ML20247M743
| ML20247M743 | |
| Person / Time | |
|---|---|
| Site: | Zion File:ZionSolutions icon.png |
| Issue date: | 05/22/1989 |
| From: | NRC |
| To: | |
| Shared Package | |
| ML20247M725 | List: |
| References | |
| NUDOCS 8906050114 | |
| Download: ML20247M743 (9) | |
Text
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SAFETY EVALUATION. REPORT 30NNUCLEAR.POWERSTATION, UNITS 1.AND.2 r
COMPLIANCE.WITH.ATWS RULE.10.CFR.50.62
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DOCKET NOS.'50 295/304
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 TransientsWithoutScram(ATWS))EventsforLiaht-Water-CooledNucle Plants" (known as the ATWS Rule. The requireitents of Section 10 CFR 50.62 apply to c11 commercial light-water-cooleo nuclear power plants.
An ATWS 1s an anticipated operational occurrence (such at loss of feedwater, loss of condenser vacuum, or loss of offsite power) that is accompanied by a
.f ailure of the Reactor Trip System (RTS) to shut down the reactor. The ATWS Rule requires specific improvements in tne design and operation of commercial nuclear power facilities to reduce the probability of failure to shut down the reactor following anticipated transients and to mitigate the consequences of en ATWS event.
Paragraph (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 ano a turbine trip for ATWS events.
In response to paragraph (c)(1), the Westinghouse Owners Grcup (WOG) developed a set of conceptual ATWS mitigating system actuation circuitry '(AMSAC) designs generic to Westinghouse plants.
WOG issued
' Westinghouse Topical Report WCAP-10858, "AMSAC Generic Design Package," which provided information on ;he various Westinghouse designs.
The staff reviewed WCAP-10858 and issued a Safety Evaluation of the subject topical report on July 7, 1986 (Ret. 1).
In this Safety Evaluation, the staff concluded that the generic designs presented in WCAP-10858 adequately meet the requirements of 10 CFR 50.6?. The approved version of the WCAP is labeled i
I During the course of the staff's review of the proposed AMSAC design, the WOG
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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 F.evision 1 to WCAP-10858-P-A (Ref. 3), which incorporated Addendum 1 changes and provided i
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octails 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 generater takes to boil down to the low-low setpoint upon a loss of MFW with the reactor operating at 40% power. The staff considers the Revision 1 changes to be acceptable.
Paragraph (c)(6) of the ATWS Rule requires that detailed information that Office of Nuclear Reactor Regulation (NRRLdemonstrates compliance with the require In accordance with paragraph of the ATWS Rule, Commonwealth Edison (CE) provioed information by letter dated June 5, 1986 (Rei. 4). The letter forwarded the detailed design description of the AMSAC proposed for installation at the Zicn Nuclear Power Station, Units 1 and 2.
The staff held several conference calls with the licensee between August 1986 and March 1988 to oiscuss the proposed AMSAC design, the impact of Revision 1 on the proposed design, and the isolation devices selected for use in the newly created Class IE to non-Class 1E interfaces.
In addition to the conference calls, the staff forwarded a request for additional information (RAI) to the licensee by letter dated November 17, 1986 (Ref. 5).
The licensee responded to the RAI by letter dated.lanuary 9,1987 (Ref. 6).
In addition to the RAI, the licensee respenced to the conference calls by letters dated February 6,1987 (Ref. 7), July 21,1987 (Ref. 8), February 26, 1988 (Ref. 9), and May 25,1988(Ref.10).
In Reference 10, the licensee selected an AMSAC output isolation relay that was acceptable to the staff and supplied the data for the isolation device as requested by Appendix A to the generic Safety Evaluation (Ref.1) issued by the staff.
2.0. REVIEW CRITERIA The systems and equipment required by 10 CFR 50.62 do not have to meet all of 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 potential for transients that may challenge tha 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.
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2.
" Considerations Regarding Systems and Equipment Criteria,"
l published in the Federal Register, Volume 49, No. 124, dated June 26, 1984.
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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 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
,i the water level is below the low-low level setpoint. The licensee has taken various exceptions to the generic WCAP design since many details and interfaces associated with the implementation of the final AMSAC design are of a plant-specific nature.
The WCAP states that the AMSAC logic circuits should be armed (C-20 permissive) when the reactor reaches the 40% power level and recommends that this arming signal be derived from the turbine first-stage impulse chamber pressure. The WCAP further states that existing sensors and sensor nower supplies may be used to obtain this arming signal. The licen:;ee has elected to derive the C-20 permissive AMSAC arming signal from the existing power range neutron detectors.
The signals from the four detectors will be sent to an auctioneering circuit.
The output of the auctioneering circuit becomes the auctioneered nuclear power (ANP) signal, which will be sent via an electronic isolator to a comparator with a setpoint representative of 40% reactor power.
Upon a decrease of reac+.or power below the 40% power setpoint, the ANP signal will be maintained for a period of 120 seconds. The licensee has stated that this time delay will be sufficient to ensure that AMSAC will perform its function.
The WCAP recommends that the steam generator (SG) blowdown and sample line 1 solation valves be closed by the AMSAC output signal. The licensee has chosen not to include these valves as part of the ATWS mitigation system for the Zion Station. The licensee reasoned that the flow rate from these valves is not significant to the delivered AFW flow rate. Also, the automatic closure of the SG blowdown and sample line isolation valves is not included in the existing reactor protection circuitry associated with the SG inventory control.
In its Safety Evaluation of WCAP-10858, the staff identified 14 key elements that require resolution for each plant-specific design. The following paragraphs provide a discussion on the licensee's compliance with resper.t to each of the plant-specific elements and the deviations from the generic WCAP design.
I 1.
Diversity The plant design should include adequate diversity between the AMSAC equipment and the existing Reactor Protection System (RPS) equipment.
l Reasonable equipment diversity, to the extent practicable, is required j
to minimize the potential for common-cause failures.
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l The licensee will use the existing steari generator (SG) water level sensing instrumentation as input to AMSAC. The licensee has verified that the AMSAC logic circuitry will.be.'of a.different design which will be dherse from the RPS logic circuitrya. The AMSAC output signals will interf ace.with the existing circuitry of the feedwater pump and the turbine trip. This interface will utilize' output relays that will be diverse from the relays used in che RPS.
2.
Logic Power Supplies L
Logic power supplies need not be Class IE, but must be capable of.
L 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 RPS power supplies.
The licensee has provided information verifying that the logic power supplies selected for the Zion AMSAC logic circuit will be independent from'the R?S power supplies and will perform its function subsequent to a.
loss of offsite power. The logic power supplies will be designed and procured to meet the quality assurance guidance of Generic Letter 85-06.
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 licensee has stated that the proposed AMSAC design for the Zion Station will not compromise the existing RPS, including electrical separation and independence. The existing safety criteria will continue to be met after implementationofAMSAC(i.e.,theRPSwillcontinuetoperformitssafety function without interference from AMSAC). Refer to Item 9 for further discussion on this issue.
4.
Quality Assurance The licensee is required to provid information regarding compliance with Generic Letter (GL) 85-06, " Quality Assarance for ATWS Equipment that is not Safety Relateo."
The licensee has stated that the AMSAC equipment will be procured and installed as safety-related equipment. This action will ensure the utilization of the licensee's existing quality proc 2dures which exceed J
the requirements of GL 85-06.
5.
Maintenance Bypasses Information showing how maintenance at power is accomplished should ba provided. Also, maintenance bypass indications should be incorporated into the continuous inoicaticn of bypass status in the control roone.
l The licensee has stated that, during maintenance or surveillance of the AMSAC system or sensor inputs, the AMSAC output signals will be bypassed using permanently installed bypass switches located on the relay, matrices, and testing (RMT) cabinet. The AMSAC bypass will be continuously indicated by a control room annunciator and by a test light located on the PET cabinet.
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 stated that the AMSAC will be automatically bypassed below 40% reactor power. The 40% reactor power setpoint will be determined by the ANP signal and will be raintained for 120 seconds upon a reactor power decrease below 40% power as detected by the power range neutron detectors.
A control room annunciator will be activated when the reactor power is below 40% indicating that the AMSAC is bypassed. The control room operator will also be alerted by the control room annunciator when the SG level channels trip and when the reactor is above 40% power.
7.
Means for Bypasses The means for bypassing shall be accomplished by the use of a permanently installed, human-factored, bypass switch or similar device. Disallowed methods for bypassing mentioned in the guidance should not be utilized.
The licensee stated that bypassing AMSAC during testing and maintenance will be accomplished with a permanently installed bypass switch. The disallowed methods for bypassing such as lif ting leads, pulling fuses, blocking relays, or tripping breakers will not be used.
It is the staff's understanding that the licensee will conduct a human-factors review of the maintenance / operations bypass controls and indications consistent with the plant's detailed control room design process.
8..
Manual Initiation Manual initiation capability of the AMSAC mitigation function must be provided.
The licensee discussed how manual turbine trip and auxiliary feedwater actuation are accomplished by the operator. The licensee stated that existing manual controls for turbine trip and AFW actuation are located in the main control room and will be used by the operator to manually perform a turbine trip and start AFW pumps. Thus, no additional manual initiation capability is required as a result of installing the AMSAC equipment.
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i 9.
Electrical Independence.From Existino Reactor. Protection; System Independence is required from the sensor output to the final actuation device, at which point nonsafety-related circuits must be isolated from
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safety-related' circuits by qualified Class.1E isolators.
The licensee discussed how electrical independence is to be achieved. The proposed AMSAC design requires isolation between the AMSAC and the Class 1E circuits associated with the steam generator' level transmitters, the ANP signal, and the Class 1E AFW pumps.
The licensee has informed the staff that the required isolation will be achieved using electrical isolation devices that have been qualified and
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tested to Class 1E electrical equipment requirements.
In addition, the isolators were qualification-tested as described in Appendix A to.the Safety Evaluation (Ref.1).
- 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.
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The licensee has stated that the AMSAC equipment will be physically separated from the existing RPS and that AMSAC separation will be in accordance with the separation criteria established for the station at the time of initial plant licensing.
In particular, existing separation between the RPS and nonsafety-related circuits will not be compromised by the installation of the AMSAC equipment.
- 11. Environmental Qualification The plant-specific submittal should address the environmental qualifica-tion of ATWS equipment for anticipated operational occurrences.
The licensee has stated that the AMSAC equipment, with the exception of' the steam generator level transmitters, will be located in plant areas ~
designated as mild environment under Zion's EQ program. The equipment being installed in the mild environment areas will not be purchased with any environmental qualification characteristics. The existing steam generator level transmitters are located in a harsh environment and are part of Zion's EQ program. Based on the information provideo, it is the staff's understanding that the AMSAC equipment will be qualified for anticipated operational occurrences associated with the respective equipment location.
- 12. Testability at Power Measures to test the ATWS mitigating system before initial operation 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 the input sensor through to the final actuation device should be performed with the plent shutdown.
. The licensee has proposed two types of tests, an At-Power test and a Zero-Power test. The At-Power test with the Block Test Switch (BTS) in the block position will test from the output of the level transmitters up to the actuating relays without causing an AMSI.C actuation. The bypassed condition will be continuously indicated in the control room. The Zero-Power test will be performed with the plant shutdown. This test will actually demonstrate a start of the AFW pumps and a Turbine Trip.
It is the staff's understanding that the Zero-Power tests will be performed once each refueling outage and that the licensee will 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 is required.
The licensee stated that, once initiated through AMSAC, the completion of mitigative action is consistent with the existing plant turbine trip and with the auxiliary feedwater pump trip and auxiliary feedwater pump trip control circuitry. The circuitry automatically locks in upon initiation and deliberate manual action on the part of the operator is required to reset the circuits. The components will reset only if the ATWS mitigation system actuation signal is no longer present.
- 14. Technical Specifications The plant-specific submittal should address technical specification requirements for AMSAC.
The licensee responded stating 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 ano actions required to service the AMSAC will be administratively controlkd using station procedures.
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 operating and surveillance requirements in the technical specifications.
In its interim Commission Policy Statement of Technical Specification Improvements for Nuclear Power Plants [52 Federal Register 3788, February 6,1987], the Commission established a specific set of objective i
criteria for determining which regulatory requirements and operating restrictions should be included in technical specifications. The staff is presently 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 subject to the results of, the staff's further review. The staff will provide for AMSAC at a later date.
4.0 CONCLUSION
The staff concludes, based on the above discussion and subject to final resolution of the technical specification issue, that the AMSAC design proposed by Connonwealth Edison for the Zion Nuclear Power Station, Units 1 and 2, is acceptable and is in compliancewiththeATWSRule,10CFR50.62, paragraph (c)(1). The staff's conclusion is further subjert to the successful completion of certain noted human-factors engineering reviews.
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Until staff review is completed regarding the use of technica1 specifications for ATWS requirements, the licensee should continue with the scheduleo installation and implementation (planned operation) of the ATWS design and provide testing utilizing administratively controlled procedures.
5.0 REFERENCES
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), " 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, P. C. LeBlond (CE) to H. R. Denton (NRC), " Zion Nuclear Power Station, Units 1 and 2, ATWS Protection - 10 CFR 50.62,"
June 5, 1986.
5.
Letter, S. A. Varga (NRC) to D. L. Farrar (CE), " Zion 10 CFR 50.62 (ATWSRule) Review;RequestforAdditionalInformation,"
November 17, 1986.
l 6.
Letter, P. C. LeBlond (CE) to H. R. Denton (NRC), " Zion Station Units 1 and 2, ATWS Protection - 10 CFR 50.62," January 9,1987.
7.
Letter, P. C. LeBlond (CE) to H. R. Denton (NRC), " Zion Station Units 1 and 2, ATWS Protection - 10 CFR 50.62," February 6, 1987.
8.
Letter, P. C. I.eBlond (CE) to U.S. NRC, " Zion Station Units 1 and 2, ATW5 Protection - 10 CFR 50.62," July 21, 1987.
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9.
Letter, G. E. Trzyna (CE) to U.S. NRC, " Zion Nuclear Power Station, Units 1 and 2, ATWS Protection - 10 CFR 50.62," February 26,'1988.
- 10. Letter, G. E. Trzyna (CE) to U.S. NRC, " Zion Nuclear Power Station, Units.1 and 2, ATWS Protection," May 25, 1988.
Principal Contributor:
L. Tram Dated:
May 22,1989 I
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