ML19260A008

Advises of NRC Requirements for Auxiliary Feedwater Sys. Generic & plant-specific Requirements Encl

ML19260A008
Person / Time
Site:	North Anna
Issue date:	09/28/1979
From:	Eisenhut D Office of Nuclear Reactor Regulation
To:	Proffitt W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
References
NUDOCS 7910260283
Download: ML19260A008 (21)

Text

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UNITED STATES

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5 %,. ( [,h NUCLEAR REGULATORY COMMISSf 0N "r

WASHINGTON, D. C. 20355

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September 28, 1979 Docket No.: 50-338 Mr. W. L. Proffitt Senior Vice-President - Power Virginia Electric and Power Company P. O. Box 26666 Richmond, Virginia 23261

SUBJECT:

NRC REQUIREMENTS FOR AUXILIARY FEE 0 WATER SYSTEMS AT NORTH ANNA POWER STATION, UNIT 1 The purpose of this le.tter is to advise you of our requirements for the auxiliary feedwater systems at the subject facility.

These requirements were identified during the course of the NRR Bulletins and Orders Task Force review of operating reactors in light of the accident at Three Mile Island, Unit 2. to this letter identifies each of the requirements >.pplicable to the subject facility. These requirements are of two types, (1) generic requirements applicable to most Westinghouse-designed operating plants, and (2) plant-specific requirements applicable only to the subject facility. contains a generic request for additional information regarding auxiliary feedwater system flow requirements.

The designs and procedures of the subject facility should be evaluated against the applicable requirements specified in Enclosure 1 to determine the degree to which the facility currently conforms to these requirements. The results of this evaluation and an associated schedule and conmitment for implementation of required changes or actions should be provided for NRC staff review within thirty days df receipt of this letter. Also, this schedule should indicate your date for submittal of information such as design changes, procedure changes or Technical Specification changes to be provided for staff review. You may also provide your response to the items in Enclosure 2 at that time.

In addition to the requirements identified in this letter, other requirements which may be applicable to the subject facility are expected to be generated by the Bulletins and Ordars Task Force. Such requirements are those resulting from our review of thr is-of-feedwater event and the small break loss-of-coolant accident as described in the Westinghouse report WCAP-9600, " Report on Small 7910260 2 8 3 1212 268

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s Mr. W. L. Proffitt September 28, 1979 Break Accidents for Westinghouse NSSS System." Our specific concerns include systems reliability (other than the auxiliary feedwater system),

analyses, guidelines and procedures for operators, and operator training.

We plan to identify, in separate correspondence, the requirements resulting from the additional items from the Bulletins and Orders Task Force review.

' Sincerely, l!<';ll;l,3~l

• ),/

(l (l ' ' '

D. Eisenhir,, Ac' tin'g 'Direc tor Division of Operating Reactors Office of Nuclear Reactor Regulation

Enclosures:

A. Stated 0

1212 269

Mr. W. L. Proffitt Virginia Electric and Powe. Company September 28,197C cc: Mr. Anthony Gambardella Mr. Michael S. Kidd Office of the Attorney General V.

S'. Nuclear Regulatory Commission 11 South 12th Street - Room 308 P. O. Box 128 Richmond, Virginia 23219 Spotsylvania, Virginia 22553 Richard M. Foster, Esquire Director, Technical Assessment Divisic 1230 A Pearl Street Office of Radiation Programs (AW-459)

Denver, Colorado 80203 U. S. Environmental Protection Agency Crystal 'iall #2 Michael W. Maupin, Esquire Arlingt;n, Virginia 20460 Hunton, Williams, Gay and Gibson P. O. Box 1535 U. S. Environmental Protection Agency P,ichmond, Virginia 23212 Region III Office ATIN:

EIS COORDINATOR Mrs. June Allen Curtis Building 412 Orens Drive 6th and Walnut Streets Huntsville, Alabama 35801 Philadelphia, Pennsylvania 19106 tir. James Torson Alderman Library 501 Leroy Manuscripts Department Socorro, New Mexico 87801 University of Virginia Charlottesville, Virginia 22901 Mrs. Margaret Dietrich Route 2, Box 568 Mr. Edward Kube Gordonsville, Virginia 22042 Board of Supervisors Louisa County Courthouse Ellyn R. Weiss, Esquire P. O. Box 27 Sheldon, Harmon, Roisman and Weiss Louisa, Virginia 23093 1725 I Street, N.W., Suite 506 Washington, D. C.

20006 Mr. J. B. Jackson, Jr.

Commonwealth of Virginia Mr. James C. Dunstan Ceuncil on the Environment State Corporation Commission 903 Ninth Street Office Building Commonwealth of Virginia Richmond, Virginia 23129 Bland'on Building Richmond, Virginia 23209 Mr. Paul W. Purdom Environmencal Studies Institute Mr. A. D. Johnson, Chairman Drexel University Board of Supervisors of Louisa County 32nd and Chestnut Streets Trevillians. Virginia 23170 Philadelphia, Pennsylvania 19104 1212 270

s fir. W. L. Proffitt Virginia Electric and Power Company September 28, 1979 cc:

Alan S. Rosenthal, Esquire Atomic Safety and Licensing Appeal Board U. S. Nuclear Regulatory Commission Washington, D. C.

20555 Michael C. Farrar, Esquire Atomic Safety and Licensing Appeal Board U. S. Nuclear Regulatory Commission Washington, D. C.

20555 Dr. John H. Buck Atomic Safety and Licensing Appeal Board U. S. Nuclear Regulatory Comnission Washington, D. C.

20555 Atomic Safety and Licensing Board Panel V. S. Nuclear Regulatory Commission Washington, D. C.

20555 1212 271

s ENCLOSURE 1 X.9 (W)

NORTH ANNA UNIT 1 AUXILIARY FEE 0 WATER SYSTEM X. '9.1

System Description

X.9.1.1 Configuration and Overall Design The auxiliary feedwater system (AFWS) is designed to supply water to the steam generators (SG) for reactor coolant system sensible anci decay heat removal when the normal feedwater system is not available.

The AFWS can be utilized during certain periods cf normal startup and shutdowns, in the event of malfunctions such as loss of main feed-water flow, loss of offsite power and also in the event of cn accident.

The AFW system is automatically initiated upon receipt of the following signals:

low steam generator level, safety injection, loss of offsite power, and main feed pump trip.

4 The AFWS is shown in simplified form in Figure 1 attached.

The system consists of two motor driven pumps (3A, 3B), and one steam driven turbine pump (2).

Each motor driven pump has a design fl7w of 350 gpm, the turbine driven pump has a design flow of 700 gpm but is orfice limited to 350 gpm when pumping in the normal lineup to SG-A.

Taps from each main steam line at a point upstream of the main steam isolation valves provide the source of steam to the turbine.

The motor driven pumps are connected to separate emergency power buses} $ =

s (Class 1E).* Normally the pumps take suction from the 110,000 gallon emergency condensate storage tank. This provides 8 hours of operation for decay heat removal. The emergency condensate storage tank is designed to seismic Category I requirements and is protected from tornado missiles. An additional supply of 300,000 gallons is available from a non-seismic condensate make-up storage tant. In addition to the 300,000 gallon supply, an unlimited supply of water is available from the seismic Category I service water and fire protection systems which are supplied from Lake Anna and the spray cooling pond, which is seismic Category I designed. Referring to Figure 1, each pump is lined up normally to a specific steam generator; pump 3B to SG B, 3A to SG C and 2 to SG A. The pumps can be aligned to other steam generators in the event of line breaks, pump failures, etc., by positioning the manual control valves to suit. ?FW flow to steam generator C is normally remote manually 4 controlled by an air operated valve. AFW flow to steam generators A and B is similarly manually controlled by an AC motor operated valve in each supply line. In the. event of loss of offsite and onsite AC power, realignment of manual valves is necessary to supply AFW flow to all steam generators from the turbine-driven pump. The instrument air supply system, for the air operated AFW flow control valves, includes a 16.7 cu. ft. accumulator tank charged to 100 psig. This capacity is sufficient to operate the air operated valve (s) from 30 minutes to 8 hours depending on frequency of valve adjustment. 1212 273

% X.9.1.2 Component Design Classification The turbine pump train and motor pump trains (110,000 gallon tank, pumps, valves, motors, piping, service water and fire protection systems) are seismic Category 1 and tornado missile protected, designed to Quality Group C. (Class lE for electrical equipment). The 300,000 gallon condensate make up tank is non-seismic. X.9.1.3 Power Sources The motor driven pumps and motor operated valves are supplied from the Class 1E A-C emergency buses which may be powered by the diesel generators, 3A from Emergency Bus IH, 3B from emergency bus lJ. The steam admission valves for the turbine pump are air-operated using DC solenoids and are energized from the emergency battery buses. Instrumentation and Controls The instrumentation and Control power supplies are from the 120 VAC 4 vital bus system. There are 4 vital buses, each supplied by an inverter from the 125 VDC power system. The motor driven pump breaker controls are powered.from the 125 VOC power system provided from the Class lE emergency DC buses. X.9.1.4 Controls Steam generator level is controlled remote manually from either the Main Control Room (MCR) or the Auxiliary Shutdown Panel (ASP) with safety grade instrumentation provided (level and flow indications). 1212 274 ~-

s The valves in the water flow lines to the steam generators consist of three motor operated valves from one he6 der and three air operated valves from the other header. Any pump can supply either header by operating manual valves in the pumps discharge. (For normal alignment refer to Section X.9.1.1.) The air operated valves are normally open and fail open on loss of power, the MOVs are normally open and fail as-is on loss of power. The MOVs or air operated valves are positioned by the operator to maintain proper level in the steam generators. The steam admission valves to the turbine are air operated, normally closed and fail open. These valves can be controlled from the MCR or ASP. X. 9.1. 5 Information Available to the Operator The following indications are available at both operating stations except as noted. 4 1. Position indication of the MOVs and air operated valves 2. Flow, gpm to each steam generator (Main Control Board (MCB)) only 3. Pump Current and Voltage (MCB only) 4. Steam Pressure to Aux feed pump turbine (MCB Only) 5. Steam Generator Levels 6. Pump Discharge and suction pressures (MCB only) 7. Breaker (motor driven pumps) position 8. Condensate storage tank level emergency ~1212 275

s X.9.1.6 Initiating Signals for Automatic Operations The following signals start the pump motors and open the steam con-trol valves to the turbine: l. Steam generator water level, low-low in any steam generator (2 out of 3 signals) 2. Safety Injection signal * (Delay of 35-60 seconds on Motor driven pumps) 3. Loss of offsite power 4. Main Feed pump trip (loss of all Main feed pumps) 5. Manual X.9.1.7 Testing The systems are tested periodically in accordance with tech spec requirements. The frequency of periodic testing is 31 days. In addition, the particular system is tested in accordance with the technical specifications af ter performina system maintenance. The systems are tested using the recirculating lines, with various plant parameters noted. (Suction and discharge pressure, etc.) The instrumentation systems are checked periodically, in accordance with the technical specifications, on a per shift, monthly or refueling time frame basis.

• There is no delay of the S.I. signal to the turbine driven pump control.

The reason for the delay in the motor driven pump control circuit is to limit the loads during emergency diesel generator loading. 1212 276

s X.9.1.8 Technical Specifications A review of the technical specifications indicated that these specifications cover limiting conditions of operation (LCO) and periodic surveillance testing consistent with standard Technical specifications. X.9.2 Reliability Evaluatio.i X.9.2.1 Dominant Failure Modes Successful delivery of feedwater is considered to be the flow of at least 350 gpm to one (or more) of the three steam generators for the transients considered here Failure modes of the AFWS were assessed for three types of initiating transients. The dominant failure modes for each transient type are discussed below. Loss of MFW with Offsite Power Available The reliability analysis of the North Anna AFWS based on this ini-tiating transient did not identify any single failures or double failures which would fail the entire AFWS. This assessment indicates the dominant AFWS failure mode to be a combination of the failure of both actuation trains to actuate their respective components, coupled with failure of the operator to detect the non-actuation of the system and to manually actuate it. 1212 277

.y-Loss of MFW with Only Onsite AC Power Available This transient is somewhat different in character than in the case above, in that reliance for AC power is now on the station diesel generators rather than offsite power. In essence, this edds failure modes such as diesel generator failure to start to the overall list of failure modes of trains of the AFWS. The dominant failure modes for the AFWS discussed for the above case are not dependent on the actual source of AC power (i.e., offsite vs. onsite). Thus the probability of the failure mode discussed above should not change. Further, the addition of the diesel generator failure mode to other train failure modes is not sufficiently important to make the probability of such a combination of modes significant. For these reasons,the AFWS failure probability for this case is still dominated by the coincident loss of both actuation trains, coupled with the failure of the operator to subsequently manually actuate the AFWS. Loss of MFW with Only DC Power Available In this case, no AC power (offsite or onsite) is available; the AFWS is thus reduced to the one steam-driven train for feedwater delivery. A number of single failures within thir train can fail the AFWS (e.g., hardware failure in the pump and valves, control system failures, etc.). The dominant failure mode for this train is that the train is out of eervice for maintenance when the transient occurs. 70 \\2\\2 7to

s X.9.2.2 Principal Dependencies The potential for location dependencies was noted during this reliability evaluation, in that some portions of the AFWS were located in common rooms. However, because no location dependencies were found which could potentially affect all trains of the AFWS, these dependencies do not appear to be & significant concern. XIII.9.3 Recommendations for this Plant The short-term recommendations (both generic, denoted by GS, and plant-specific) identifjeo in this section represent actions to improve AFW system reliability that should be implemented by January 1, 1980, or as soon thereafter as is practicable. In general, they involve upgrading of Techni al Specifications or establishing procedures to avoid or mitigate potential system or operator failures. The long-terr.,both generic, .fenoted by GL, and plant-specific) recommendations identified in this sec-tion involve system design evaluations and/or modifications to improve AFW system reliability and represent actions that should be implemented by January 1, 1981, or as soon thereafter as is practicable. X.9.3.1 Short Term 1. Recomendation GS Emergency procedures for transferring to alternate sources of AFW supply should be available to the plant operators. These ~ procedures should include criteria to inform the operator when, and in what order, the transfer to alternate wate.r sources should take place. The following cases should be covered by the procedures: e The case in which the primary wat1r supply is not initially 1212 779

% avail able. The procedures for this case should include any operator actions required to protect the AFW system pumps against self-damage before water flow is initiated; and. e The case in which the primary water suppl; is being depleted. The procedure for this case should provide for transfer to the alternate water sources prior to draining of the primary water supply. 2. Recomendation GS The licensee should confirm flow path avail-ability of an AFW system flow train that has been out of service to perfom periodic testing or maintenance as it,ilows: o Procedures should be implemented to require an operator to determine that the AFW system valves are properly aligned and a second operator to independently verify that the valves are properly aligned. e The licensee should propose Technical Specifications to assure that prior to plant startup following an extended cold shutdown, a flow test would be performed to verify the normal flow path from the primary AFW system water source to the s h am generators. The flow test should be conducted with AFW system valves in their normal alignment. 3. Recommendation GS The licensee should verify that the automatic start AFW signals and associated circuitry are safety 1212 280

s grade. If this cannot be verified, the AFW system automatic 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 snould be upgraded to meet safety grade requirements as indicated in Recommendetion GL-5. ~ The dcsign should provide for the automatic initiation of the auxiliary feedwater system flow. The automatic initiation signals and circuits should be designed so that a single failure will not result in the loss of auxiliary feedwater system function. Testability of the initiation signals and circuits shall be a feature of the design. The initiation signals and circuits should be powered from the emergency buses. 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 function. The alternating current motor-driven pumps and valves in the auxiliary feedwater system should be included in the automatic actuation (simultaneous and/or sequential) of the loads to the emergency buses. The auto n tic initiation signals and circuits shall be designed so that their failure will not result in the loss of manual capability to initiate the AFW system from the }2f2 28l control room.

s X.9.3.2 Additional Short-Term Recomendations The following additional short-tem recomendations resulted from the staff's Lessons Learned Task Force review and the Bulletins and Orders Task Force review of AFW systems:at Babcock & Wilcox-designed operating plants subsequent to our revies. of the AFW system designs at W-and C-E-designed operating plants. They have not been examined for specific applicability to this facility. 1. Recomendation - The licensee should provide redundant level in-dications and_ low level alarms in the control room for the AFW system primary water supply to allow the operator to anticipate the need to make up water or transfer to an alternate water supply and prevent a low pump suction pressure condition fror occurring. The low level alam setpoint should allow at least 20 minutes for operator action, assuming that the largest capacity AFW pump is operating. 2 Recomendation - The licensee should perfom a 72-hour endurance test c all AFW system pumps, if such a test or continuous period of operation ' has not been accomplished to date. Following the 72-hour pump run. . the pumps should be shut down and ccoled down and than restarted and run for one hour. Test acceptance criteria should include demonstratin-that the pumps remain within design limits with respect to bearing / bearing oil temperatures and vibration and that pump room ambient cond-tions ( temperature, humidity) do not exceed environmental qualificatic limits for safety-related equipment in the reor.. 1212 282

s 3. Recommendation - The licensee should implement the following requirements as specified by Item 2.1.7.b on page A-32 of NUREG-0578: " Safety-grade indication of auxiliary feedwater flow to each ste'n generator shall be provided in the control room. The auxiliary feedwater flow instrument channels shail be powered from the emergency buses consistent with satisfying the emergency power diversity requirements for the auxiliary feedwater system set forth in Auxiliary Systems Branch Techn-nical Position 10-1 of the Standaid Revien-P %, Section 10.4.9." 4. Recommendation - Licensees with plants which require local manual realignment of valves to conduct periodic tests on one AFB system train and which have only one remaining AFW 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 room, this operator would re-align the valves in the AFW system train from the test mode to its operational alignment. k.9.3.3 Long Term Long-term recommendations for improving the system are as follows: 1. Recommendation - GL The licensee should upgrade the AFW system automatic initiation signals and circuits to meet safety grade requirements. 1212 283

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Basis for Auxiliary Feedwater System Flow Reauirements As a result of recent staff reviews of operating plant Auxiliary Feed. water Systems (AFL'S), the staff concludes that the design bases and criteria provided by licensees for establishing AFW5 requirements for flow to the steam generator (s) to assure adequate removal of reactor decay heat are nQt well defined or documented. We require that you provide the following ATWS fica design basis infor-mation as applicable to the design basis transients and accident con-ditions for your plant. Identify the plant transient and accident conditions considered 1. a. in establishing AFWS flow requirements, in:.luding the following events:

1) Loss of Main Feed (LMFJ)

2) LMFW w/ loss of offsite AC power

3) LMFW w/ loss of onsite and offsite AC power

4) Plant cooldown

5) Turbine trip with and without bypass

6) Main steam isolation valve closure

7) Main feed line break

8) Main steam line break

9) Small break LOCA

10) Other transient or accident conditions not listed above b.

Describe the plant protection acceptance criteria and corres-ponding technical bases used for each initiating event identi-fied above. The acceptance criteria should address plant limits such as: 1212 285

- Maximun RCS pressure (PORY or safety olve actuation) - Fuel temperature or damage limits (D~.6, PCT, maxir.um fuel central temperature) - RCS cooling rate limit to avoid excessive coolant shrinkage - Minimum steam generator level to assure sufficient stea:n generator heat transfer surface to remove decay heat and/or cool down the primary system. 2. Describe the analyses and assumptions and corresponding technical ~ justification used with plan condition cons:dered in 1.a. above including: Maximum reactor power (including instrument error allowance) a. at the time of the initiating transient or accident. b. Time delay from initiating event to reactor trip. Plant parameter (s) which initiates AFWS flow and time delay c. between initiating event and introduction of AFWS flow into steam generator (s). d. Minimum steam generator water level when initiating event occurs. Initial steam generator water inventory and. depletion rate before e. and after AFWS flow comences - identify reactor decay heat rate used. 1212 286

s Maximum pressure at which steam is released from steam generator (s) f. and against which the AN pump must develop suf ficient head. Minimum number of steam generators that'must receive AFW flow; 9 e.g.1 out of 2?, 2 out of 4? RC flow condition - continued cperation of RC pumps or natural h. circulation. i. Maximum AW inlet temperature. j. Following a postulated steam or feed line break, time delay assumed to isolate break and direct AW flow to intact steam generator (s). AW pump flow capacity allowance to acconmodate the time delay and maintain minimum steam generator water level. Also identify credit taken for primary system heat removal due to blowdown. Volume and maximum temperature of water in main feed lines k. between steam generator (s) and AFWS connection to main feed line. Operating condition of steam generator nomal blowdown following 1. initiating event. Primary and recondary system water and metal sensible heat m. used for croldown and AFW flow sizing. Time at hot standby and time to cooldown RCS to RER system cut n. in temperature to size AFW water source inventory. 1212 287

', t, 4s 3. Verify that the AFJ pumps in your plant will supply the necessary flow to the steam generator (s) as detemined by items 1 and 2 above considering a single failure. Identify the u rgin in sizing the pump flow to allow for pump recirculation flow, seal leakage and pump wear. t 1212 288 .}}