ML20247J921

Forwards Rept Re Investigation Into Condition of Svc Water Sys at Facility & Plans for Further Activity.Sys Capable of Performing Required Functions

ML20247J921
Person / Time
Site:	River Bend
Issue date:	05/22/1989
From:	Booker J GULF STATES UTILITIES CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
RBG-30927, NUDOCS 8906010162
Download: ML20247J921 (6)

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ll GULF STATES UTELITIES COMPANY. ,

MVER BEND STATION POST OFFICE BOX 220 ST FRANCISVILLE. LOU 1$1ANA 70775 ARE A CODE 604 635 < 6094 346 866t -

May 22, 1989 '

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RBG- 30927 File Code G9.5, G9.25.1.5 i U. S. Nuclear Regulatory Commission Document Control Desk Washirgton, D.C. 20556 Gentlemen:

River Bend Station - Unit 1 Docket No. 50-458

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For your information, Gulf States Utilities (GSU) Company is providing the attached report concerning the investigation into the condition of the service water ; system at River . Bend Station (RBS) and plans for further activity. As a result of the investigation and analysis performed on the service water system during this refueling outage, GSU has determined that the system remains capable of performing its required functions. Continued efforts by RBS personnel described herein will ensure that the required functions of the system are maintained throughout the upcoming operating cycle.

If you need additional information, please contact Mr. L. A. England'at (504) 381-4145.

Sincerely, f , $< hY")

J. E. Booker.

( Manager-River Bend Oversight

,4 River Bend Nuclear Group

-JEB/L E/ FS/DAS/ch Attachment >

cc: U. S. NLelear Regulatory Commission Region IV 611 Ryan . Plaza Drive, Suite 1000 Arlington, TX 76011 Senior Resident Inspector P.O. Box 1051 St. Francisville, LA 70775 8906010162 890522 PDR ADOCK 05000458 i I P PDC

ATTACMENT Sumary of-Service Water System Investigation and Action Plans The following information describes the condition of the service water system  ;

and future plans concerning service water corrosion control program at River

- Bend Station- (RBS). Recent efforts by Gulf States Utflities (GSU) Company  ;

have determined that the system is capable of performing its required l f functions necessary to support safe operation of RBS.

BACKGROUND-Prior to startup of RBS in December 1985, the service water system was functionally tested using untreated, shallow well water. It was later determined that this water was very aggressive and subseg u ntly led to accelerated corrosion in certain regions of the systems and components.

Excursions of pH and chlorine concentration during initial plant startup have also contributed to the accelerated corrosion observed. The possibility for rapid corrosion was recognized during the first operating cycle and during the first refueling outage from September 15 to December 26, 1987. Pipes, valves and various heat exchangers were examined to evaluate the impact of corrosion on the safety and the performance of various components.

During the first refueling outage and the following operating cycle, i significant system improvements were made. Design modifications and procedural changes in the operation of the clarifier have led to a significant improvement in water quality. The acid injection point in the circulating water flume was moved from close proximity to the service water pumps to a location further upstream to promote better mixing and reduce the quantity of acid being injected into the pumps. Polysilicate corrosion inhibiters were added to the water and were later replaced by a more effective zinc inhibitor. A completely new, automated sodium hypochlorite addition system is being installed during the current refueling outage. In addition to hardware changes, a mobile laboratory facility was brought to the site for continual surveillance of instantaneous corrosion rates, coupon analysis, pH, temperature and conductivity of the circulating water flume. A test coupon rack has also been installed in the service water system between  !

the supply and return headers. The initially high mild steel corrosion rates of approximately 30 mils per year were reduced to 5-10 mils per year at 'the beginning of the current refueling outage.

4 In preparation for the second refueling outage, a program was developed to investigate the condition of the service water system to establish data for future considerations. This program included inspection of the auxiliary  ;

chiller condenser, residual heat building,(coritrol removal building chilled waterRHR), turbine plant closed cooling water (TPCCW

. generator heat exchangers. Additionally, it was planned to clean and coat the service water side of the TPCCW and RHR heat exchangers. Other components such as piping, valves, pumps, and instrumentation were scheduled for inspection when they became available due to maintenance. ]

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t' INVESTIGATION Just before the beginning of the second refueling outage, three pin hole

- leaks were discovered in service water pipes. The corrosion spots were highly localized in the weld or heat affected zone. The appearance of the corroded area indicated the presence of raicrobiologically indr ed corrosion (MIC); however, laboratory results were inconclus!ve. It was also discovered that pin hole leaks had occurred in several piping expansion joints in the weld region joining the stainless steel bellows to their carbon steel flanges. This appears to have been galvanic in nature rather than caused by MIC.

Samples of various corrosion products were ellected and cultures were incubated on site to detect the presence of MIC. Field tests for sulfate reducing bacteria were performed on samples from piping, valves and heat exchangers in the system. Although conditions at the plant in many areas were believed to be conducive for MIC attack, actual occurrences appeared to be infrequent. Until the beginning of the second refueling outage, most of the problems associated with corrosion were related to plugging of small, low flow lines, malfunctioning valves and degradation of heat exchanger performance.

Subsequent to the findings mentioned above, it was deterniined that an expansion of the original program to investigate the condition of the service water system to establish a data base for future consideration would be required. A plan of investigation was developed and implemented for principal areas to be inspected. These areas are: pipe welds, bimetallic joints, valves, heat exchangers, the LSV compressor skid, instrument lines, the fire protection system, and ti.e standby service water cooling tower. A contract was let for offsite laboratory analysis of various samples to be taken. In general, the areas or items in each category were decided upon on ,

the basis of importance to safety, isolation capability (i.e., is an outage requi red) , and impact on plant operation. A summary of the results of the investigation, as well as recommendations for future actions, are discussed below.

GENERAL SYSTEM CONDITION AND TRENDS Primary corrosion mechanisms in the service water system are galvanic couples and concentration cell attack. Occurrence of MIC is infrequent and contributes to only a few percent of the corrosion observed. Further, current chemical addition (e.g., chlorine) practices should keep MIC at a low level.

General corrosion rates have been reduced from 30 mils per year to 5-10 mils per year by improvements in the water treatment program. Further improvements are expected to result from optimization of the program. The extent and rate of pitting corrosion appears to be greatly reduced. This will be confirmed by follow up ultrasonic testing during the next operating .

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Component. operability evaluations were ~ conducted to establish- the local I effects of. the corrosion mechanisms. The results of these evaluations are l' summarized below:

l l 1. piping / Fittings / Welds / Bimetallic Joints: Analysis of the ultrasonic test results shows that. pitting corrosion. may cause minor. leakage. The pitting, which is generally localized, is not a threat to piping integrity, even under worst-case accident loading conditions. Evaluation of the consequences'of the leakage shows no unacceptable consequences.

Repair of pin hole . leaks can usually be accomplished by use of commercially available mechanical devices or by weld overlay.

2. Valves: ?ctam valves were evaluated for their safety significance and the most important valves were, or _will be, tested or inspected and repaired as necessary during the second refueling outage. These valves will be inspected or tested again during the third refueling outage. In particular, the containment isolation valves and the boundary. valves of the . standby service water system will be tested again during the mid-Cycle 3 outage. The safety evaluation included in LER 011 shows that there was no adverse effect as a result of the leakage of the containment isolation valves. Manually operated boundary isolation valves can be closed in a matter of hours should the need arise.

3. Heat Exchangers: A heat exchanger monitoring program is presently in place which includes monthly flow testing to detect adverse trends in heat exchanger performance. A heat transfer monitoring program which will give more direct measurement of heat exchanger perf cmance is under development. However, this program will likely require installation of more accurate instrumentation to be fully effective. During Cycle 2, the monitoring program predicted the need for inspection and repair of a number.of heat exchangers. These inspections and repairs have been completed.

4. LSV Compressor Skid: Cleaning and a partial material upgrade is planned I to begin during the second refueling outage, and be completed by the mid-Cycle' -3 outage. A modification to supply demineralized water to these components is under consideration for installation during the third refueling outage.

5. Standby Cooling Tower: Inspection, by divers, for evidence and extent of corrosion activity has been completed. Some corrosion was noted; however, the general condition of the components in the basin was determined to be acceptable. Only a small layer of sludge, approximately one inch thick, was found at the bottom of the basin. Samples of i corrosion products and the sludge will be analyzed for the presence of MIC. ]

6. Instrument Lines: A monitoring program has been developed to detect plugging of service water instrument lines. This program includes all safety-related and non-safety related instruments which have automatic functions and those which provide remote indication or alarm functions for the operators. A review of past performance indicates corrosion Page 3 of 5

e product plugging can be experienced in approximately a 39 week period.

The identified instruments will be placed on an accelerated 26 week j preventive maintenance program to address this area. j

7. Fire Protection: An inspection was performed on selected areas of the fire protection system to determine the extent of corrosion. Based on visual and UT examination, there were no significant or unusual occurrences of corrosion or corrosion products in the system. The cleanliness of the system is attributed to the following:

a. High pH of the water in the system since all underground piping is concrete lined,

b. Water is clean and free of silt and other materials,

c. Stagnation has probably led to depletion of oxygen and thus, reduced corrosion due to aerobic microbes.

Examination of a threaded connection revealed no evidence of corrosion in this area.

PLANS FOR FURTHER ACTIVITY:

GSU plans further activities to address and correct these conditions. These plans will include the following areas / periods of effort: 1) continued monitoring and examinations to confirm present conclusions and pravide additional data for future use, 2) development of the actions required for final resolution, and 3) final implementation requirements and schedules. In addition to the above, GSU will continue, upon discovery, to address any new conditions which are identified that threaten the operability of the system.

To support these actions, a task force consisting of GSU personnel presently familiar with this area will be established to provide technical direction.

This task force will be supplemented by expert consultants in the fields of corrosion and MIC, as necessary. Gulf States Utilities Company will schedule reports of the findings and progress of these efforts to the NRC at your convenience.  !

For the period from startup from the current refueling outage until the '

mid-Cycle 3 outage, continued monitoring and evaluation will be the primary focus of the corrective action program. These efforts will inclede:

1. Ultrasonic testing of piping,' joints, and fittings will be i continued to verify that current trends and evaluations are correct and adequate. Additional areas will be examined and repeat examinations of identified significant localized corrosion sites will allow further determination of the rate of general and pitting type corrosion.

2. The scope of valve examinations and operability testing will be expanded to include additional testing as valves of interest become available during Cycle 3.

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3. The number of specimens in existing test cocoon racks will ]

be expanded to include items .such as bimetallic welds, weld 1 heat affected zones and pitted specimens. A test-loop, or j shunts, will be designed to test the- effectiveness of {

corrosion softening or corrosion releasing chemicals and to evaluate suitability of various cleaning agents or methods for use at RBS to eliminate the accumulation of corrosion i products, i

4. Components end systenn, examined in this program (e.g., l bimetallic welds, heat exchangers, LSV skid,etc.)will l continue to be monitored to evaluate trends and the effectiveness of the corrosion reduction p"ogram, i

5. As identified above, an expanded preventive maintenance '

program will be implemented on service water i instrumentation. This program will condst of two phases of j implementation. The first phase will be to perform a flow l test of all safety-related instrumentation. This first test j period, including those instruments already in the PM l program. will be completed by September 30, 1989. The l second phase will be to include non-safety related j instrumentation, and will be completed by December 31, 1989.

These programs will continue on a 26 week schedule until a final resolution of this issue is determined.

From the mid-Cycle 3 outage until t'r.e beginning of the third refueling outage, scheduled for September 1990, the final plan to address this issue will be developed. Major efforts of this plan will include an identification of the components which will require repa4

• replacement or cleaning based on.

the data developed from the investigates + identified above. These efforts will be prioritized based on system o, component conditions and plant configuration. In adoition to the above, the information and recommendations of consultants will be evaluated and implemented as appropriate. GSU will advise the NRC of its plans for restoration of the service water system prior to the third refueling outage.

During the period frcm the beginning of the third refueling outage until the completion of the fourth refueling outage, all work identified by GSU as necessary to restore the system to acceptable operating conditions will be implemented.

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