ML18031B297
| ML18031B297 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 04/22/1987 |
| From: | Gridley R TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| GL-85-06, GL-85-6, NUDOCS 8704280260 | |
| Download: ML18031B297 (9) | |
Text
REGULATORY I ORNATION DISTRIBUTION.BYS (RIDS>
ACCESSION NBR: 8704280260 DOC. DATE: 87/04/22 NOTARIZED:
NO FAG IL:50-259 Brogans Ferv
<l Nuc 1eav Poucr 8+ation>
Unit f >
Tennessee 50-260 Brogans Ferry Nucleav'ouer S+ation>
Unit 2>
Tennessee 50-296 Brogans Ferv g Nucleav'ouer Station>
Unit 3>
Tennessee AUTH. NANE AUTHOR AFFILIATION GRIDLEY> R.
Tennessee Valley Authority RECIP. NANE RECIPIENT AFFILIATION Document Contv ol Branch (Document Contv ol Desk)
SUBJECT:
Forwards info v'e pv'oposed me+hods of compliance w/*TWS Rul fOCFR50. 62 plant specific design> pev'E Gears 870i08 1+r 8702f8 telcon. NRC concuv rence v equested pv ior to imp 1 ementati on.
DISTRISUTION CODE:
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TITLE: OR/Licensing Submittal:
Salem ATWS Events GL-83=28 NOTES: Zvolinslli 5 cg. i cg ea to:
Axelrad> Ebneter> S. Richav'dson>
Liatu> Q. Zech> OI> OIA.
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Lia~> Q. Zech. OI. OIA.
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Liam G. Zech OI, OIA.
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TENNESSEE VALLEYAUTHORITY CHATTANOOGA, TENNESSEE 37401 5N 157 Lookout'lace.
U.S. Nuclear Regulatory Commission ATTN:
Document Control Desk Washington, D.C.
20555 P,PR gg l98T 1
r Gentlemen:
In the Matter of Tennessee Valley Authority Docket Nos. 50-259 50-260 50-296 BROWNS FERRY NUCLEAR PLANT (BFN) ANTICIPATED TRANSIENTS WITHOUT SCRAM (ATWS)
RULE (10 CFR 50.62)
PLANT SPECIFIC DESIGN In response to a letter from G. E. Gears to S. A. White dated January 8, 1987, we are providing information regarding proposed methods of compliance with the ATWS rule.
As discussed with Mr. Gears during a telephone call on February 18, 1987, the enclosed is conceptual information to be used for preimplementation review.
Detailed design information, which is not yet available, will also be provided for postimplementation review after the design is complete.
In a letter from R. H. Shell to H. R. Denton dated October 11,
- 1985, TVA submitted to NRC a brief description and schedule for implementation of ATWS rule requirements.
NRC indicated concurrence with this information in a letter from R. J. Clark to S. A. White dated March 31, 1986.
Proposed plant modifications for ATWS compliance are in accordance with that information, except that the schedule for implementation has been accelerated to include the modifications in BFN's current unit 2 cycle 5 refueling, outage.
TVA is a member of the Boiling Water Reactor Owners Group ATWS Committee and certain portions of NEDE-31096-P are referenced in the enclosure.
- However, some unique features of the proposed BFN design are not specifically addressed in the report.
Therefore, TVA requests NRC concurrence with the concept before implementation.
If you need further information, please refer any questions to J. L. Turner, Site Licensing, Browns Ferry, (205) 729-2853.
8704280260 870422 PDR ADOCK 05000259 P
PDR Very truly yours, TENNESSEE VALLEY AUTHORITY Gridley, Director Nuclear Safety and Licensing Enclosure cc:
On page 2
An Equal Opportunity Employer
U.S. Nuclear Regulatory Commission APR RR 1987 cc (Enclosure):
Mr. G.
G. Zech, Assistant Director Regional Inspections Division of TVA Projects Office of Special Projects U.S. Nuclear Regulatory Commission Region II 101 Marietta St.,
NW, Suite 2900 Atlanta, Georgia 30323 Browns Ferry Resident Inspector Browns Ferry Nuclear Plant Route 2, P.O.
Box 311
- Athens, Alabama 35611
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ENCLOSURE ANTICIPATED TRANSIENTS WITHOUT SCRAM (ATWS)
CONCEPTUAL DESIGN INFORMATION BROWNS FERRY NUCLEAR PLANT (BFN)
Introduction This enclosure will define BFN's conceptual design for meeting the requirements of the 10 CFR 50.62 ATWS rule.
The design objective for the standby liquid control (SLC), alternate rod injection (ARI), and recirculation pump trip (RPT) will be discussed.
Where applicable, credit is taken for the Boiling Water Reactor Owners Group (BWROG) Topical Report (NEDE-31096-P).
This information is intended for use in preimplementation review with final review to occur after the work is complete.
Standb Li uid Control TVA has chosen to use an enriched boron solution to meet paragraph C(4) of 10 CFR 50.62.
Implementation will be in accordance with section 2.2.3 of NEDE-31096-P.
Alternate Rod In 'ection In the unlikely event that the normal method of reactor shutdown does:..not properly function, the BFN ARI design for the ATWS rule is to be a backup for the reactor trip system (RTS) in order to ensure reactor shutdown.
Modifications will be made to meet paragraph (C)(3) of 10 CFR 50.62.
ARI Desi n Ob'ective:
The ARI system, which will include the existing backup scram valves, provides a path to reactor shutdown which is independent of the normal reactor shutdown method.
The ARI system uses signals received from pressure and level transmitters which are electrically independent of the reactor protection system (RPS) to indicate an ATWS event has occurred.
These sensors will provide a trip signal upon reactor vessel low water level or reactor vessel high pressure and are associated with the emergency core cooling system (ECCS) which use energize-to-trip logic signals.
The setpoints chosen for the ARI initiation signals are such that a normal scram should already have occurred.
Signals are sent through relay logic to energize the existing backup scram valves.
The control rods are required to be fully inserted within approximately 60 seconds.
Testing at BFN indicates that the scram air header can be depressurized using the backup scram valves resulting in complete rod insertion within the 60-second requirement.
This meets the requirements of NEDE-31096-P, section 3.2.
Safet -Related Re uirements:
The ARI system will be designed such that it. is electrically isolated from safety-related systems.
Isolation methods will be in accordance with the licensing basis requirements for BFN.
Generally, qualified fuses and relay coil-to-contact separation are used.
In accordance with NEDE-31096-P, the ARI system itself will not be safety related.
ATWS CONCEPTUAL DESIGN INFORMATION (Cont'd) valves; that is, they will perform their function given the failure of a single exhaust valve. It will also be redundant to the individual scram pilot valves which normally initiate a scram.
TVA differs with the position stated in Table A-1 of NEDE-31096-P that the ARI performs a function redundant to the backup scram function.
The function of the backup scram is to complete control rod insertion in the event that there is a failure of one or more individual scram pilot valves.
Because the backup scram function depends upon the same logic and sensors as the normal scram
- valves, the failure of one or more individual scram pilot valves is the only situation in which the backup scram function would have an effect upon control rod insertion.
In contrast, the function of ARI is to shut down the reactor in the event of failure of the RTS.
Therefore, the ARI performs a function different than the backup scram and not redundant to it.
TVA's understanding of the ARI design basis is that. it is to be redundant to the RTS.
In this case, the RTS is the portion of the system which causes the control rods to insert during a scram.
This requires operation of the individual scram pilot valves.
The backup scram function is considered outside of the RTS because it is not needed and no credit is taken foe it in the initiation of a scram.
The intent of the ATWS rule is that the ARI have scram air header exhaust valves that are redundant to the individual scram pilot valves.
The proposed ARI design meets this requirement by using the existing, backup scram valves which are redundant to and independent from the individual scram pilot valves.
Diversit From Existin Reactor Tri S stem:
The ARI and RPT use common sensors and initiation logic.
The ARI/RPT receives reactor vessel low water level (-51.5 inches) or reactor vessel high pressure (1120 psig) signals from transmitters that are electrically independent from the RPT.
The normal RPS reactor vessel low water level and reactor vessel high pressure scram setpoints are +11 inches and 1055 psig respectively.
The backup scram valves and the ARI/RPT use dc power, instead of ac power used by RPS, which will enable it to function with a complete loss of offsite power.
The trip logic is contained in the ECCS cabinets which provides diversity from the RPS.
The ARI system uses an energize-to-trip logic signal to actuate the backup scram
- valves, compared to the deenergize-to-trip logic of the RPS to operate the individual scram'ilot valves.
The proposed design is in accordance with NEDE-31096-P regarding diversity from the existing RTS.
Electrical Inde endence from the Existin Reactor Tri S stem:
The ARE system will be electrically independent from the RTS.
The ARI is connected electrically to the backup scram portion of the RPS which is itself an existing system that is electrically isolated from the RTS.
This arrangement will meet the requirements for electrical independence.
The proposed design is in accordance with NEDE-31096-P except for the distinction between RPS and RTS noted above.
ATWS CONCEPTUAL DESIGN INFORMATION (Cont'd)
Ph sical Se aration from the Existin Reactor Tri S stem:
The sensors and logic components which provide ARI/RPT trips are physically separated from the'PS.
The control circuitry for ARI initiation closes contacts to actuate the backup scram valves which are separate from the contacts already used by RPS.
Isolation devices are used to prevent any fault in the ARI from disabling the RPS function of the backup scram valves or any other RPS function.
The physical separation of the proposed ARI design is in accordance with section 3.3.10 of NEDE-31096-P.
Environmental alification:
The ARI/RPT system is required to function for anticipated operational occurrences but not. for design basis accidents (loss of coolant accident and high-energy line break).
All hardware required for the ARI to function properly will be environmentally qualified to conditions during, an ATWS event up to the time that the ARI function is completed in accordance with section 3.3.7 of NEDE-31096-P.
ualit Assurance:
Since 10 CFR 50.62 does not require ATWS equipment to be safety related, implementation of the ATWS system requirements at BFN need not meet all aspects of 10 CFR 50, Appendix B, quality assurance requirements.
NRC has recognized that existing industry practices applied to nonsafety-related equipment are acceptable for specific application ta ATWS equipment.
This position is explicitly stated in NRC Generic Letter 85-06.
Therefore, the design, installation, preoperational phase testing, and future maintenance or modification of the BFN ATWS equipment will be in accordance with nonsafety-related 'quality assurance practices.
This is consistent with the intent of Generic Letter 85-06.
Safet -Related 1E Power Su l The ARI/RPT logic as well as the power to the backup scram valves use 250V dc power.
This power will be available if offsite power is lost and is independent of the RPS
~
This same power source is used for motive power for some ECCS components.
For this reason, proper isolation will be used for separation between the ARI and a safety-related power supply where applicable.
Testabilit at Power:
TVA has chosen to implement two-out-of-two logic providing an energize-to-trip logic signal opening the existing backup scram valves upon reactor vessel low water level or reactor vessel high pressure.
With this arrangement, each signal and its associated instrumentation can be tested during plant operation without inadvertent actuation.
This meets the requirements of section 3.3.9 of NEDE-31096-P.
Inadvertent Actuation:
Normal reactor scram should already have occurred at the time the ARI reaches its initiation setpoints.
The ARI initiation logic will use coincident logic to minimize the likelihood of inadvertent actuation.
This design supports generic industry efforts to reduce unnecessary scrams; This meets the requirements of section 3.3.2 and 3.3.11 of NEDE-31096-P.
ATWS CONCEPTUAL DESIGN INFORMATION (Cont'd)
Additional Features in the Desi n:
The ARI system will have the capability of being manually initiated from the control room.
Once the ARI has been initiated, the operations personnel in the control room will have information available that indicates.initiation of the ARI, ARI function in progress, and ARI function completed.
Once the ARI is initiated, both the automatic and manual actuation signals will seal-in to ensure that all control rods have had adequate time to fully insert.
Reset of the ARI will be prohibited for the duration of the seal-in time but afterward can be manually reset if the automatic initiation signals have cleared.
The ARI uses two-out-of-two logic.
Due to the two-out-of-two logic, any circuit up to the final actuation device may be tested or replaced without a bypass switch.
This logic can be used for testing, calibration, or maintenance by tripping one part of the logic since it takes both parts of the logic for ARI/RPT initiation.
The above additional features are in accordance with NEDE-31096-P.
Recirculation Pun Tri RPT The proposed RPT design to meet paragraph (C)(5) of 10 CFR 50.62 will use the same input sensors and two-out-of-two logic as the proposed ARI.
The RPT initiation will trip the normal and emergency feeder breakers to the drive motors of both recirculation pump motor-generator sets.
This design is similar to the Monticello design in NEDE-31096-P except that'the BFN RPT trips the feeder breaker as in the original BWR/4 design.
The Monticello design trips the field breaker.
Modifications to the existing RPT will be made in conjunction with the ARI modifications in order to have the RPT initiate from the same two-out-of-two logic as the ARI.
This modification will reduce the probability of inadvertent tripping of the recirculation pumps.
r Consistent with the position given in NEDE-31096-P and 10 CFR 50.62, the design does not utilize redundant trip coils.
The RPT system is as reliable in its ability to trip the recirculation pump as called for in NEDE-31096-P.
Addition of redundant trip coils would increase system reliability only slightly because the remainder of the logic to trip the pumps is not redundant and is susceptible to single failure of the other components.
TVA is working with the BWROG to resolve this issue generically.