. Diversity The plant design should include adequate diversity between the AMSAC equipment and the existing Reactor Protection System (RPS) equipment.
Reasonable equipment diversity, to the extent practicable, is required to minimize the potential for common-cause failures.
The licensee has provided information to confirm that the AMSAC logic circuits will be diverse from the RPS in the areas of design, equipment, and manufacture. Where similar types of components are used, such as output relays, the AMSAC will utilize a relay of a different make and manufacturer
- 2. Locic Power Supplies Logic power supplies need not be Class IE, but must be capable of performing the required design functions upon a loss of offsite power.
The logic power must come from a power source that is independent from the l RPS power supplies.
l l The licensee has provided information verifying that the logic power supplies selected for the Braidwood Station AMSAC logic circuits will
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. I provide the maximum available independence from the RPS power supplies. {
The AliSAC will be powered from nonsafety-related power supplies which will :
be independent of the RPS and capable of operating upon a loss of offsite I power.
- 3. Scfety-Related Interface The implementation of the ATWS Rule shall be such that the e.xisting RPS continues to meet all applicable safety criteria.
The proposed AliSAC 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 AliSAC will interface with the Class IE circuits of the AFW pumps. Connections with the AFW control circuits will be made dcwnstream 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 Braicwood 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 AliSAC). Refer to Item 9 for further discussion en 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 Braidwood Stations, as applicable te nonsafety-related
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1 AMSAC equipment, comply with the guidance of GL 85-06 and other Commonwealth Edison Company quality control requirements. j,
- 5. Maintenance Bypas,ses 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. l The licensee provided information showing how maintenance is to be accomplished at power. The staff was informed that maintenance at power i will be performed by inhibiting (through a permanently installed switch) !
i the operation of AMSAC's output relays, which will block the output signal j and, thus, prevent it from reaching the final actuation devices. The continuous indication of bypass status will be provided in the main j control room through the use of status lights and alarm. It is the I staff's understanding that the licensee will conduct a human-fsetors review of the subject indication consistent with the plant's control room i design process.
- 6. Operating Bypasses l The operating bypasses should be indicated continuously in the control l room. The independence of the C-20 permissive signal should be addressed.
I 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 l in power during startup and to avoid spurious AMSAC actuations at power levels below 40% reactor power (the C-20 arming setpoint). Above 40%
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l reactor power, the C-20 will automatically arm the AMSAC logics. The C-20 permissive signal will originate from existing first-stage turbine impulse chamber pressure sensors. Upon a turbine trip (loss of-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 permissive signal will be taken downstream from qualified isolators and will not interfere with the RPS.
The operating bypass will be indicated continuously in the control room via annunciation and status lights and will be consistent.with the existing bypass design philosophy used in the control room. It is the )
j staff's understanding that the licensee will::onduct a human-factors-review cf the subject indication consistent with the plant's contrcl room design process.
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- 7. Means for Bypasses )
The means for bypassing shall be accomplished by using a permanently installed, human-factored, bypass switch or.similar device. Disallowed 4
methods for bypassing mentioned in the guidance should not be utilized.
l The licensee's response stated that a permanently installed control switch will be useo for the bypass function. The oisallowed methods for-bypassing, such as lifting leads, pulling fuses, blocking relays, or I tripping breakers will not be used. The bypass switch will be located in the AMSAC cabinet, l
i 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, i 1
- 8. Manual Initiation I l
Manual initiation capability of the AMSAC. mitigation function at the system level must be provided.
i In the plant-specific submittal, the licensee stated that the operator can- )
l use existing manual controls to perform a turbine trip and to start 1 l auxiliary feedwater flow should it be necessary. Thus, no additional .
manual initiation capability will be required as a result of installing ;
the AMSAC equipment. l i
- 9. Electrical Independence From Existing Reactor Protection System l
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 IE isolators.
The licensee discussed how electrical independence is to be achieved. The proposed design requires isolation between the non-Class IE AMSAC and the Class IE circuits associated with the steam generator (SG) level, the turbine first-stage impulse chamber pressure signals, and the AFW circuits. The licensee has informed the staff that the required isolation will be achieved using 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 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 Braidwood station.
- 10. Physical Separation From Existing Reactor Protection System The implementation of the ATHS mitigating system must be such that the separation criteria applied to the existing RPS are not violated.
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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 (subsequent to the implementation of l AMSAC) to meet the separation criteria originally established'for the {
Braidwood Station during original plant licensing. 4
- 11. Environmental Qualification 1 The plant-specific submittal shculd address the environmental 1 qualification 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-asscciated with the respective equipment locations.
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- 12. Testability at Power 3
Hessures to test the ATWS mitigating system before installation, 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 to ;
the sensor through to the final actuation device should be performed with '
the plant shut down.
i The licensee stated that a complete end-to-end test of the AMSAC system, including the AMSAC outputs through to the final actuation devices, will j be performed during each refueling outage. With the plant at power, the system will be tested with the AMSAC output actuation devices bypassed.
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q 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 accompushed j l through a permanently installed bypass switch which will negate the need to lift leads, pull fuses, trip breakers, or physically block relays.
Status cutputs to the main control board, indicating that a general warning condition exists with AMSAC, will be initiated when the system's-outputs are bypassed. [TestprocedureswillbeusedtotesttheAMSAC !
circuitry and outputs. These procedures will ensure that AMSAC is returned to service when testing is complete.]
It is the staff's understanding that the licensee will conduct a human-factors review of the controls and indications used for testing purposes that is consistent with the plant's detailed control room design process.
l 13. Completion of Hiticative 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 circuitry of the auxiliary feedwater and turbine trip control systems. Once inithted, the design will ensure that protective '
action goes to completion. Deliberate operator action will be required to return the final actuation devices to normal opera; ion.
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- 14. Technical Specifications I i
The plant-specific submittal should address technical specification requirements for AMSAC.
The licensee responded that no Technical Specification action is proposed l with respect to the AMSAC. The licensee stated that the system does not l meet NRC criteria for inclusion in the technical specifications. The surveillance interval and actions required to service the AMSAC will be administratively controlled using station procedures, j i
i In its Interim Commission Policy Statement of Technical Specification l Improvements for Nuclear Power Plants [52 Federal Register 3788, February 6, l
1987],theCommissionestablishedaspecificsetofobjectivecriteriafor determining which regulatory requirements and operating restrictions should be incluced in technical specifications. The staff is currently reviewing ATWS requirements to criteria in this Policy Statement to determine whether and to what extent technical specifications are appropriate. Accordingly, this aspect of the staff review remains open pending completion of, and l subject to the results of, the staff's further review. The staff will provide guidance regarding the technical specification requirements for AMSAC at a later date.
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 Rule is to provide limiting conditions for operation and surveillance requirements in the technical specifications.
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4.0 C0f!CLUSION The staff concludes, based on the above dircussion ind pending resolution of the technical specification issue, that the AMSAC design proposed by the Commonwealth Edison Company for the Braidwood Station, 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 y of certain noted 'm' factors engineering reviews. Until staff review is completed regardin; -
se of technical specifications for ATWS requirements, .j the licensee should continue with the scheduled installation and implementation ]
(planned operation) of the ATWS design utilizing administratively controlled procedures. '
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5.0 REFERENCES
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- 1. Letter, C. E. Rossi (NRC) to L. D. Butterfield (WOG), " Acceptance for .
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Referencin5 of Licensing Topical Report," July 7, 1986.
- 2. L=tter, R. A. Newton (WOG) to J. Lyons (NRC), " Westinghouse Owners' Group Addendum 1 to WCAP.10858-P-A and WCAP-11233-A: AMSAC Generic f
Design Package," February 26, 1987.
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- 3. Letter, R. A. Newton (WOG) to J. Lyons (NRC), " Westinghouse Owners' Group Transmittal of Topical Report, WCAP-10858-P-A, Revision 1, AK S Generic Design Package," August 3, 1987.
4 Letter, P. C. LeBlond (CE) to H. R. Denton (NRC), "ATWS Protection -
10 CFR 50.62," December 12, 1986.
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10 CFR 50.62," Nay 11, 1987.
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10 CFR 50.62," March 8, 1988.
- 10 CFR 50.62," July 6,1988.
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10 CFR 50.62," November 9, 1988. l l
, 9. Letter, S. C. Hunsader (CE) to T. E. Murley (NRC), "ATWS Protection -
1 10 CFR 50.62," February 15, 1989.
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.. /_ July- 28v 1989 '
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L Docket Nos. . : 50-456 and 50-457.
u Mr. Thomas J. Kovach - i Nuclear Licensing Man 6ger '
Conmionwealth Edison Company Post Office Box 767 Chicago, Illinois .60690
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Dear Mr; Kovach:
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SUBJECT:
ATWS.-RULE (10CFR50.62)-BRAIDWOODSTATION(TACNOS.64035' !
lAND64062) .
1 Enclosed is the~ Safety Evaluation Report associated with the proposed. .!
- implementationoftheATWSRule-(10CFR50.62).. requirements'asrelatedto Braidwood-Station Units 1 and 2.
.i The NRC staff has concluded, pending final resolution of the technical . -
specification issuc,:that the ATWS design that you preposed is in' compliance with the ATWS Rule: requirements of 10 CFR 50.62,- paragraph (c)(1). .The' l staff's conclusion'is based on the successful completion of certain noted. I human-factors engineering' reviews. Until the staff'screview'of.the technical.. -
specification issue is completed, Conmionwealth Edison Company should continue- ,
with the scheduled installation and implementation-(planned operation) of' J the ATWS design using administrative procedures.-
Sincerely, Stephen P. Sands, Project Manager Project Directorate.III-2
] 1 Division of Reactor Projects - III, j
.IV, V, and Special Projects
Enclosure:
As stated cc w/ enclosure: a See next page l
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