ML20151E374
| ML20151E374 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 07/15/1988 |
| From: | Gridley R TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| NUDOCS 8807260042 | |
| Download: ML20151E374 (10) | |
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TENNESSEE VALLEY AUTHORITY CH ATTANOOGA, TENNESSEE 37401 SN 157B Lookout Place JUL 151988 U.S. Nuclear Regulatory Commission ATTN:
Document Control Desk Washington, D.C.
20555 centlemen:
In the Matter of
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Docket Nos. 50-259 Tennessee Valley Authority
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50-260 50-296 BROWNS FERRY NUCLEAR PLANT (BFN) - ANTICIPATED TRANSIENTS WITHOUT SCRAM (ATWS)
RULE (10 CFR 50.62) - DETAILED PLANT SPECIFIC DESIGN The purpose of this letter is to provido the BFN ATWS detailed design criteria as requested in a letter from G. G. Zech to S. A. White dated April 13, 1988.
At a June 2, 1988 meeting in Rockville, Maryland, with the NRC staff, it was decided this could be accomplished by answering the checklist included in the letter to S. A. White from C. E. Gears dated January 8, 1987. Enclosuro 1 answers the checklist contained in the January 8, 1987 lotter.
This approach is acceptable since NRC understands the BFN ATWS design of the standby liquid control (SLC) and recirculation pump trip (RPT) from TVA letter to NitC dated March 1,1988, and the design review mooting on June 2,1988.
That letter and tr.eeting described TVA's intentions to use the enriched boron solution for the SLC design, the Monticello design for the RPT, whero the end-of-cycle breakers trip the recirculation pumps, and gave design information for the alternate rod injection (ARI) system.
The March 1, l'j88 letter referenced the Boiling Water Reactor Owner's Group (BWROG) Topical Report (NEDE-31096-P-A) for each aspect of the DFN ATWS design.
As a result of TVA's involvement in the F1 ROC, TVA understands NRC has expressed concerns pertaining to the diversity requirements between the analog trip unit (ATU) of the ARI system and the ATU of the reactor protection system. TVA's current design contains diversity between the ATUs of these systems and additional diversity (equipment and/or runufacturing) is not needed. Enclosure 2 presents TVA's reasons for this position.
8807260042 880715 0
DR ADOCK 05000D59 i
PNU l
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An Equal Opportunity Employer
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. U.S. Nuclear Regulatory Commission The BFH ATWS design conforms to the BWROC Topical Report and should be acceptable to NRC.
If you need further information, pleasn telephone M. J. May at. (205) 729-3570.
l Very truly yours, TENN 'SS E
.Y AUTHORITY a
.R.
'idley, Dlr clor Nuclear Licensing and Regulatory Affairs 1
Enclosures cc (Enclosures):
Hs. S. C. Black, Assistant Director for Projects l
TVA Projects Division U.S. Nuclear Re&ulatory Commission One White Flint, North 11555 Rockville Pike Rockville, Maryland 20852 Mr. F. R. McCoy, Assistant Director for Inspection Programs TVA Projects Divinion i
U.S. Nuclear Regulatory Commission Region 11 101 Marietta Street, NW, Suite 2900 Atlanta, Ceorgia 30323 Browns Ferry Resident Inspector l
Browns Ferry Nuclear Plant Route 12, Box 637 Athens, Alabaum 35611 i
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UROWNS FERRY NUCLEAR PLANT (BFN)
ANTICIPATED TRANSIENTS WITil0UT SCRAM DRTAILED DESIGN INFORMATION FOR Tile ALTERNATE ROD INJECTION 1
j DESIGN OBJECTIVE Alternato rod injection (ARI) is a part of the Anticipated Transients Without scram (ATWS) modification and is required by 10 CFR 50.62, "Requirements for Reduction of Risk from ATWS Events for Light-Wator-Coolod Nuclear Power Plants."
In the unlikely event that the normal method of reactor shutdown does not properly function, the ARI syrtem is designed as a backup system for the reactor protection system (Rps) in order to ensure safo coactor shutdown.
The BFN ARI system was designed to provide a path for safo reactor shutdown which is diverso and independent from the RPS.
Following an ARI initiation signal, the air supply to the hydraulic control units (HCU) is isolated and depressurized utilizing vont valves, thus allowing individual scram valvos to open. Opening of the individual scram valves will result in the control rods being inserted.
DESIGN BASIS The basic requirements for ARI design are specified in the HRC ATWS Rulo, 10 CFR 50.62, paragraph (c) (3), as shown in the following:
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Each boiling water reactor (BWR) must have an ARI system that is divorco j
from the reactor trip system from sensor output to tho actuation devico, b.
The ARI system must have redundant scram air heador oxhaust valves.
c.
The ARI system cust be designed to perform its function in a reliable mannor and be independent from tho existing reactor trip system from sensor output to the final actuation device.
The automatic signal to initiate the ARI comes from high reactor vossol pressure or low reactor vossol water level. The sotpoints for ARI inillation were chosen such that a normal scram should already havo occurred. The ARI function was also designed to minimize the possibility of inadvertent actuation. Detail design information is described in the following coction.
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Pl. ANT SPECIFIC REVIEW OF ARI SYSTEM On January 14, 1986, General Electric, on behalf of the UWR Owner's Group, published a licensing topical report NEDE-31096-p, "Anticipated Transient Without Scram; Responso to NRC ATWS Rule 10 CFR 50.62" which detailed conceptual designs to satisfy the 10 CFR 50.62 requirements for boiling water reactors.
NRC then issued a safety evaluation report (SER) dated October 21, 1986, to evaluato the acceptability of the proposed conceptual designs to moet the requirements of the ATWS rule. Based on the review, NRC concluded that the ARI design basis requirements stated in the topical report NEDE-31096-P in conjunction with the NRC staff requirements identlflod in the SER are in general coepliance with the ATWS rule 10 CFR 50.62 paragraph (c) (3).
To facilitato prompt revlows of plant specific ARI designs, the NRC staff has developed a checklist for the SER which itemized the ARI features approved by the staff. BFN has fully implemented an ARI design incorporating those features covered in the checklist in order to be in conformance with the ATWS Rule 10 CFR 50.62 paragraph (c) (3) on ARI requirements.
Each item it. the chocklist is described in the following section for BFN design. The checklist shown as appendix A in the NRC SER, rather than the items in the SER main body, was used for this report por NRC/TVA mooting on June 2, 1988.
Item 1.
ARI Syntem Function Timo Rod injection motion will begin within 15 seconds and be comploted within 25 seconds from ARI initiation.
DFN Dosinn According to the BWR Owner's Group Report, NEDE-31096-p, rod insortion should be defined on a plant-specific rod scram motion times.
Section 3.2 of the report states that the ARI design objectivo can be mot provided full rod insertion occurs within approximately 60 seconds of the ARI I
initiation signal.
The UFN ARI system, however, is designed to achievo the 15-to 25-second rod insertion motion perforrtanco.
In order to moet this critorion, it is neccesary for UFN to deproscurlzo the scram air heador as fast as i
possible. Therefore, several vont valvou as well as block / vent valvoc J
are installed on the air supply headers for the control rod delvo (CRD)
HCUs.
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T A study of the scram air header depressurization characteristles was l
perforged in order to verify that the BFN A'RI design meets tho system i
function timo requiremont.
A computer program was developed to calculato the air venting timo.
The venting timo calculation ovaluates two casost (1) Operation of all eight ARI valvos (including two AR1 block valvos), and (2) Opochtion of only one 4
channel of four ARI valves.
The eight valvo configuratlon is the ARI design approach which is used in rest BWR plants.
The result of the analysis indicatos that the air pressuro in the HCU scram i
diaphragm valves will depressurizo from the initial prossero of 70-15 psig to 23 pain in 11 sceonds. The scram inlet and outlet valvos will begin to open 4
when the pressuro is reduced to approximately 30 pais. Since the CRD fluid, water, is incompressible, beginning of the scram valvo moving timo equates the start of CRD motion.
For the scenario of four ARI valvo operations, only one valvo in each pair was designed to be onorgized to maint ain the same venting locations for each HC9 bank and ucram dischargo volumo (SDV). The venting timo calculation for four valvo operation is for a failuro scenario in one logle channel and is for a conservativo caso.
Since it is nocessary from ARI design to install at least a vent valve for each HCU bank, a vont valvo for SDVs and a block valvo, the four valvo operation is the minimum requirement for UFN ARI design for one electrical channel. The depressurization time is slightly moro (loss tiwn 1/4 second) than the eight valvo caso and thus also moots the ARI timo requirement.
In summary, assuming that the timo from ARI initiation (from the reactor sensors) to energization of AR1 vont valvos is loss than 1 second, tho
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control rod motion will begin less than 15 seconds af' ce ARI initiation.
BFNP control rods will be fully inserted well within ton seconds af ter tho motion has begun and the ARI will be completed within the 25-socond timo i
requirement from ARI initiation.
The operating time of the ARI vont and block valvos is 0.25 seconds maximum and is negligible compared to the total required time of 15 seconds for the rod insortion motion to begin.
Item 2.
Safety-Related Requirements (a) Class IE isolators are used to interface with safety-related systems.
(b) Class IE isolators are poworod from a Class IE sourco.
(c) Isolator Qualification documents are availablo for staf f audit.
BFH Denlan (a) & (b) Whenever the ATW3 (AR1/RPT) intarfacco with the IE components and systems, proper isolatica dovleco are provided. The two instances where isolation was required and provided are:
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(1)
Emergsney core cooling systens (ECCS) cabinots whoro an isolation rolay in provided betwcon the trip output relays of the pressuro ated ^.uvol transmittoew and ARI/RPT systens.
(2) Two fuses in series woro used as propor isolators betwoon tho Class 1E ?SOV DC supply and tha AR1/RPT systems as required in section 6.2, item 9 of the NRC SER.
t (c) The isolation relays aro quallflod a.1 such and qualification reports will be available for staff audit.
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Item 3.
Redundag,cy c
The ARI system performs a function redundant to tho bm;kup sceau system.
B7N Design The function of the BFN ARI system is fully rodundant tc the existing backup scram system which utilizes the identical reactor ceram method..
Following an ARI initintion signal, the air supply to the scram valvos will bo isolated and the scram air header will bo vented to reduco air pressure in the headot, shus allowing individual scram valvoc to open.'
The control rod delvo units then insert F.he control rods to shut 'down the reactor.
Item 4.
Diversity of Exteting RTS (a) ARI syntem is energizo-to-function.
(h)
/.R1 system uses DC poworod valves.
(c) Instrument channel components (excluding sensors but including all j
signal conditioning and isolatloa devices) are diverso from the exist.ing
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RTS cor.posents, j
BFN Design
- Lt ' 'TWS (AR1/RPT) system as required by the 10 CFR 50.62 rulo must bc cot,.totely separato from the RPS.
This provision has been provided in the design.
(a) Devicoc in the ARI/RPT systems sto normally do-onorgized and will energ*.ze to function.
(b) The ATWS ARI/RPI systeme tro supplied by 250V DC power.
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(c) Signal conditioning devices and isolation devices are diverso for RPS.
The instrument loops that have boon utilized for AR1/RPT inlliation have boon selected such that any a iverso interaction with any other instrumentation is avolded.
The analog trip units have been located in panels that are not utllized for any recctor trip functions.
Applicablo circuits and raceways havo either been added o. modified to bo indopondent of the RPS.
Item S.
Electrical Independence from the Existing RTS (a) ARI actuator logic separate fron. LTS logic.
1 (b) ARI circuits are isolated from safoty-related circulte.
BFN DesiRn (a) The ATWS (ARI/RPT) system has its own actuation logic circuit. The circuit receives its signal from the ARI analog telp units.
1 (b) Wherever the ATWS (ARI/RPT) circuits come into contact with Class 1R safety-related circuits, proper isolation is provided.
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Item 6.
Physical Separation fj;om the Existing PTS (a) ARI system is physically separated from RTS.
BFN System Physical separation is maintained betwcon the RPS and ATWS (ARI/RPT) from the transmitters to the final trip devices.
Item 7.
Environmental Qualificat!on ARI equipment in qualified to conditions during an ATWS' ovent up to the Limo the ARI function is completed.
UFN Design The AR1/RPT systems are not required to be safoty-related based on the NRC SER.
Mechanical portions of the ARI/RPT modific&tions are nonsafety-related.
Isolation of nonsafety-rotated electrical ihstruments from the safoty-colated equipment _lu achieved by using quallflod isolation devices (relays and fuses). Equipment required for the ARI/RPT to function proporly aro qualified to the conditions during an ATWS ovent up to the time that the ARI/RPT function is completed in accordance with the NRC SER.
Item 8.
Quality Assucanco (a) Comply with Conceic Lotter 85-06 BFN Design The ATWS Rulo does not require the AR1 system to be safety-related and implementation of the ATWS system nood not moot all aspects of 10 CFR 50 App 9ndix B, quality assuranco requirements. NRC has recognized that existing industry practices applied to nonsafety-related equipment are acceptable for specific application for nonsafety-related ATWS equipment. This pasition is explicitly stated in NRC Generic Lottor 85-06.
Therefore, the organization and program, design control, procurement, installation, inspection, testing, maintenanco, modification and other related works are in accordance with the guidance in the Concric Letter 85-06 for AR1/RPT systems.
The UFN ATWS Quality Assurance program requirements are contained in the Nuclear Quality Assurance Manual Part 1, Section 1.3.
Items 9.
Safety-Related Power Supply (a) ARI system power independent from RTS.
(b) AR1 system can perform its function during any loss-of-offsito power event.
3 BFN Dosinn (a) The ATWS (ARI/2pT) system is supplied by. tass IE power from the 250V rc Shutdown Board batteries. The RpS is supplied by power from the battery boards.
(b) In the event of a loss-of-of fsito power, power is supplied by the shutdown board batterlos.
Item 10.
Testability at Power (a? ARI testablo at power.
.l (b) Bypass features conform to bypass criterla used in RTS.
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~7-ocN Design The ATWS ( ARI/RPT) design conforms with the requiremont that the system be testable at power. Tha use of'two lovel transmitters and two pressure transmitters ett a 2-out-of-2 logic, and the presenco of two AR1/RPT initiation channels potMit tho testing of ono channel while the other is still operable. It also permits the testing of one trip-unit without initiating ATWS (AR1/RPT) since two trip units must'operato at once to initiato AR1/RPT.
Itom 11.
Inadvertent Actuation (a) ARI actuation sotpoints will not challengo scram.
(b) coincidence logic is utilized in AR1 design.
BFN Design (a) The setpoints for the AR1/RPI initiation are such that the normal scram from the RPS will tako placo prior to any AR1/RPT initiation. This has boon accomplished by developing sotpoint values f or the ALL/RPT initiation that have a lower trip sotting for the reactor vessel low level and a highor trip sotting for the reactor vessel high pressure than.those of the existing RPS normal scram trip settings.
(b) Two coincident signals of low reactor water lovel or high reactor pressuro will inillato AR1/RPT. A single failure of a levol sensor or pressure sensor will not initiato an ARI or precludo ARI/RPT operation..This is accomplished by placing two contacts ir, series to ensure that only coincident signals will send out a trip signal to initiate ARI/RPT.
Item 12 Manual Initiation (a) Manual initiation capability is provided.
BFN Design Manual initiation of ARI has boon provided in tho form of hand switches that can allow activation of wanual ARI in tho main control room utilizing hand switches. Manual initiotton of AR1 has boon designed to ensure that trip outputs to the recirculation pump motor-generator sota are blocked out to ensure that the recirculation pump trip will not tako
-i place during manual initiation of ARI.
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. 0 Item 13. Information Roadout (a) Information roodout is provided in main control room.
BFH Dosinn Four annunciation windows are provided in the control room for ATWS (ARI/RPT).
(1) One window to indicato auto initiation of both ARI and RPT with input from two channels in parallol.
(2) One window to indicato ARI manual initiation with input from the two channels in parallol.
(3) One window to indicato t'nat Channel A is under test.
(4) One window to indicato that Channel B is under test.
Item 14.
Complotlon of Protectlvo Action Onco It Is Initiated BFH Design The ARI/RPT circuits are provided with a resot switch in the main control room and at the local ATWS panols. However, tho circuits are
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provided with a seal-in feature that provents the rosetting of the circuit for the first 30 seconds af ter the automatic initiation of ARI/RPT or the manual initiation of ARI.
The 30 second delay is provided to encure that the rods have boon fully inserted before the circuit can be roset, provided the initiation signals havo boon cleared.
ENCLOSURE 2 0
BROWNS FERRY NUCLEAR PLANT ANTICIPATED TRANSIENTS WITil0UT SCRAM POSITION ON 10 CFR 50.62 DIVERSITY REQUIREMENTS FOR ALTERNATE ROD' INJECTION From industry contacts, TVA has learned that NRC does not think the present diversity contained in most Anticipated Transients Without Scram (ATWS) designs is adequato.
Specifically, TVA understands that NRC will require equipment and/or manufacturing diversity betwoon the analog trip unit ( ATU) of the reactor protection system (RPS) and the ATU of the ATWS alternato rod injection (ARI) system.
10 CFR 50.62(c)(3) states "Each bolling water reacto" must have an ARI system that is diverso (from the reactor trip systems from sensor output to the final actuation devico."
- ho Browns Ferry Nuclear Plant (UPN) ATWS design maintains diversity betwoon tho ATU of the HPS and the ATU of the ARI system and meets the 10 CFR 50.62 requirement for the following reasons:
(1) RPS is de-onorgized to function; ARI is oncegized to function.
(2) RPS is AC powered; ARI is DC poworod.
(3) RPS is ono-out-of-two taken twico logic; ARI is two-out-of-two ic3 c.
1 (4) The RPS is completely independent.and separato from the ARI.
(5) On scram signals, the HPS acts on the scram pilot solenoid valves to relievo air on the scram valvos of each hydraulic control unit; on signals dif ferent from the RPS scram signals, the AR1 acts on its own separato vont valvos to depressurize the scram air heador to relieve air on the scram valves.
(6) An ATU in the RPS is used in a reactor trip on low reactor-water lovel and high reactor pronsure trips; however, there are numerous other reactor trips that do not use an ATU.
The Statomonts of Consideration defines the ATWS diversity requiremont by stating "Equipment diversity to tho extent reasonablo and practical to minimize the potential for common cause failuro is required..." TVA considers the current BFN design to bo diverso "to tho extent reasotoblo and practical" for the following reasons:
(1) The ATUs that are prosently availablo to the industry are similar in design. TVA uses the ATU which was determined to havo the best design.
To install a different ATU could potentially decrease the system's cellability.
(2) From the roanalysis of the BFN Probabilistic Risk Ausossment, ATWS does not have a significant offect on the coro damago frequency. Thoroforo, if manufacturing and/or equipment diversity climinated all common cause uncertainty, which it would not, the coro damage frequency would bo only very slightly improved.
(3) TVA estimatos that the cost of providing this additional diversity would cost over $500,000 por unit for tho design, procurement, and installation. It is also estimated this additional offort would tako sevocal tnonths to implomont.
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.-Since the ARI ATO and the RPS ATU are already diverse "to the extent-reasonable and practical," TVA considers ttfe NRC requiremont of additional' diversity to be counter productive and would add no safety benefit.
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