ML20237H171
| ML20237H171 | |
| Person / Time | |
|---|---|
| Site: | Grand Gulf  |
| Issue date: | 08/21/1987 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20237H161 | List: |
| References | |
| GL-85-06, GL-85-6, NUDOCS 8709030145 | |
| Download: ML20237H171 (7) | |
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/[DQ080pk UNITED STATES y
g NUCLEAR REGULATORY COMMISSION 5
-j WASHINGTON, D. C. 20555
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SYSTEMS-TO MITIGATE AN ATWS GRAND GULF NUCLEAR STATION, UNIT 1 1
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 Transients Without Scram (ATWS) Events for Light-Water-Cooled Nuclear Power Plants" (known as the "ATWS Rule"). An ATWS is an expected operational transient (such as loss of feedwater, loss of condenser vacuum, or loss of offsite power) which is accompanied by a failure of the reactor trip system (RTS) to shutdown the reactor. The ATWS Rule requires specific improvements in the design and operation of comercial nuclear power facilities to reduce the likelihood of failure to shutdown the reactor following anticipated transients, and to mitigate the consequences of an ATWS event.
Each boiling water reactor (BWR) is required by 10 CFR 50.62 to have three systems to mitigate the consequences of an ATWS event.
1.
It must have an alternate rod injection (ARI) system that is diverse (from the reactor trip system) from sensor output to the final actuation devices. The ARI system must have redundant scram air header exhaust valves. The ARI system must be desi reliable manner and be independent (gned to perfom its function in afrom the exis from sensor output to the final actuation device (Paragraph (c)(3)).
2.
It must have a standby liquid control system (SLCS) with a minimum flow capacity and boron content equivalent in control capacity to 86 gallons per minute of 13 weight percent sodium pentaborate solution. The SLCS and its injection location must be designed to perform its function in a reliablemanner(Paragraph (c)(4)).
3.
It must have equipment to trip the reactor coolant recirculating pumps automatically under conditions indicative of an ATWS. This equipment must be designed to perfom its function.in a reliable manner (Paragraph (c)(5)).
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, this equipment is part of the broader class of structures, systems, and components important to safety defined in the introduction to 10 CFR 50, Appendix A,-General Design Criteria (GDC)..GDC-1 requires that " structures, systems, and components 8709030145 070821 PDR ADOCK 05000416 l
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I important to safety shall be designed, fabricated, erected, and tested to quality standards commensurate with the importance of the safety functions to be perfomed." Generic Letter 85-06 " Quality Assurance Guidance for ATWS Equipment that is not Safety Related" details the quality assurance that must be applied to this equipment.
In general, the equipment to be installed in accordance with the ATWS Rule is required to be diverse from the existing RTS, and must be testable at power.
This equipment is intendeti to provide needed diversity (where only minimal diversity currently exists in the RTS) to reduce the potential for comon mode failures that could result in an ATWS leading to unacceptable plant conditions.
The criteria used in evaluating the licensee's submittal include supplementary information for the ATWS Rule entitle'd " Considerations Regarding Systems and Equipment Criteria" published in the Federal Register (49 FR ?6040) on June 26, 1984, and Generic Letter 85-06 " Quality Assurance Guidance for ATWS Equipment that is not Safety Related."
The licensee for the Grand Gulf Nuclear Station (GGNS)* is a participant in the BWR Owners' Group program for considering ATWS Rule implementation al ternatives. General Electric, on behalf of the BWR Owners' Group, submitted f
a licensing topical report NEDE-31096-P " Anticipated Transients Without l
Scram; Response to NRC ATWS Rule 10 CFR 50.62" dated December 1985 which proposed design concepts to satisfy the ATWS Rule requirements for BWRs. The NRC staff has completed its evaluation of this topical report. By letter dated October 21, 1986 from Gus Lainas (NRC) to Terry A. Picking (BWR Owners' Group) the NRC staff provided its generic safety evaluation report (SER) on NEDE-31096-P.
The staff found NEDE-31096-P to be acceptable for referencing in license applications subject to conditions delineated in the report and the SER.
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By letter dated October 14, 1985, the licensee provided infomation regarding I
the proposed design of ATWS-related equipment for GGNS Unit 1 and comitted to implement the requirements of the ATWS Rule prior to startup following the second refueling outage. The NRC staff requested additional infomation by letter dated February 11, 1987. By letters dated April 3 and June 22, 1987, the licensee responded to staff requests, referenced selected design concepts in topical report NEDE-31096-P and described how the GGNS Unit 1 ATWS-related equipment meets the requirements identified in the staff's SER of the topical report.
In accordance with its October 21, 1986 letter transmitting the generic SER on topical report NEDE-31096-P, the NRC staff did not perform a detailed review of GGNS Unit 1 ATWS-related equipment described in the licensee's submittals because the licensee endorsed the design concepts in NEDE-31096-P and provided plant-specific information to demonstrate compliance with the
- 0n December 20, 1986, the Comission authorized the transfer of control and perfomance of licensed activities for Grand Gulf Nuclear Station from Mississippi Power & Light Company to System Energy Resources, Inc. (SERI).
"The licensee" refers to Mississippi Power & Light Company before December 20, 1986 and to SERI on or after December 20, 1986.
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requirements in the staff's generic SER on NEDE-31096-P. The staff's evaluation of the standby liquid control system (SLCS), alternate rod injection (ARI) and recirculation pump trip (RPT) features against the requirements in the staff's generic SER are provided in the following subsections.
2.0 EVALUATION l
2.1 Alternate rod injection ARI system The licensee's April 3, 1987 letter provided information regarding the conformance of the GGNS Unit 1 ARI system with approved design features identified in Appendix A to the staff's generic SER on NEDE-31096-P. The following subsections provide the sta,ff's evaluation of the GGNS Unit 1 ARI l
design features.
(1) ARI system function time j
The licensee stated that the number, size, and location of the ARI vent paths have been selected such that the scram pilot air header will be depressurized, the scram inlet and outlet valves will be opened, and rod l
l travel will be initiated within 15 seconds. This will be verified by
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tests following installation of the ARI system to demonstrate that the ARI vent paths will depressurize the scram pilot air header to less than 18 psig within 15 seconds. Rod insertion times are currently verified by Technical Specification surveillance procedures to be significantly less than 10 seconds.
Consequently, the ARI system function will be completed in less than 25 seconds.
The staff finds this meets the requirements in Appendix A to the staff's generic SER on NEDE-31096-P and therefore is acceptable.
(2)
Safety-related requirements The ATWS Rule does not require the ARI system to be safety-grade, but the implementation mu::t be such that the existing protection system continues to meet all applicable safety-related criteria. The Grand Gulf ARI system is classified as a nonsafety-related system which does not conform to all the requirements of IEEE Std-279. However, the ARI system will use separate sensors, logic circuitries, cabinets, and scram valves. There will be no direct interface between the ARI system and the existing protection system. Therefore, the implementation of the ARI system will allow the existing protection system to continue to meet all applicable safety-related criteria. The staff finds this meets Appendix A to the staff's generic SER and therefore is acceptable.
(3) Redundancy The licensee stated that the ARI valves will be redundant to the backup scram valves. The ARI system will perfonn a function redundant to the backup scram system. The staff finds this meets Appendix A to the staff's generic SER and therefore is acceptable.
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I (4) Diversity from existing RTS j
The licensee stated that the ARI system will be diverse (functional and l
component) from the existing RTS. The ARI system will be energized-to-function instead of deenergized-to-function for RTS. The ARI system will use DC power instead of AC power for the scram system. The ARI system actuation sensors (the high dome pressure or the low vessel water level) will be diverse from the RTS. The ARI initiation logic (two-out-of-two) will be diverse from the RTS logic (one-out-of-two twice). The staff finds this meets Appendix A to the staff's generic SER and therefore is acceptable.
1 (5) Electrical independence from the existing RTS The licensee stated that the ARI circuitry will be powered by two non-divisional 125 VDC power circuits which are not utilized by the existing.
reactor trip system. The reactor trip system is powered from dedicated 120 VAC reactor protection system buses. The staff finds this meets Appendix A to the staff's generic SER and therefore is acceptable.
(6) Physical separation from the existing RTS The licensee stated that the ARI system will be physically separated from the RTS. The ARI logic components will be located in different cabinets from the RTS. The cable and wiring will be physically separated from the RTS. The staff finds this meets Appendix A to the staff's
. generic SER and therefore is acceptable.
(7)
Environmental Qualification The licensee stated that the ARI equipment will be qualified to conditions during an ATWS event up to the time the ARI function is completed. The staff finds this meets Appendix A to the staff's generic SER and therefore is acceptable.
(8) Quality Assurance The licensee stated that in order to comply with the QA guidance provided in Generic Letter 85-06, SERI will include the ATWS nonsafety-related equipment in Appendix B of the GGNS Q-List prior to startup following the second refueling outage. Appendix B identifies nonsafety-related equipment which has special QA requirements. The staff finds this meets Appendix A to the staff's generic SER and therefore is acceptable.
(9) Safety-related power supply The ATWS Rule requires that the ARI system perfonn its safety function upon loss of offsite power, and that the power source be independent from the existing reactor trip system. The licensee stated that the ARI circuitry is powered by two non-divisional 125 VDC power circuits which are not utilized by t.he existing reactor protection system (RPS).
The staff finds that the ARI design is capable of perfonning its safety i
s,
i functions with loss of offsite power and the ARI power sources are independent from the existing RPS power source. This meets Appendix A to the staff's generic SER and therefore is acceptable.
(10)TestabilityatPower The licensee stated that the ARI system is designed to pemit electrical maintenance, calibration and testing during nomal operation. The trip i
logic and solenoid valves may be tested by placing one half of the circuitry in a test mode by means of a switch at the local test panel.
Maintenance and calibration of the system may be accomplished during nomal operation without impairing the system's design capability.
Manual / automatic trip initiation, of the system may still be initiated during maintenance, calibration and testing since the trip signal will bypass the out-of-service component, or in the case of the circuit being tested, the trip signal will override the test signal.
If power is removed from either the inboard or outboard valves or the control logic for either during a maintenance function, the function of the ARI circuit will not be completed.
During such an occurrence the inoperative status-of the affected circuitry is displayed both in the control room and at the local panel. The staff finds this meets Appendix A to the staff's generic SER and therefore is acceptable.
(11) Inadvertent Actuation The licensee stated that the ARI design utilizes coincident logic.
In each division, both channels must be tripped in order to initiate the mitigative actions. The ARI actuation setpoints will not challenge scram setpoints. The staff finds this meets Appendix A to the staff's generic SER and therefore is acceptable.
(12) Manual Initiation The licensee stated that the manual initiation capability is provided.
The staff finds this meets Appendix A to the staff's generic SER and therefore is acceptable.
l (13) Infomation Readout The licensee stated that the ARI system status indication will be provided in the main control room and at the local test panel. System status lights and test switches at the local test panel will provide indication as to the system's condition and its capability to perfom its design function.
The ARI system will have the following control room indications: READY TO RESET, INITIATION, IN TEST, ARMED, and OUT OF SERVICE. The staff finds this meets Appendix A to the staff's generic SER and therefore is acceptable.
(14) Completion of protective action once it is initiated The licensee stated that the ARI design has a seal-in feature to ensure the completion of protective action once it is initiated. After initial conditions return to normal, deliberate operator action is required to reset the safety system logic to normal. The staff finds this meets Appendix A to the staff's generic SER and therefore is acceptable.
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. q In sumary, the staff concludes that the GGNS Unit 1 ARI design features l
meet the ARI design basis requirements approved by the staff in the generic j
l SER on NEDE-31096-P.
In its generic SER, the staff concluded that licensees J
who meet these ARI design bases requirements will be considered to be in compliance with Paragraph (c)(3) of 10 CFR 50.62. Accordingly, the staff finds that the GGNS Unit 1 ARI design is in conformance with Paragraph (c)(3) of 10 CFR 50.62 and is therefore, acceptable.
1 The provision of Technical Specifications for the ARI system, including q
limiting conditions for operation and surveillance, is an acceptable method i
for demonstrating that the equipment satisfies the reliability requirements
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of the ATWS Rule. The BWR Owner's Group is working with the NRC staff to i
develop guidelines for a standard approach to ATWS-related changes to i
Technical Specifications. The licensee is a participant in this activity.
l The staff will provide guidance on a generic basis regarding Technical 1
Specifications for the ARI system.
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2.2 Standby liquid control system (SLCS) j s
The present GGNS Unit 1 SLCS is a two pump system.
Each pump is designed to inject 41.2 gpm. The present sodium pentaborate concentration is 13.0 weight percent. The proposed mode of operation to meet ATWS Rule requirements l
is for simultaneous two pump operation at a total flow rate of 82.4 gpm.
I This flow rate in conjunction with a minimum sodium pentaborate concentration l
of 13.6 weight percent is p(c) posed to satisfy the " equivalent control" ro requirements of paragraph (4) of 10 CFR 50.62.
The system description provided by the licensee has been reviewed by the staff against the requirements of the ATWS Rule (10 CFR 50.62), and Generic Letter 85-03, " Clarification of Equivalent Control Capacity for Standby Liquid Control Systems," dated January 28, 1985. The proposed mode of operation to achieve.a flow rate of 82.4 gpm with a sodium pentaborate minimum concentration of 13.6 weight percent is equivalent to 86 gpm at 13 weight percent and therefore is in compliance with 10 CFR 50.62. Accordingly, this proposed mode of operation is acceptable.
The licensee has also indicated that both SLCS pumps will be test-operated simultaneously to verify that the minimum allowable double pump flow rate of 82.4 gpm can be achieved. The licensee will submit proposed Technical Specifi-cations, including surveillance tests, for the simultaneous two pum) operating mode of the SLCS for staff approval prior to making this mode opera)1e.
2.3 ATWS recirculation pump trip (ATWS-RPT)
By letter dated April 3, 1987, the licensee stated that the Monticello ATWS-RPT reference design is used at GGNS Unit 1.
The GGNS Unit 1 ATWS-RPT which is presently operable is an energize-to-operate system with two-out-of-two low reactor water level or two-out-of-two high reactor pressure signals to trip the recirculating pumps. Each recirculating pump has two power supply breakers, one breaker for each trip logic division.
Either divisional initiation logic will trip the pumps. GGNS Unit 1 Technical Specifications 4.3.4.1.1 and 4.3.4.1.2 require periodic surveillance tests to demonstrate l
operability of each ATWS-RPT system instrumentation channel, l
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I As stated in the staff's SER on Topical Report NEDE-31096-P, the Monticello l
design is an acceptable reference ATWS-RPT design to comply with the ATWS l
Rule. Because the GGNS Unit 1 ATWS-RPT design used the Monticello reference I
design, the staff concludes that the GGNS Unit 1 ATWS-RPT design is in I
compliance with 10 CFR 50.62 paragraph (c)(5), and therefore is acceptable.
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3.0 CONCLUSION
l The proposed design of the GGNS Unit 1 ATWS-related systems references design l
concepts in the BWR Owners' Group Topical Report NEDE-31096-P " Anticipated j
Transients Without Scram; Response to NRC ATWS Rule 10 CFR 50.62." The staff's I
generic SER on NEDE-31096-P approved the design concepts and concluded that I
plants which reference the topical report and meet certain requirements stated
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in the SER will be found to be in compliance with 10 CFR 50.62.
Based on its review against the requirements in the staff's generic SER on NEDE-31096-P, the staff concludes that the proposed design of GGNS Unit 1 ATWS-related systems (alternate rod injection, standby liquid control system, and recirculation pump trip) meet the requirements in the generic SER. Accordingly, the staff concludes that the GGNS Unit 1 ATWS-related systems are in l
i compliance with 10 CFR 50.62 and are therefore acceptable, l
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