ML20207J033

Discusses Resolution of Generic Issue 124 Re Auxiliary Feedwater Sys Reliability.Resolution Relied on Audit of Serveral Parameters That Effect Availability & Reliability of Auxiliary Feedwater Sys

ML20207J033
Person / Time
Site:	Arkansas Nuclear
Issue date:	08/24/1988
From:	Craig Harbuck Office of Nuclear Reactor Regulation
To:	Tison Campbell ARKANSAS POWER & LIGHT CO.
References
REF-GTECI-124, REF-GTECI-NI, TASK-124, TASK-OR TAC-68188, NUDOCS 8808300188
Download: ML20207J033 (11)

Text

,9 ,,, a UNITED STATES )

NUCLEAR REGULATORY COMMISSION

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• g August 24, 1988 i Docket No. 50-313 Mr. T. Gene Campbell i Vice President. Nuclear Operations  ;

Arkansas Power and Light Company P. O. Box 551

Little Rock. Arkansas 72203

SUBJECT:

ARKANSAS NUCLEAR ONE. UNIT 1 (ANO-1) - RESOLUTION OF GENERIC ISSUE (GI) 124 - AUXILIARY FEEDWATER SYSTEM RELIABILITY (TAC NO. 68188)

Anauxiliaryfeedwater(AFW)systemreviewhasbeenconductedtoassessthe overall reliability for each of seven plants with a two train AFW system under l

GI-124. Auxiliary Feedwater System Reliaoility. This effort includes a plant- '

specific review and an en-site audit of the AFW system, and calculated estimates

of the reliability of the AFW system given various initiating events. The staff utilized this approach to resolve GI-124 rather than a strictly analytical l approach because it believed that a first-hand audit of the AFW system design and operation more directly addressed the root causes of AFW system unrvailability l 1

and unreliability.

In general, the resolution approach adopted by the staff relied on an a,iit of several parameters that affect the availability and reliability of the ka'

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system. These parameters include design configurations; maintenance, surveil-  !

lance, and testing procedures and practices; operating procedures; personnel 1 training; system layout; operating experience; instrumentation art control; and environment and accessibility for operator recovery actions following potential malfunctions. The Standar reliabilitycriterion(10"gReviewPlan(SRP)Section10.4.9AFWsystemnumerical to 10'S per demand) served as the bisis for concluding that the AFW system in the seven plants of concern was acceptably reliable.

Because the SRP criterion specifies consideration of compensating factors such as other reliable decay heat removal methods to ,iustify a larger AFW system

, unavailabilii;y the Gff evaluated compensatory features as part of its

effort.

A detailed review of malatenance, procedures and training was not conducted for ANO-1 since licensee programs and practices in these areas are the same as those for ANO-2 which was previously evaluated in detail for GI-124 resolution.

The licensee satisfactorily addressed the issues in these areas during the  !

ANO-2 GI-124 review. Further, a detailed review of AFW instrumentation and  !

control was not conducted because of past staff reviews of the emergency  !

feedwater initiation and control system at Crystal River and Rancho Seco wtiich are very similar to that at ANO-1.

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'- I Mr. T. Gene Campbell  !

Eased on its review, the staff concludes that the ANO-1 AFW system, in conjunc-tion with the Startup feedwater pump as a corpensatory decay heat removal l!

feature, provides sufficient reliability to meet the unavailability criterion of SRP Section 10.4.9 for the more frequently occurring transients such as loss of  :

main feedwater, and therefore, this issue is considered resolved for ANO-1.  !

The report docunenting the staff review under GI-124 is enclosed for your  !-

infortation-Sincerely, j

\

\T !t l C. Craig Harbuck, Project Manager l Project Directorate - IV l

! Division of Reactor Projects - III, [

IV, V and Special Projects

Enclosure:

As stated j cc w/encicsure: I See next page l

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i DISiRIBUTION  !

-ITocket File  !

NRC F0R  !

Local PCR PD4 Reading f

L. Rubenstein ,

J. Cabo  !

P. Noonan  ;

C. Harbuck OGC-Rockville l E. Jordan >

B. Grires i ACRS(10)  !

PD4 Plant File  ;

1 FD4/L4ht PD4/FM M PD4/D TN i FNcenin tuck:sr JCalvo Cty{lt8 CHarhlE8 08$ G8/Lyl88 l

e Mr. T. Gene Carpbell ,

Eased on its review, the staff concludes that the ANO-1 AFW system, in conjunc-tion with the startup feedwater purp as a conpensatory decay heat removal 4 feature, provides sufficient reliability to meet the unavailability criterion of SRP Section 10.4.9 for the more frequently occurring transients such as loss of r.ain feedwater, and therefore, this issue is considered resolved for ANO-1.

The report documenting the staff review under GI-124 is enclosed for your inferr.a tion.

Sincerely.

G 1 C. Craig Harbuck, Project Manager Project Directorate - IV Division of Reactor Projects - !!!,

IV, Y and Special Projects

Enclosure:

As stated cc W/ enclosure:

See next page  !

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Mr. T. Gene Campbell Arkansas Power & Light Ccepany Arkansas Nuclear One Unit 1 -

CC: t Mr. Dan R. Howard, Manager Licensing Arkansas Nuclear One P. O. Box 608 Russellville, Arkansas 72801 Mr. James M. Levine, Executive Director Nuclear Oserations Arkansas Nuclear One P. O. Box 608 Russellville, Arkansas 72801 Mr. Nicholas S. Reynolds ,

Bishop. Cook, Purcell & Reynolds i 1400 L Street, N.W.

Washington, D.C. 20005-3502 Mr. Robert B. Eersum Babcock & Wilcox Nuclear Power Generation Division ,

1700 Rockville Pike, Suite 525 Rockville, Maryland 20852 ,

Resident inspector ,

U.S. Nuclear Regulatory Comission i 1 Nuclear Plant Road Russellville Arkansas 72801 ci Re$.onal U. Administrator.

Nuclear Region IV Regulatory Comission Office of Executive Director for Operations 611 Ryan Plaza Drive Suite 1000 l Arlington, Texas 76011 j l

Mr. Frank Wilson, Director  :

Division of Environmental Health i Protection De>artment of Health Ar(ansas Department of Pealth 4815 West Harb> treet Little Rock, v is 72201 Honorable V iiw sernathy County Juon P 4 County Pope County .ious e Russellville, Arkansas 72801 l

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ARKANSAS NUCLEAR ONE, UNIT - 1 AUXILIARY FEE 0 WATER SYSTEM RELIABILITY ASSESSFENT A. Sumary and Conclusions This repo.t contains the staff's assessment of the overall reliability of the auxiliary feedwater system (AFWS) for Arkansas Nuclear One, Unit 1 (ANO-1).

This review was perfomed in ccnnection with resolution of Generic Issue (GI) 124. "Auxiliary Feedwater System Reliability " which addresses AFWS reliability in certain plants.

AFWS reliability analyses indicated that many plants fell in the high reliability range as defined by the staff in the Standard Review Plan, however, several plants fell in the lower reliability range. While these plants met applicable licensino requirements for the AFWS, their system reliability was still in question. Som licensees for this latter grcup of plants irplemented modificatters to increast AFWS reliability to an acceptable range. However, AFWS reliability for seven plants rerM ned questionable. The plants in this category are Ah0-1 and 2, Crystal River, Ft. Calhoun, Prairie Island Units I and 2, and Rancho Seco.

The objective of the review under GI-124 is to evaluate the AFWS reliability for these seven plants and to document any recomendations for further licensee BCtions.

The resolution apprcach adopted by the staff in its review of ANO-1 relied on an audit of several plant features that affect the availability and reliability of the AFW system in addition tc an assessment of numerical unavailability.

Thesevariablesincludedesignconfiguraticts;raintenance,surveillanceand testing procedures and practices; crerating precedures; personnel training; operating experierce; instrumentation and controit and environment and acces-sibility for operator recovery actions fo The AFWS numerical reliability criterion (10'}1owing~gotential to 10 per demand) malfunctions.

given in Section 10,4.9 of the Standard Review Plan (SRP) served as the basis for evaluating the AFWS in the seven plants of concern. The SRP criterion specifica stat "An acceptable AFWS should have an unavailability in the range of 10~}']to 10'gs:

per demand based on an analysis usi.9 rethods and data : resented in h0 REG-0611 and NUREG-0635. Compensating factors such as other met 1ods of accomplishing the safety functions of the AFKS or other reliable rethods for cooling ti; aactor core during abnomal conditions may be considered te justify a larger uaavail-ability of the AFVS." For the plants under consideration in GI-124, the focus of the cencern for adequate AFWS reliability was on the more frequently occurring challenges to the the system such as loss of main feedwater. Further, because the SRP criterion specifies censideration of compensating factors such as the availability of other reliable decay heat removal methods to justify a larger AFVS unavailability, an evaluation of compensatory features was also conducted.

When detemining whether or not to give credit for corpensatory decay heat removal features, the staff position has been and continues to be that only features which relate to secondary side decay htat removal capability (e.g. a startup feedwater pump. AFV purp discharge crossconnections between units, or a third AFW pump) can be considered acceptable for satisfying the SRP criterien.

While the staff recognizes the capability to remove decay heat in the "feed-and-bleed" mode utilizing the primary system safety / relief valves and high pressure

injection purps, such a method involves large uncertainties in operator respense.

Therefore, it is considered to be a suitable backup to the AFWS in emergency procedures as a last resort for decay heat removal, but is not sufficiently reliable to justify it as a compensatory feature in order to rett the SRP goal for AFWS reliability.

The staff did not undertake a atailed review of maintenance, operations (emergency procedures) and training at ANO-1. The licensee's practfees in these areas for ANO-1 are essentially the same as those previously covered in the review of GI-124 for ANO-2. 86cause the outstanding issues in these areas were resolved as discussed in the G1-124 report for ANO-2, no further discussion is included in this report.

It should also be noted that a separate section is not included on instrurentation and control. This is because the emergency feedwater initiation and control (EF10) system at ANO-1 is very similar to the same syster provided at Crystal River and Rancho Seco which have already received extensive detailed staff review. EFIC is a fully safety-related system for automatic AFW system initiation and control and meets staff criteria under item II.E.1.2 of NUREG-0737.

The licensee indicated to the staff during discussions regarding resolution of GI-124 that substantial modifications and improveu nts have been made to .

the AFW syt, tem since 1980 (see Fi vre 3). These include provision for a back-up suction supply from the service water system, replacement of the AFW pump turbine driver and associated turbine centrol improtements, installation of the safety related emergency feedwater initiation and control (EFIC) systen and associated 0TSG instrumentation, installation of new AFW suction and ,

discharge piping and valves, installation of safety related flow indication, i and installation of the "Q" (safety-related) condensate storage tank. These improvements were r4de as part of the post-TMl upgrades to the system imposed by the staff under items II.E.1.1 and II.E.1.2 of NUREG-0737, Clarification of TIM Action Plant Requirements. Some of the miodifications were not a result of specific NRC requirements but resulted from the licensee's reccgnition of the importance cf reliable AFW capability. The staff concurs with tha licensee that the redifications have improved AFW system reliability.

However, as discussed subsequently in this report, despite the above modifica-tions, the licensee concluded that the auxiliary feedwater system numerical unavai-a review of 1 ability will not compe.nsating meet for features thedecay explicit heatSRP criterion.

removal Consequently,licenset was performed. The indicated that the startup feedwater pump provides an additional means to deliver water to the steam generators in the event of a loss of main and Nr.iliary (emergency)feedwater. Use of this purp is clearly discussed in ;. lent emergeticy operating procedure No. 1202-01. The licensee also noted that the high hesi.

safetyinjectionpupsprovideacapabilitytorecovesufficientdecayheatin the "feed-and-bleed mode. Based on staff review of the startup feedwater pump, the staff concludes that it serves as a sufficiently reliable carpensatory decay heat removal feature and, when considered in conjunction with the AFW system, adequately reliable secondary side decay heat removal capability is derenstrated. Therefore, GI-174 is resolved for ANO-1. Additional discussion of the startup feedwater pump is provided in Section F. of this report.

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The staff also finds that the AFU system design and operation adequately I consider other staff generic concerns raised within GI-124 (i.e., GI-68 with respect to environmental qualifications of the motor driven AFW pump, GI-93 l with respect to steam binding of the AFW pumps, GI-122.1.a,b, and c with respect to isolation valve failure, and interruption and recovery of AFW flow, GI-122.2 with respect to initiation of "feed-and-bleed," and GI-125.II.1.b with respect to single failure protection).

B. Introduction This report discusses the staff's assessment of the Auxiliary Feedwater System (AFWS) reliability for Arkansas Nuclear One, Unit 1 (ANO-1). This review was done in connection with the resolution of of Generic Issue (GI) 124 GI-124 "Auxiliary Feedwater System Reliability," addresses the reliability of the AFWS in certain plants. Reliability analyses

• for AFWSs indicated that many plants fell in the high reliability range as defined in the Standard Review Plan, NUREG-0800 However, several plants fell in the lower reliability ranges. Licensees for some of these plants implemented sufficient modifications to increase their AFUS reliability to an acceptable range. However, the reliability of the AFWS for seven plants, including ANO-1, remained questionable. The six other plants are ANC-2, Crystal River, Ft. Calhoun, Prairie Island, Units 1 and 2, and Rancho Seco.

The objective o' this task is to determine whether the AFWS of each of the subject seven plants is sufficiently reliable and to docurrent any recomrren-dations for further licensee or staff actions.

This report presents the issue resolution approach and evaluation philosophy in Section C, and detailed evaluations in Sections 0,E and F. The summary and conclusions are presented in Section A of this report.

C. Resolution Approach The staff believes that a high degree of availability and reliability for the AFWS can only be achieved if such a system is adequately designed, properly maintained and well operated. Proper maintenance and operating practices help reduce component failures. These practices are enhanced by good training programs for the maintenance and operations personnel. Good training programs also help the operations personnel understand the system's capabilities and its importance to safety. System understanding reduces failure due to maloperation of equipment and improves the likelihood of recovery in case of unanticipated component failures.

As indicated previously, detailed reviews of maintenance, emergency procedures and training as they relate to the ANO-1 AFP system were not conducted as part

• NUREG-0611, and NUREG-0635, Generic Evaluation of Feedwater Transients and Small Break LOCAs in Westinghouse and CE Designed Plants, respectively, and NRC rremoranda from A. Thadani to 0. Parr dated October 17, 1983, October 23, 1983, and November 9, 1984

of the specific review ' r ANO-1 because of the applicability of the plant practices and staff re.abw in these areas previously completed under the GI-124 review for ANO-2. Thus, no discussion is provided in this report related to these aspects of the AFW system. Specific discussion is provided on the systemdesignandconfiguration(SectionD),systemwalkdown(SectionE),and operating experience and reliability analysis (Section F).

The approach to resolution adopted by the staff as previously indicated is based on a deterministic assessment of the AFW system design, maintenance and operation in order to ensure its optimum availablity and performance. The sysym numet(cal unavailability is then compared against the SRP criterion (10 to 10 ~ per demand), and con.;ideration of appropriate reliable compensa-tory decay heat removal features is included as necessary. The specifics of this review are provided in subsequent sections of this report.  ;

D. Design and Configuration The staff conducted a review of the design and configuration of the ANO-1 AFW system. The staff met with the licensee to discuss the ANO-1 AFW system design and its compliance with the criteria of Standard Review Plan Section 10.4.9.

A walk-down of the AFW system was also conducted by the staff to verify that the as-built configuration was in accordance with the design.

1 ANO-1 is a Babcock and Wilcox designed reactor, with two once-through steam i generators, two FFW trains (each with a turbine-driven pump), and three l motor-driven condensate pumps. In addition, a startup feedwater pump is  ;

provided for use during normal plant startup and shutdown. The reactor is 1 located in a large dry reinforced concrete containment. The plant is provided l with two 100% capacity diesel generators for power to shutdown cooling systems if offsite power is lost.

The ANO-1 AFW system is a two-train system (refer Figure 4 for a system design summary). One train contains a centrifugal pump driven by an electric motor  ;

(P78) and the other train contains a steam turbine driven pump (P7A). Diversity l in pump drivers eliminates common mode failures in the AFWS motive power. The l AFW system configuration and turbine steam supply is shown in Figures land 2 l respectively. The pumps, P7A and P78, are identical. At rated flow, each pump is capable of providing a minimum of 720 gpm which is sufficient for removing i decay neat loads in excess of 3 percent of rated thermal power. The plant is i also equipped with a steam bypass system. Each of the is equipped with an atmospheric steam dump valve (ADV) plant's upstream two of the steam main lines steam isolationvalve(MSIV). This arrangement makes the dump valves operable even if the MSIVs are closed. The electric motor driver is capable of being powered from the B emergency diesel generator. The valves in the turbine driven train to each OTSG are de powered to ensure AFW flow in the event of a loss of all ac power.

The steam turbine driver for P7A is a single stage, solid wheel, non condensing, horizontal, split cast Terry turbine unit. It is designed for variable speed operation and is equipped with an electrohydraulic actuator for speed control, an overspeed trip mechanism, and an integral trip throttle valve. It is also

. - designed for rapid starting and will operate with steam generator pressures ranging from 1,100 psia to 60 psia. An electronic speed control system with a ramp feature and step open feature on the steam admission valves are provided to reduce the possibility of overspeeding the turbine. The steam admission valves are located outside the AFW pump room, and therefore, the steam supply line is not normally pressurized thereby precluding the need for high energy line break protection. Steam can be supplied to the turbine driver from either or both steam headers. Steam traps are installed on the turbine steam supply lines to continucusly remove any condensate. The turbine exhausts to the atmosphere.

Cooling water for the turbine lube oil cooler is piped from the pump suction.

Pump and motor bearings do not require auxiliary cooling.

The AFWS is not used for normal plant startup or shutdown, but is on standby for emergency conditions. Suction for the AFW pumps is provided by the seismic category I "Q" condensate storage tank through redundant locked open manual valves. A backup supply is also available from the nonseismic condensate storage tank through a locked closed manual valve and from each loop of the seismic Category I service water system through redundant normally closed motor operated valves. A minimum of 160,000 gallons of water in the "Q" CST is required to be available by technical specifications. In addition, the "Q" CST is prcvided with a tornado missile barrier wall which protects e minimum of 30 minutes of AFV supply to permit time for the operator to transfer manually to the service water backup in the event of CST failure in a tornado. A pump minimum flow recirculation line is provided with an orifice which returns to the CST for pump protection. In addition, a full flow recirculation test line to the CST is also provided. The valves in the test line are normally closed and close on receipt of an AFW initiation signal.

The AFWS discharge piping and valving arrangement is designed to allow either pump to supply water to either or both steam generators. The discharge line valves are normally open. Each line to each steam generator is provided with a de powered solenoid operated ficw control valve and an AC powered motor opera-ted valve to ensure isolation of a faulted steam generator, and feed flow to the intact steam generator as required during emergency operation following a postu-lated main steam or feedwater line break. The valves are powered from redundant supplies thus ensuring flow in the event of a single failure. Backleakage of steam / hot water in the AFW lines is prevented by three check valves in series.

The AFW discharge lines are also checked for high temperature each shift to ensure tha; unacceptable backleakage is not occurring and potential steam binding of the pumps is avoided.

Automatic initiation and control of AFWS is provided by the emergency feedwater initiation and control (EFIC) system (refer to Figures 5, 6 and 7). EFIC is a safety related control system which ensures initiation and continuous control of auxiliary feedwater flow to an intact steam generator in the event of loss of main feedwater, loss of reactor coolant pumps (loss of offsite power) or low level in an OTSG. EFIC also controls the steam exhaust path by modulating the atmospheric dump valves. The ANO-1 EFIC system is very similar to that provided at Crystal River and Rancho Seco. Details on the EFIC design are provided in the Crystal River GI-124 report, and the Rancho Seco restart safety evaluation, NUREG-1286.

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. . In r.he event of a complete loss of the AFW system, other methods are available ,

to remove decay heat, including (1) use of the startup feedwater pump, (2) i condensate pumps and (3) "feed-and-bleed." Use of these alternate decay heat .

removal methods is addressed in the plant emergency procedure. I l

On the basis of this evaluation, the staff concludes that the AFW system at l ANO-1 complies with the applicable criteria of Section 10.4.9 of the Standard l Review Plan, including the guidelines of NUREG-0737, Item II.E.1.1. The staff notes that use of the startup feedwater pump, condensate pump, and "feed-and-bleed" capability are effective means of decay heat removal and enhance the plant's overall capability of decay heat removal. Use of the startup feedwater pump as a compensatory decay heat removal feature has been considered and is discussed further in this report.

1 E. Syste.m Walkdown As part of the staff's review, a site visit and AFW system walkdown was conducted.

The walkdcwn afforded the staff the opportunity to examine the as-built system configuration, specific components, and potential for undesirable system inter-actions. The system walkdown had two main objectives. One was to confirm that the installed system conformed to the staff's understanding of the system design basis as identified in previous evaluations, and to determine if the system may be subject to conotn node failure nechanisms or harards (e.g. , flooding, fire, 1 missiles,suctionstrainers,etc.). The other main objective was to examine the ease of operator access to equipment for performing potential recovery actions. ,

This includes assessment of local emergency lighting, connunications, and other I factors (e.g., cleanliness, equipment labeling, use of locking devices, posting of simple instructions at equipment locations, etc).

The walkdown covered the piping and component layout from the condensate storage tanks, through the pumps to the containment penetration and included the turbine I driven AFW pump steam supply lines, switchgear, and the instrumentation ar.d con- l trol provided in the control room. Based on the walkdown, the staff identified no areas of concern regarding the as-built AFW system configuration, common mode failure potential, or ease of access for recovery actions.

F. Operating Experience _ and_ Reliability _ Analysis

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As part of the staff review under GI-124 for ANO-1, the staff discussed AFW component failure history, feedwater transient experience and AFW system numerical reliability evaluation with the licensee.

Since 1984, only two AFW component failures have occurred, both in 1985 (refer l to Figure 9). Prior to that time, five random component failures occurred in l 1983 and six in 1981. Four of the six failures involved the turbine driven pump, but these were corrected with the installation of a new turbine driver in 1982. The recent experience indicates that the licensee prograns for ensuring AFW component operability are effective as no failures have occurred I since 1986.

A review of unanticipated reactor trip experience for ANO-1 since 1981 indicated '

a high of 8 per year in 1983 and 1985, but only two per year in 1986 and 1987, and one in the first six months of 1988 (refer to Figure 10). Further, with

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. . the exception of 1985, an average of less than two trips per year relate to main feedwater system upsets. The six main feedwater upsets which occurred in 1985 are attributable to startup difficulties experienced with installation and tuning of the EFIC system. The licensee indicated their consnitment to improve main feedwater system performance and reduce reactor trips as part of their efforts during implementation of the B&W Owners Group Safety Performance Improve-ment Program reconsendations. The staff concludes that the most recent trip experience and continued licensee efforts have/will contribute to reduced chal-lenges to the AFW system.

As was stated previously, the licensee indicated that a update of the relia-bilityanalysisforthecurrentAN0-1AFWsystemaccountingfgrtherecent modifications resulted in a numerical unavailability of 4X10 per demand for a loss of main feedwater using the NUREG-0611 data base and methodology as specified in the SRP criter This value exceeds the acceptancecriterionof10jon(refertoFigure8).

per demand and thus necessitated consideration of other compensatory decay heat removal features. To address compensatory features, the licensee pointed out that the existing Emergency Procedure 1202.01 section dealing with overheating identifies a hierarcy for decay heat removal capability following transients and accidents (refer to Figure 11). Included in this pro-cedure as the first means following a loss of main feedwater is the startup feed-water pump. This pump provides full AFW flow at above the normal secondary side pressure when operated in series with a concensate pump. It serves as the normal means of plant startup and shutdown. This capability is available in addition to use of a condensate pump alone upon OTSG depressurization, use of a service water pump for service water addition to the OTSG upon depressuriza-tien, and "feed and bleed" cooling. "Feed and bleed" cooling requires only a single high pressure injection pump since it has the capability to lift the primary system safety valves.

Based on the above, the staff concludes that the startup feedwater pump serves as a suitably reliable compensatory feature for decay heat removal to justify a calculi.ed r AFW system unavailability lower than the SRP acceptance criterion, and therefore, the AFW system supplemented by the startup pump meets the SRP numerical reliability criterion for the more frequently occurring transients such as loss of main feedwater. The staff, therefore, considers GI-124 resolved for ANO-1.

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