ML19264B199
| ML19264B199 | |
| Person / Time | |
|---|---|
| Site: | 05000000, Sequoyah |
| Issue date: | 07/10/1980 |
| From: | Check P Office of Nuclear Reactor Regulation |
| To: | Tedesco R Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML093450149 | List:
|
| References | |
| FOIA-80-515, FOIA-80-555 NUDOCS 8007290653 | |
| Download: ML19264B199 (16) | |
Text
.L JUL 10 1980 DISTRIBUTION:
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ASB READIiiG PCHECK J. '
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Docket Nos: 50-327/328 FOiORANDUM FOR: Robert L. Tedesco, Assistant Director for Licensing, DL FROM:
Paul S. Check, Assistant Director i
for Blast Systems, DSI l
E9DaECT:
SEQUOYAH UNITS 1 & 2 - SAFETY EVALUATION REPORT INPUT ON THE IMPLEMENTATION OF REC 0FfiENDATIONS FOR THE AUXILIARY EZ5? WATER SYSTEM j
1 l
The Auxiliary Fystems Branch has completed its review of the Auxiliary Feed-i water System reliability for the Sequoyah facility. In a letter dated
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March 10. 1900, our requirements regarding the Sequoyah Auxiliary Feedwater System were fomarded to the Tennessee Valley Authority (TVA). TVI pro-j vided responses in letters dated January 25,1980, April 15.1980, and May 1, 1980.
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We have completed our review of TVA's responses and have prepared a Safety Evaluation Report (SER) input which is atatahed. The SER contains two items for which our review is not complete. Both of these matters are dated items -
licensee implementation is required by January 1981:
1.
Reconnendation (Item 2.1.7.b of NUREG-0578) - The licensee's response will be reviewed and our evaluation will be presented in a supplement to this SER.
2.
Reconnendation GL The licensee's response will be reviewed and our evaluation will be presented in a supplement to this SER.
ongmat si,;:ca dz Paul s. check Paul S. Check, Assistant Director for Plant Systems Division of Systems Integration Attacnment:
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SAFETY E'/ALUATION REPORT SEQUOYAH STATION, UNITS 1 & 2 DiPLEMENTATIONS OF RECOMMENCATICNS FCR AUXILIARY FEECWATER SYSTC15 I.
Introduction and Sackorcund The Three Mile Island Unit 2 (TMI-2) accident and si secuent investigations and studies highlighted the importance of the Auxiliary Feedwater System (AFJS) in the mitigation of transients and accidents. As part of our assessment of tne TMI-2 accident and related implications for ocerating c'. ants, we evaluated the AFW systems for all operating plants having nuclear steam supply systems (NSSS) designed by 'Jestinghouse (NUREG-0611) or Combustion Engineering (NUREG-0635). Our evaluations of tnese system designs are contained in the NUREGs along with our recomendations for each plant and the concerns which led to each recommendation. The objectives of the evaluation were to:
(1) identify neces-sary changes in AFd system design or related procedures at the operating facili-ties in order to assure the continued safe operation of these plants, and (2) to identify other system characteristics of the AFA systems which, on a long term basis, may recuire system modifications. To accomplish these objectives, we:
(1) Reviewed plant specific AF4 system desiens in light of current regulatory requirements (SRP) and, (2) Assessed the relative reliability of the various AFW systems ander va-ious loss of feedwater transients (one of which was the initiating event of TM!-2) and other postulated failure c:nditicns by detemining t' e ootential r
. for AFW system failure due to common causes, single point vulnerabilities, and human error.
We concluded that the implementation of the recommendations identified during this review will considerably improve the reliability of the AFW systems for each operating plant.
The following plant specific recommendations did not apply to this plant:
GS-8 and GL-1.
The basis for these recommendations can be found i'. Appendix III of NUREG-0611 and tne system description which determined the basis for not applying these recommendations can be found in Section X of NUREG-0611.
II.
Imolementation of Our Recommendations A.
Short Term Recommendations 1.
Recommendation GS The licensee should propose modifications to the Technical Specifications to limit the time that one APA system pump and its associated flow train and essential instrumentation can be inoperable. The outage time limit and subsequent action time should be as required in current Technical Specifications; i.e., 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> and 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />, respectively.
In response, the licensee indicated in a letter dated January 25, 1980, that the existing Seoucyah Technical Specification, section 3.7.1.2 applies. This Specification limits the plant operation with one AFW train our of service to 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> and the subsecuent action time to 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. We conclude that this Technical Specification is in com-pliance with our reccmmendation and is, therefore, acceptable.
. 2.
Recommendation GS The licensee should lock open single valves or multiple valves in series in the AFW system pump suction pioing and lock open other single valves or multiple valves in series that could interrupt all AFW flow. Monthly inspections should be performed to verify that these valves a.re locked and in the open position. These inspections should be proposed for incorporation into the surveillance requirements of the plant Technical Specifications. The long term resolution of this concern is discussed in Recommendation GL-2.
In response to this recommendation, the licensee indicated in a letter dated January 25, 1980, that there is nc single valve or multiple valves in series in the AFW system pump suction piping and single valves or multiple valves in series that can defeat the system.
Alternate water sources to the pump suctions do not share the same flow path with any valves in the normal water supply lines.
In addi-tion, the AFWS suction will automatically align to an alternate water source (essential raw cooling water) on low suction pressure in each AFW pump. We have reviewed the licensee's response and conclude that the existing design meets this recommendation and is, therefore, acceptable.
3.
Recommenda:icn 35 The licensee has sta:ed tnat i t throtties AFW system flow to avoid water hammer. The licensee was recuested to reexamine the practice of throttling AFW system flow to avoid water nan?,e r.
4 The licensee should verify that the AF4 system will supply on demand sufficient initial flow to the necessary steam generators to assure adequate decay heat removal fol! awing loss of main feedwater ficw and a reactor trip from 100% pcwer.
In cases where this reevaluation results in an increase in initial AFJ system flow. the licensee should provide sufficient informaticn to demonstrate that the recuired initial AFJ system ficw will not result in plant damage due to.va:er namer.
In response to this recommendation, the licensee in a letter dated January 25, 1980, indicated that on automatic start the AFd system will deliver full flow until nor al water level is established in the steam generators. AFJ flow will not be prevented or reduced due to water hammer. The steam generator feedwater rinq headers in Sequoyah have been modified to minimi:e the possibili+v of a water hamner.
'de requested the liceriaee to provide a response to our request in of our letter dated fiarch 10, 1980, regarding the design basis for AFJS flow requirements. The licensee provided this infoma-tion in a letter dated January 25, 1980. Ele have reviewed the licensee's asnnnte and have concluded that its design basis for AFdS flow require-mants are acceptable.
. 4
- ec:nmenoatien 35 Emergency crecedures for transferring to alter-nate sources of AF4 supply should be available to the olant operators.
These procedures should include criteria to inform the acerator when, and in what order, the transfer to alternate water sources should take place.
The following cases should be covered by the procedures:
- Primary water supply is not initially available. The procedures should include any operator actions required to protect the AFA system pumos against self-damage before water ficw is initiated;
- and,
- Primary water supply is being depleted. The procedure should or0 vide for transfer to the alternate water sources prior to draining of the primary water supoly.
In resconse to this recommencation, tne licensee indicatec in a letter cated January 25, 1980, tnat each AFA pumo has its own safety grade instrumentation that will sense low pump suction pressure prior to draining of the normal water source and will automatically align tha safety grade backup water source to the pump. Isolation from the normal water source also occurs automatically by '.losure of a check valve in each nurn secti.cr. lina due to bac!: r:ssura in the valve upon alignment of the qualified water source. The qualified 'va:er source is the essential raw :coling water. We conclude that the above autcmatic features of the licensee's design adecuately address this recommendation and that additional procedures are not recuired.
. 5.
Recc. endation 35 The as-b. :: plan should be ca able of croviding the required AF4 flow for at least r.vo hours from one AF4 pump train, independent of any alternating current pcwer source.
If manual AF4 sys-tem initiation or ficw control is required folicwing a comolete less of alternating current gewer, emergency procedures should be established for manually initiating and controlling the systen under tnere canditions.
Mnce the water for cooling of the luce oil for the turoine-driven pump tearings may be dependent 01 al ternating current pcwer, design or proce-ducal changes snall :e made c al'+ ate this decendency as scen as practicable. Until this is dene, the emergency procedures should pro-vide for an individual to be stationed at the turbine-driven pump in the event of the loss of all alternating current pcwer to monitor pumo bearing and/or lube oil temperatures.
If necessary, this operator would operate the turbine-driven pump in a manual on-off mode until alter-nating current pcwer is restored. Adecuate lighting powered by direct current pcwer sources and communications at local stations should also be provided if manual initiation and control of the AF4 system is needed.
(See Recomendation GL-3 for the longer-term resolution of this concern.)
In response to this recommendation, the licensee indicated in a letter dated January 25, 1980, that the turbine-driven pump can run for two hours using only battery power for control and a battery powered room fan to remove heat from the pump room.
. The licensee furtner indicateo tnat emergency procedures have been established to cover the event of loss of all AC power sources. We conclude that the provisions available in the existing AFi system in Sequoyah meets the requirements outlined in this recommendation and is, therefore, acceptable.
6.
Recomendation GS The licensee should confim flow ::ath availability of an AF4 system flow train that has been out of service to perfom periodic testing or mair.tenance as followr:
- Procedures should be implemented to recuire an operator to detemine that the AF4 system valves are procerly aligned and a second operator to independently verify that the valves are properly aligned.
- The licensee should propose Technical Scecifications to assure that prior to plant startup following an extenced cold shutdown, a flow test would be perfomed to verify the normal ficw path from the primary AF4 system water source to the steam generators.
The flow test should be conducted with AF4 system valves in their nomal alignment.
In a letter dated January 25, 1980 the licensee stated that procedures are in place which require the operation to determining if AF4 system valves are properly aligned when perfoming technical specification surveillance (testing or maintenance) and when performing any maintenance. While the licensee does not require a second operator to directly verify AFA valve alignment, the technical specifications require that AF4 valve alignment be verified every seven days.
Additionally, Sequoyah has a status monitoring system with control board
. indication lights. The status monitoring system automatically checks AFW valve alignment and alarms if the alignment is not connect.
The licensee requires an AFW flow test to be performed with the AF4 system valves in normal alignment for emergency operation.
During any startup, until steam generators are filled, the AFA motor driven pumps are used to supply water from the condensate storage tank to the four steam generators.
The AFA automatic level control system is used to maintain steam generator level until the plant is at a power level (approximately 5". power) sufficient to transfer to the main fuel pumps.
During AFA supply to each steam generators, ARl flow and steam generator level must be monitored for the assessment that adequate flow criteria have been met for each steam generator and for the performance of each APW motor driven pump. 'Je have reviewed the licensee's response and conclude that it meets the requirements of this recommendation and is, therefore, acceptable, 7.
Recommendation GS The licensee should verify that the automatic start AF4 system signals and associated circuitry are safety-grade.
If this cannot be verified, the ARI system vitomatic initiation system should be modified in the short-term to meet the functional requirements listed below. For the longer term, the automatic initiation signals and circuits should be upgraded to meet safety-grade requirements as indicated in Recommendation GL-5.
(1) The design shoulo provide for the automatic inipiation of the auxiliary feedwater sys tem flow.
9 (2) The automatic initiation signLis and circuits should be designed so that a single failure will not result in the loss of auxiliary feedwater system functicn.
(3) Testability of :ne init a ti:n sign 2. anc circuits snall be a feature of the design.
(4) The initiation signals and circuits should be pcwered frca the emer-gency buses.
(5) Manual capability to initiate the auxiliary feedwater system from the control room should be retained and should be implemented so that a single failure in the manual circuits will not result in the loss of system functicn.
(6) The alternating current motor-driven pumps and valves in the auxfif ary feedwater system should be included in the autcmatic actuation (timultaneous and/or sequential) of the loads to the emergency buses.
(7) The automatic initiation signals and circuits shall be designed so that their failure will not result in the loss of manual capability to initiate the AFi sys tem from tne control room.
.1 response to this recommendation, the licensee stated in a letter dated January 25, 1980, that the Secuoyah AFd system is designed for autonatic start. There are three safety grade automatic start modes provided for the AFA system; loss of offsite power, safety injecticn actuation, and low-low steam generator level. 'de have reviewed the licensee's response and our evaluation of tne control grace design (shor:
. term) is presentec in Supplement No. I to tne SEL Ne icng term counterpart of this recommendation, GL-5 (Safety Grade Automatic Initiation) will be reviewed in detail and our evaluation will be contained in a supplement to this SER.
3.
Addi tional Short Term Recomendations 1.
Recommendation - The licensee should provide redundant level indication and low level alarms in the control room for the AFd system primary water supply, to allow tneoperator to anticipate the need to make up water or transfer to an alternate water supply and prevent a low pumo suction pressure condition from occurring.
The low level alarm set-point should allow at least 20 minutes for operator action, assuming that the largest capacity AFA pump is operating.
The licensee indicated in a letter dated January 25. 1980, that its main line of defense against low pump suction pressure is an automatic transfer to an alternate source of water, each AF4 system pump has its own safety grade instrumentation that will sense low pump sucticn pressure and automatically switch the pump suction to the alternate source. Additionally, the licensee stated that there is a level indicator in the main control room for each condensate storage tank. Level alams for eacn tank are actuated in the main control room for both " low" level and "Icw-low" level. The "lcw-low" level alarm warns the cperator of imminent tank emptying and occurs when 2.5 feet of water remains in the tank. The amount of water is sufficient to supply two motor driven cumos and the turbine-driven pump at full ficw,1760 gpm, for 17.6 minutes.
'de have reviewed the licensee's resconse and conclude that it meets the recuirements of this reccmmendation and is, therefore, acceptable.
. 2.
Recomendation (This recommendation has been revised from the criainal reccmmendation in NUREG-0611) - The licensee should perform a 48-hour endurance test on all APd system pumps, if such a test or continuous period of operation has not been accomplished to date. Following the 48-hour pump run, the pumps should be shut down and cooled down and then res tarted and run for one hour. Test acceptance criteria should include demonstrating that the pumps remain within design limits with respect to bearing / bearing oil temperatures and vibration and that pump room ambient conditions (temperature, humidity) do not exceed environmental qualification limits for safety-related equipment in the room.
In response to this recomendation, the licensed by letters dated January 25, 1980, and May 1,1980, indicated that it will perform the recommended AR pump test, if they have not been pre-viously conducted (TVA is presently reviewing existing records), prior to exceeding five percent of full power. The licensee further indi-cated that a test report with a sumary of the test conditions and the results of the tests will be provided within 30 days af ter all tests are comcleted.
Based on the above licensee's comitment, we conclude that the response to this recommendatioit is acceptable. However, we intend to evaluate the AM oumo test results to confirm that the Sequoyah AF4 pumos are acceptable.
If the test results are not acceptable, we will then require modifications and provide a safety evaluation regarding the tests and modifications.
- 1 2-3.
Recommendation - The licensee snould icole ent the folicwing requirements as specified by Item 2.1.7.b on page A-32 of NUREG-0573:
" Safety-grade indication of auxiliary feecwater ficw to each steam generator snill :e acovicec in :ne ::ntroi c:om.
The auxiliary feedwater ficw instrument channels shall be powered from the emergency buses consistent with satisfying the emergency power diversit; requirements for the auxiliary feedwater system set forth in Auxiliary Systems Branch Technical Position 10-1 of the Standard Review Slan, Section 10.4.9."
Our evaluation of the Auxiliary Feedwater Indication (2.1.7.5 -
NUREG-0578) regarding the ability of the design to satisfy the control grade requirements specified in the NUREG position and clarifications, is presented in Supplement No. I to the SER Part II.
The licensee has indicated that while the flow indication has not been classed as safety grade, it utilizes the same type of transmitters which are used in other safety grade circuits. The transmitters are mounted on two separate, seismically qualified panels and powered from power sources connected to the emergency power system. The cables are in low level signal trays and are kept separate from all power cables. We will evaluate this design regarding its ability to satisfy the safety grade requirements. Our evaluation will be presented in a supplement to this SER.
. 4
%comendation - Licensees,vith plancs anicn require local manual realign-ment of valves to conduct periodic tests on one AF4 system train, and there is only one remaining AF4 train available for operation should propose Technical Specifications to provide that a dedicated individual who is in communication with the control room be stationed at the manual valves. Upon instruction from the control rocm, this operator would realign the valves in the AF4 system train from the test mode to their coerational alignment.
In response to this recommendation, the licersee by letter dated January 25, 1980, indicated that there are three AF4 trains. During the pericdic tests of the AF4 system, only one flow control valve in the AF4 train being tested would be affected and there are still two AF4 trains available. As a result of the licensee's testing lineup, we ct;nclude that this recommendation is not applicable to Sequoyah.
C.
Long Tenn Recommendations 1.
Recommendation GL Licensees with plant designs in which all (primary and alternate) water supplies to the AF4 systems pass through valves in a single flow path should install redundant parallel flow paths (piping and valves).
In resconse to this recommendation, the licensee by letter dated January 25, 1980, indicated that the alternate water supplies to the AF4 pump suctions do not share the same flow path with any valves in the normal water supply lines. We have reviewed the licensee's response to this recontendation and conclude that it is acceptable.
.... 3.
Recommendation GL At least one AFW system pump and its associated flow path and essential instrumentation should automatically initiate AFW system flow and be capable of being ocerated independently of any ac power source for at least two hours. Conversion of d power to ac power is acceptab'.e.
In response to this rer.ommendation, the licensee indicated in a letter dated January 25, 1980, that the turbine driven auxiliary feedwater pumo is capable of operating for two hours without AC power, using only battery power for control and a DC powered rocm fan to remove heat frem the pump room. One potential concern has arisen regarding the AFW system level control during a station blackout.
During such an event, steam generator level control would be accomplished by manipulation of the level control valves using air from accumulators near the valves and some DC power. The licensee is planning to test this subsystem under simulated blackout conditions, and thus determine the time duration for which the accumulator air supply would be available. Because of the small likelihood of a station blackout occurring at Sequoyah in the near future and the existence nf procedures for manual control of the level control valves we conclude that the results of this test and any resulting modifications need not be required short-term. We intend to review the test results and if they are not acceptable, we will require modifications and provide a safety evaluation regarding the tests and modi fications.
,.. - 4. _ Recommendation iL Licensees having plants with unprotected normal AFW system water supplies should evaluate the design of their AP.4 systems to determine if automatic protection of the pumps is necessary following a seismic event or a tornado. The time available before pump damage, the alarms and indications available to the control room operator, and the time necessary for assessing the problem and taking action shvild be considered in determining whether operator action can be relied on to prevent pump damage. Consideration should be given to providing pump protection by means such as automatic switchover of the pump suctions to the alternate safety-grade source of water, automatic pumo trips on low suction pressure, or upgrading the normal source of water to meet seismic Category I and tornado protection requirements.
In response to this recommendation, tne licensee by letter dated January 25, 1980, stated that the Sequoyah AFW system design already provides for automatic transfer to an alternate water source on low suction pressure at the intake to the pumps. The alternate water source is the essential raw cooling water.
We have reviewed the licensee's resconse and conclude that it meets our recommendation and is, therefore, acceptable.
5.
Recommendation GL The licensee should upgrade the AFW system auto-natic initiation signals and circuits to meet safety-grade requirements.
In response to this recommendation, the licensee indicated in a letter dated January 25, 1980, that the present AFW system automatic initiation signals are safety grade. We will review the licensee's design in cetail and our evaluation will ce :ontair.ed in a supolement to this SER.