ML20006B135

Forwards Responses to Generic Ltr 89-13 Re Svc Water Sys Problems Affecting safety-related Equipment.Establishment of Program Revs Prior to Startup from Next Refueling Outage, Scheduled for Fall 1990,planned

ML20006B135
Person / Time
Site:	Vermont Yankee
Issue date:	01/22/1990
From:	Murphy W VERMONT YANKEE NUCLEAR POWER CORP.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
BVY-90-007, BVY-90-7, GL-89-13, NUDOCS 9001310500
Download: ML20006B135 (11)

Text

VE*RMONT YANKEE NUCLEAR POWER CORPORATION 7 Ferry Roao, Brattleboro, VT 05301 7002 BVY 90-007 ENGINE I OFFICE t 140 M AIN STREET BOLToN MA 01740 (500)779 6711 January 22, 1990 U.S. Nuclear Regulatory Commission Washington, D.C. 20556 Attention: Document Control Desk

References:

a) License No. OPR-28 (Docket No. S0-271) b) Letter, USNRC to All Holders of Operating Licenses or Construction Permits for Nuclear Power Plants, NVY 89-156, Generic Letter 89-13, dated 7/18/89 c) EPRI Interim Report, " Heat Exchanger Performance Monitoring Guidelines for Service Water Systems," by N. Stambaugh and W. Closser, dated July 1989 d) Letter, VYNPC to USNRC, BVY 89-76, Additional Response to Maintenance Team Inspection Report, dated 8/11/89

Subject:

Response to Generic Letter 89-13, Service Water System Problems Affecting Safety Related Equipment By letter dated July 18, 1989 (Reference b)], USNRC presented a number of recent operating events and studies that led USNRC to question licensee  ;

compliance with General Design Criteria (GDC) that apply to station Service Water systems. As defined by 10CFR50, Appendix A, the three GDC of concern are: GDC i 44 - Cooling Water GDC 45 - Inspection of Cooling Water Systems and GDC 46 -

Testing of Cooling Water System, as they apply to Service Water systems.

To assure the above issues are being adequately addressed,-Generic Letter 3 89-13 provides a discussion of five recommended actions to be taken by licen-sees. A summary of each of those recommendations and the corresponding Vermont Yankee responses are included in Attachment A. In addition to the programs / practices currently in place to maintain Service Water system perfor-mance, further enhancements are included in Attachment A. These program revi-7 sions will be established prior to startup from the next refueling outage, currently scheduled for the fall of 1990. Per the reporting requirements of ((

this Generic Letter, a letter confirming implementation of these actions will be submitted within 30 days of such implementation, tj Based on the above, Vermont Yankee concludes that it has adequately addressed recommendations I through V of.this Generic Letter to continue to +

. assure the reliability / adequacy of the Service Water system. It should also be noted that this response provides a summary of our present Service Water system In the future, we expect that additional operating experience with efforts.

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i:hese efforts may allow us to refine the practices discussed in this response. -

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9001310500 900122 \ e PDR ADOCK 05000271 .

P PDC

, VERMONT YANKEE NUCLEAR POWER CORPOR ATION U.S. Nuclear Regulatory Commission January 22, 1990 Page 2 We trust that the information contained in this letter is satisfactory however, should you have any questions or require additional information, please do not hesitate to contact us.

Very truly yours, VE MG T YANKEE NUCLEAR P WER CORPORATION

&- ,$ W *'

erren P. %rphy Vice President and Manager of Operations

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/dm cci USNRC Region I Administrator  ;

USNRC Resident Inspector, VYNPS l USNRC Project Manager, VYNPS l

l STATE OF VERMONT)

! )ss WINDHAM COUNTY )

Then personally appeared before n,e, Warren P. Murphy, who, being duly sworn, did stste that he is Vice President and Manager of Operations of Vermont Yankee Nuclear Power Corporation, that he is duly authorized to execute and file the foregoirig document in the name and on the behalf of Vermont Yankee Nuclear Power corporation and that the statements therein are true to the best of his knowledge and belief, b I e m 1. A w Diane M. McCue Notary Public My Commission Expires tebruar 991

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e T ATTACHMENT A l

SUMMARY

OF NRC RECOMMENDED ACTION I For open-cycle Service Watwr systems, implement and maintain an ongoing-program of surveillance and control techniques to significantly reduce the inci-dence of flow blockage events caused by biofouling.

pesoonse-In 1980, Vermont Yankee began an evaluation of the existing condition of the station Service Water system to identify methods for controlling / eliminating biofouling and corrosion of the system piping. This evaluation ef fort included the following actions:

a) Removal of small diameter (2%" and under) pipe samples to determine their condition, b) Internal inspection of large lines and heat exchangers.

c) Analysis of the existing corrosion product composition.

d) Installation of spool pieces and inspection / cleanout ports for system inspection and cleaning.

e) Initiation of an ultrasonic measurement program for surveillance of pipe wall thickness in various Service Water system locations.

f) Establishment of Pipe / Equipment Coating Testing.

Results of the above evaluation effort concluded that the Vermont Yankee Service Water system is susceptible to corrosion and that the corrosion is microbiologically induced by iron bacteria. These bacteria consume the carbon, steel piping material and produce large volume depositions on the pipe wall.

In an effort to control iron bacteria and to maintain acceptable Service.

Water system operation and capabilities, the following programs / practices were.

put into place.

o Service Water Piping Ultrasonic Thickness Measurement Program o Small Bore Pipe Replacement Program o Macroscopic Biological Fouling Species Surveillance I

A discussion of each of these programs / practices is given below.

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1) Service Water Pipino Ultrasonic Thickness Measurement Prooram The Service Water Piping Ultrasonic (U.T.) Thickness Measurement Program was created in 1981 to allow monitoring of corrosion rates in the Service )

j Water system piping at Vermont Yankee.- A previous study had determined j i

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Attachment A Page 2 that system piping corrosion was caused by iron bacteria. The iron bac-teria consume the pipe wall and produce a hydrated iron oxide which has been found to occupy approximately ten times the volume of the original steel. This led to the thinning of pipe walls, the reduction of pipe inside diameter and, in some cases, clogging of small bore Service Water lines.

To quantify this pnenomena, Vermont Yankee initiated this program as part of a long-term coerosion control program. U.T. inspection grids were per-manently identified on Service Water lines at various locations to ensure measurement repeatability. Currently, twenty-seven (27) locations are being measured and evaluated once during each operating cycle. All loca- ,

tions measured are analyzed to ensure pipe minimum wall thickness will be  :

maintained during plant operating life. General measurements have shown  ;

wall thinning to be minor when compared to design code minimum wall j thickness standards. t Ultrasonic thickness testing has shown where the most serious pipe wall thinning / corrosion product build-up has occurred and has allowed the deter-mination of corrosion rates for corrective action determination. The U.T.

testing also allows evaluation of cor-' n control technique effec- ,

tiveness. '

4 The data that has been taken to data .onjunc+ ion with this program has shown that: {

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a) all small bore (2.5" diame' under) lines on the Service Water system needed to be replaceo ensure that flow blockage would not j take place (see discussion of small bore pipe replacement below); and b) large size lines do not need to be replaced because pipe wall thinning has been determined by test results to essentially cease after approximately 0.05" of pipe wall thickness is consumed. Since 3

corrosion product build-up has been found to be approximately ten -

times the thickness of consumed material, a corrosion product build-up of 0.5" is expected in these locations. This has been confirmed by inspection. Since_these lines were originally designed'with excess capacity, this one inch of pipe diameter loss is negligible.

2) Small Bore Pipe Replacement Program 1 As discussed above, the initial phase of the corrosion control program at Vermont Yankee was a study of the corrosion build-up at various locations throughout the Service Water system. Once the corrosion was identified and the required information was gathered, a full scale replacement of small I bore carbon steel Service Water lines was initiated. Since the replacement l of the small bore piping has been completed, only one other location has required replacement due to the potential of clogging. It has been deter-mined by Vermont Yankee that all of the small bore carbon steel Service 3

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a Attachment A Page 3 Water lines that were susceptible to corrosion product build-up have been replaced with either stainless steel or copper piping. Based on the above, it is concluded that flow blockage of small bore lines has.been adequately and completely addressed.

3) Macroscopic Bioloaical Foulino Species Surveillance Vermont Yankee has performed sampling to determine the presence of macroscopic biological fouling species (Asiatic clam) in the Service Water system source. No evidence of this species has been found to date.

To continue to assure the absence of macroscopic fouling organisms,. Vermont Yankee will perform water and substrate sampling annually to detect the presence of both Asiatic clams and Zebra mussels. (NOTE: Per NRC Information Notice No. 89-76, Zebra mussels have recently been found to be populating Great Lakes water sources.) If sampling detects their presence, system chlorination or an equally effective treatment program will be instituted.

SUMMARY

OF NRC RECOMMENDED ACTION II l i

Establish and implement an initial and periodic retest program to verify 1 that safety-related heat exchangers will meet their design / functional require-  !

ments.

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Response

The following is a list of all safety-related heat exchangers that transfer heat to an Ultimate Heat Sink as defined in this Generic Letter.

Residual Heat Removal (RHR) Heat Exchangers IA, 1B Reactor Building Closed Cooling Water Heat Exchangers IA, 18 Diesel Generator Jacket Cooler A, B  ;

Diesel Generator Lube Oil Cooler A, B Diesel Generator After Cooler A, B j RHR Service Water Pump Motor Coolers IA, IB, 1C, ID Reactor Building Recirculation Units (RRU) E. 6,7,8 Cooling Tower #2 Cell #1 In responding to this issue, Vermont Yankee has reviewed an EPRI Interim Report released in July 1989 entitled " Heat Exchanger Performance Monitoring ,

Guidelines for Service Water Systems" [ Reference c)). -This document provides a ~j number of heat exchanger performance monitoring options to assure heat i exchangers will meet their intended safety functions. 4 Vermont Yankee has concluded that the majority of the heat exchangers  !

listed above are already included in existing equipment monitoring programs that  !

coincide with EPRI interim report guidelines. Only the four Reactor Recirculation Units and the four RHR/SW Motor Coolers will need to be added to these programs.

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' Attachment A Page 4 i

A discussion of current and proposed monitoring methods for the subject heat exchangers is given below. This combination of testing, preventive main-tenance, differential pressure monitoring and temperature monitoring will ensure ,

continued equipment capability. '

a) Heat Transfer Method +

The " Heat Transfer Method" of performance monitoring consists of measuring heat exchanger stream temperatures and flows while a substantial heat load is being applied. This data is then used to directly determine heat.

exchanger heat transfer capability. This method is described in more detail in section 4.1 and 5.0 of the EPRI Interim Report (Reference c)].

1. Residual Heat Removal (E-14-1A, IB)

The two RHR heat exchangers were inspected, cleaned and eddy current tested during the 1989 refueling outage. They will be tested by measuring their heat transfer capability as discussed above during'the 1990 refueling outage. This testing will again be performed during the two subsequent refueling outages. Based on this data, a t4ssting frequency will be determined to provide assurance that the design heat r removal capability of these heat exchangers is maintained.

b) Periodic Maintenance Method The " Periodic Maintenance" method of performance monitoring consists of visually inspecting the heat exchangers with the use of a fiber scope or by disassembly. If the visual inspection reveals that fouling is present, the

, heat exchanger is physically cleaned. This method is described in more l

detail in sections 4.5 and 9.0 of the EPRI Interim Report [ Reference c)].

In addition to inspecting and cleaning of the heat exchangers, eddy current testing is performed to identify tube wall thinning.

1. Reactor Building Closed Cooling Water (E-8-1A, IB)

Both RBCCW heat exchaners were eddy current tested and cleaned in 1981, 1985 and 1989. Based on the findings of those inspections, the ,

RBCCW heat exchangers are now scheduled to be cleaned once every

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operating cycle.

2. Diesel Generator Jacket, Lube Oil & After Cooler A, B The Service Water supplied cooling system of each diesel generator is made up of three heat exchangers. 'The three coolers are the Jacket,

Lube Oil and After Coolers. All three coolers in.both diesel genera-l tors have been inspected and eddy current tested. It was determined from these inspections that no significant fouling or corrosion was present and no follow-up cleaning was required.

Attachment A Page 5 To continue to ensure the cleanliness of these heat exchangers, all  ;

six (three per diesel generator) will be inspected and cleaned as necessary when preventive maintenance overhaul is performed on the-diesel generators.

3. Cooling Tower #2 Cell #1 '

Vermont Yankee uses two-eleven cell cross vent cooling towers to cool- .

the Circulating and Service Water systems during the summer months.

• The first cell in-the West Cooling Tower (Cooling Tower #2) is con-sidered to be safety class 2 and is-seismically qualified. Thislis because this cell is part of the Alternate Cooling system, which would '

be used if the normal Service Water system suction source was-lost.

Vermont Yankee visually inspects all of the cooling tower cells on an annual basis. -If required, maintenance is performed at that time.

In addition, the deep basin area under Cooling Tower #2 is visually inspected by divers during every refueling outage. If it is deter-mined necessary, the deep basin is drained and cleaned to remove excess silt. This inspection ensures that the function of the safety class cooling tower cell is maintained.

c) Temperature Monitorino Method 1

The Temperature Monitoring Method consists of monitoring the temperature of the component that is being cooled by the corresponding heat exchanger.

This method is described in more detail in sections 4.3 and 7.0 of the EPRI-Interim Report [ Reference c)].

1. RHR/SW Pump Motor Cooling P8-1A, IB, 10, ID (water / oil)

Performance monitoring of the RHR/SW Pump Motor Coolers will be insti-tuted using the Temperature Monitoring method. -This method will con-sist of monitoring the pump motor temperature during monthly pump surveillances. If the pump motor temperature rises above an appropriate limit, action will be taken. This monitoring program will  ;

be initiated prior to the end of the,next refueling outage, j d) Delta P Method j i

The Delta P Method, as described in section 4.2 and 6.0 of the EPRI Interim i Report (Reference c)] allows monitoring of heat exchanger fouling. l Monitoring is accomplished by correlating heat exchanger flow rates and '

corresponding pressure drops, i l

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Attachment A Page 6

1. Reactor Recirculation Units 5, 6, 7, 8 (water / air)

The performance of the four safety-related RRU units that cool.the RHR  ;

corner rooms will be evaluated by measuring the inlet and outlet pressures as well as the Service Water flow rate. If the flow rate and pressures are comparable to the design values, the unit will be considered to be free of fouling. This monitoring program will be initiated prior to end of the next refueling outage,. which is currently scheduled for the fall of 1990. 7 e) Closed Cvele Heat Exchanoers At Vermont Yankee, closed cooling water systems are chemically treated to prevent corrosion of system components. The chemicals consist of either molybdate-based caustic passivators or filming-type corrosion inhibitors.

The adequacy of this treatment program was recently evaluated as part of an internal INPO commitment. The treatment of these systems currently meets or exceeds industry standards and vendor recommendations. No changes in closed cooling water chemical treatment programs. are necessary.

SUMMARY

OF NRC RECOMMENDED ACTION III Establish a routine inspection and maintenance program 'which will ensure that the performance of safety-related systems serviced by the SW system will not degrade due to corrosion, erosion, protective coating failure, silting and biofouling in the SW system. Maintenance should include at.least the removal of excessive accumulations of biofouling agents,. corrosion products and silt and the repair of defective coatings and corroded parts which may affect safety system performance. ,

Response

A number of programs are currently in place at Vermont Yankee that actively-pursue the identification and repair / resolution of the concerns listed in this item. As discussed in the response to Recommended Action I above,- piping corro-sion concerns have been thoroughly addressed by small bore piping replacement and the ongoing pipe wall thickness surveillance program. The biofouling issue has also been addressed by that program and by the heat exchanger maintenance /

monitoring methods described in the response to Recommended Action II.

To further assure Service Water system reliability, the following main-tenance programs / practices are currently.in place at Vermont Yankee.

a) Check Valve Preventive Maintenance Proaram This program was internally initiated and then further refined to include input from INPO SOER 86-03, " Check Valve Failures and Degradations".

' Service Water system check valves identified in the program are totally disassembled and inspected per a visual inspection checklist. -This-checklist allows documentation and evaluation of numerous items important

Attachment A Page 7 i

I to proper check valve operation. These items include, but are not limited to, valve body and seat condition, disc condition, hinge pin diameter and condition. All check valves in this program are then refurbished, as required, after inspection. Inspection results are used to establish future inspection frequency.

b) Heat Exchanaer Eddy Current Testina Program This program covers inspection of Service Water system heat exchanger tubing for evidence of pitting, erosion, corrosion, and excessive sludge build-up. Tubing is then mechanically cleaned and deposits removed. After each inspection, an evaluation is performed using the data obtained and past inspection results to validate / revise the inspection frequency.

c) Service Water Intake Structure Cleanino The structure and traveling screen filtration' systems are inspected by divers once per operating cycle. Any debris or obstructions are removed to assure a reliable Service Water pump suction path, d) Service Water Pump Maintenance Each of the four Service Water pumps is inspected and overhauled on a bien-nial basis. In addition, all pumps are tested on a monthly basis per the-ASME Section XI Inservice Testing Program.

e) Service Water Strainer Maintenance Strainers on the Service Water pump discharge are monitored for changes in differential pressure and are cleaned as indicated by those changes, f) Service Water Valve Inspection Procram The Service Water Valve Inspection Program was initiated.in 1982 and is being further refined by Vermont Yankee. During the 1990 refueling outage, this program will institute a long-range schedule for taking Service Water.

valves out of service, disassembling the valves for inspection and repairing as required. It should be noted that protective coatings have been applied to a small number-of Service Water system valves and their condition is being monitored via the Valve Inspection Program. Protective coatings are not in use in Vermont Yankee safety class Service Water piping.

In addition to the above, locations in the Service Water system that may be susceptiole to erosion and siiting will be identified as described in the <

response to Recommended Action IV below. Appropriate inspection of these loca-tions will then be performed so that corrective action can be taken. .

Attachment A- >

Page 8

SUMMARY

OF NRC RECOMMENDED ACTION IV Confirm that the as-built SW system meets its design requirements'and w'ill perform its intended function in accordance with the applicable licensing basis of the plant; including confirmation of its ability to perform its-required safety function in the event of a single active component failure.

Response

Through the Design Change process, Vermont Yankee adequately maintains the Plant Licensing Basis as set forth in the Final Safety Analysis Report, Technical Specifications, and the Design Basis Manual. Implicit in this process is the evaluation of single active component failures. ~To further ensure the functional adequacy of the Service Water system, a computerized system flow model is being developed. This model will also be used to determine system locations susceptible to erosion or silting based on fluid stream velocities.-

Based on an evaluation of the results from the completed flow model, an action plan addressing any further efforts needed on this issue will be developed in the fall of 1990 with an appropriate schedule.

SUMMARY

OF NRC RECOMMENDED ACTION V Establish and implement maintenance practices, operating procedures and effective training programs which will ensure that safety-related equipment cooled by the SW system will perform its intended function and-that plant staff responsible for this equipment will reduce the-incidence of human errors- that-frequently occur in the operation, repair and maintenance of SW systems.

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Response

At Vermont Yankee, the~ maintenance and operation'of the Service Water-system is closely controlled by operating and surveillance procedures. All of i

these procedures are required to be comprehensively reviewed on a biennial basis. At a minimum, this biennial review includes:

a) a review of all procedure steps; b) verification of references; and c) identification of the impact of any proposed changes in other procedures. '

! Based on the above, Vermont Yankee believes that the procedures that control the maintenance and operation of the Service Water system are adequately

reviewed. Procedure changes required to' implement responses given to this 1

Generic Letter will be in place prior to the end of the 1990 refueling outage.

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E j Attachment A ,

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In addition, plant operations personnel have received enhanced training on l

the issues raised by this Generic Letter. This training promoted an increased I

awareness of Service Water system susceptibilities as discussed in the NRC Recommended Actions and the programs and practices in place at Vermont Yankee to >

address them. This training was completed in the fall of'1989.

As described in Reference d), Vermont' Yankee has recently developed a main-tenance program document to assure that good maintenance activities continue in I the future for all plant equipment. This document is intended to establish additional maintenance programmatic controls and to formalize current main-tenance good practices. '

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