ML20155B577
| ML20155B577 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 09/29/1988 |
| From: | Gridley R TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| TAC-R00468, TAC-R00469, TAC-R00470, TAC-R468, TAC-R469, TAC-R470, NUDOCS 8810060344 | |
| Download: ML20155B577 (10) | |
Text
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TENNESSEE VALLEY AUTHORITY 4
CH ATTANOOGA. TENN!.GSEE 37401 SN 1578 Lookout Place 8EP 291988 l
U.S. Nuclear Regulatory Commission ATTN:
Document Control Desk Mashington, D.C.
20555 Gentlemen
- l In the Matter of
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Docket Nos. 50-259 i
Tennessee Valley Authority
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50-260 j
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50-296 BROWNS FERRY NUCLEAR PLANT (BFN) UNITS 1, 2, AND 3 - MICROBIOLOGICALLY IN00CEO i
CORROSION (MIC) PROGRAM During a recent discussion, the NRC staff requested information on the BFN MIC j
program.
TVA has performed an evaluation to assess MIC at BFN.
Our conclusions are:
(1) the MIC indications which have been found during i.
radiograph examinations have received an engineering evaltation and are j
j acceptable for restart, and (2) if MIC related leakage occurs during 1
operation, the present BFN programs outilned in this submittal will ensure
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adequate evaluations are done for detection and correction of MIC.
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Summary statements i
of comitments contained in this submittal are provided in enclosure 2.
TVA J
will provide a schedule for completion of the first two commitments in l
enclosure 2 by June 1, 1989.
1 If you have any questions, please telephone Clark Madden at (205) 729-2049.
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j Very truly yours, l
TENNESSEE VALLEY AUTHORITY f
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R. GF ley, Man g j
Nuclear Licensing and Regulatory Affairs l
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Enclosures cc:
See page 2 l
5 0910060344 000929 DR ADOCK 000 5,9 g
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i An Equal opportunity Employer
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-2 U.S. Nuclear Regulatory Commission llf 7,$ $@@
cc (Enclosures):
Ms. S. C. Black, Assistant Director for Projects l
TVA Projects Division
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U.S. Nuclear Regulatory Commission One White Flint, North 11555 Rockville Pike Rockville, Maryland 20852 r
Mr. F. R. McCoy, Acting Assistant Olrector
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for Inspection Programs TVA Projects Olvision l
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U.S. Nuclear Regulatory Commission Region II 101 Marietta Street, NN, Suite 2900 Atlanta, Georgia 30323 Browns Ferry Resident Inspector Browns Ferry Nuclear Plant l
Route 12. Box 637 i
Athens Alabama 35611 l
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ENCLOSURE 1 1
BROWNS FERRY NUCLEAR PLANT HICROCI0 LOGICALLY IhDUCEO CORROSION (HIC) PROGRAM l
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BROWNS FERRY NUCLEAR PLANT MICR0810 LOGICALLY INDUCED CORROSION (MIC) PROGRAM i
TABLE OF CONTENTS I
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I.
SLMMRY i
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BACKGROUND l
III.
DETECTION IV.
LEAK DETECTION AND REPAIR V.
CHEMICAL TREATMENT I
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Browns Ferry Nuclear Plant MIC Program I.
SUMMARY
TVA 15 comitted to identifying and controlling MIC at BFN. At 8FN there are three systems in which MIC has been observed.
These are:
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High Pressure Fire Protection / Raw Service Water (HPFP/kSW) 2.
Emergency Equipment Cooling Water (EECW) 3.
Residual Heat Removal Service Water (RHRSW) j A program is being developed at BFN to control MIC in the HPFP/RSW, EECW, and RHRSW systems, and to further monitor the potential structural degradation of the piping in the EECW and RRRSW systems.
This program includes provtsions for detection of MIC bacteria, nondestructive examination (NDE), leak detection, repair, and evaluating use of blocide i
and corrosion inhibitors.
l A major part of the BFN HIC control program will be improved monitoring. Retrievable coupons and in line monitors are planned for Installation in the susceptible systems to provide information on the condition of systems.
In 4ddition, baseline radiography testing (RT) records have been established on 95 stainless steel welds and baseline i
ultrasonic testing (UT) has been performed on carbon steel piping to i
evaluate any future changes. Additional NDE will be performed on a i
population of these unit 2 welds during the next refueling outage.
The observed and measured effects of MIC at BFN has been minimal and has not compromised the operability of the above systems.
II. BAC(GROUND MIC has been identified as a problem at a number of nuclear plants during the past several years.
It is a combination of known corrosion mechanisms accelerated by the by-products of t'acterial activity.
Browns Ferry is committed to addressing identified MIC damage.
The following actions have been taken based on our understanding of MIC effects on these systems, i
A.
Fire Proteccion System I
MIC has been identified as contributing to small random leaks in the HPFP/RSW carbon steel piping.
These laaks which occur infrequently have been in the form of small weeping drips.
The piping in which leaks occurred has been in service since 1977 aad data from ultrasonic testing (UT) inspections have shown that no significant general wall thinning has occurred. Approximately 850 feet of piping has been replaced to repair and mitigate leakage.
The leaks were located primarily in stagnant sections of pipe.
Stagnant and low flow is a prime factor in allowing tubercles and other deposits to develop and create the conditions for under deposit corrosion.
. ^1though deposits have been fcund, flow verification has shown that the system can still deliver required flow and pressure per technical spectftcation (TS) requirements. Additional UT inspect! ors of these sections will be performed to esta511sh the corrosion rate by unit 2 restart.
B.
The EECH System To correct problems with flow restriction in small diameter carbon steel pipe (4 inches or less), portions of the EECH system piping have been replaced with stain 16ss steel piping.
This change has been accomplished during various plant outages since 1978. No leakage due to HIC has been identified in the existing EECW piping i
at Browns Ferry. A UT inspection of two sections of EECH carbon steel piping was conducted in 1984 with no significant general wall thinning found. A baseline RT inspection of 95 stainless steel
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vtids of the total population of 572 stainless steel welds was l
completed in 1987. Only eight EECH butt weids were identified as having small indications of HIC.
The indications found have been evaluated and a reserve factor (RF) has been calculated for the eight welds. The calculations shows the RF for the worst case weld j
is 36.5 percent from its initial condition, and all welds are I
structurally acceptable. The RT inspection conducted was composed of a sampling of EECH stainless steel welds located in all three untts.
The following is a breakdown of tested welds from a total l
population of 572 stainless steel welds that received RT inspection.
I 74 butt welds (15 percent of stainless butt welds) l 21 socket welds (28 percent of stainless socket welds) 95 Total welds (17 percent of W lniess system welds) l To determine the rate that HIC is progressing in the stainless steel welds of the EECit system, the welds identified with HIC and possible HIC indications in the 1987 inspection effort will be re-inspected using RT before unit 2 restart and at each unit outage and/or removed to monitor HIC growth.
In addltion, a population of the unit 2 butt welds which were previously inspected by RT will be re-radiographed before unit 2 restart and at each unit 2 outage to ensure structural integrity of the syttem. Any increase in indications will be re-analyzed to determine any effect on structural Integrity of the system.
At the present time MIC is no*. a problem in the Browns Ferry EECH systems due to the relatively constant flow velocities in the system and the extended chlorination which the sy: tem receives for clam control.
This is consistent with the industry expertence reported I
in the EPRI study "Source Book for HIC in Nuclear Power Plants", as I
well as other technical publications.
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RHRSW System The RHRSW piping is a carbon steel system.
To date, no HIC related leakage or any major indications of MIC have been identified in the RHRSW piping at Browns Ferry.
Random indications characteristic of HIC have been seen during visual and radiographic inspections.
Two such RT indications were evaluated for depth and were found to be within the corrosion allowance for the pipe.and did not violate the code minimum wall thickness requirement.
The indications seen appear on a random basis in the system and are not in singular localized areas.
L lu.f!ON A.
Sampling of Water Systems for MIC Bacteria Samples were taken in 1987 to identify possible bacterial activity in the following systems:
Raw Cooling Water (RCW)
Emergency Equipment Cooling Water (EECW)
Demineralized Water Reactor Building Closed Cooling Water (RBCCW)
High Pressure Fire Protection / Raw Service Water (HPFP/RSW)
Residual Heat Removal Service Water (RHRSW)
Condenser Circulating Water (CCW)
The results of this sampling indicated that the expected iron reducing, oxidizing and pracipitating bacteria as well as fermenting and sulfate reducing bac6eila were present.
The quantitles of bacteria found were not substantially different than baselln? levels found in the supplying river source.
J A sampling program to monitor specif5e plant systems for bacteria o,1 a periodic basis is being developed using plant procedures which will implement engineerli.g requirements.
B.
Installation of Corrosion Monitoring Coupons Retrievable corrosion coupons and in-line monitors are planned for installation to evaluate MIC and control techniques. These monitoring methods will allow a wide variety of test work to proceed without disturbing operations.
Determination of general and l
localized corrosion rates within piping systems may be possible.
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C.
Flow Monitoring The growth of deposits in carbon steel piping have the potential to restrict flow.
The TS has a surveillance requirement on the RHRSH, EECll, and HPFP/RSH systems that verifles the design flow and demonstrates system operability.
In addition to design flow verificetion via surveillance instructions, a detailed flow verification test (Restart Test Procedure 67) is being performed on the EECH as part of the unit 2 restart test program.
Before unit 2 restart, the RHRSH will be tested by a special test (ST 88025) to verify that the system meets design basis flow requirements.
IV.
LEAK DETECTION AND REPAIR Carbon steel develops random pits from MIC damage whila stainless steel is preferentially damaged at welds and heat-affected zones.
TVA corporate studies have established that stainless steel piping can retain a significant margin of structural integrity above FSAR allowables under design basis earthquake conditions even when leaks develop.
The coupon monitoring program will highlight areas which may be subject to MIC or other corrosion attack and help determine the need for additional RT or UT testing, i
Plant Manager Instruction (PMI) 12.12 requires assistant unit operators to look for leakage during their plant walkdowns. Additionally, the ra6 waste inleakage reduction program has an individual assigned full time to inspect for leakage and initiate corrective actions.
Radwaste i
Section Instruction Letter 7 implements the radwaste inleakage reduction i
program and requires a plant walkdown five times a week.
The American Society of Hechanical Engineers (ASME)Section XI required 40 month section hydrostatic test and 10 year system hydrostatic test will also visually detect pipe leakage.
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Fire Protection Leak Detection Leaks are identified during the walkdowns referenced above.
Identified leaks are temporarily repaired using procedure FP-0-000-CHI-01 and a maintenance request is issued for permanent repair. Permanent repair is accomplished during a planned system outage and consists of replacing the affected section of pipe.
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- The TS assures the availability of the fire protection system by imposing surveillance requirements that verify system operability.
The previously identified leakage did not prevent the fire protection system from meeting the system TS hydraulic requirements.
The Browns Ferry FSAR addresses fire protection leakage and states that such leakage will not affect safe shutdown of the plant.
B.
Other System Surveillance Inspections and data from hydrostatic test activities will be used to identify any piping leaks which may develop in the future.
Additionally, the TS strictly imposes surveillance requirement that verify system o?erability.
If pipe leakage occurs which violates BFN TS, the system will be declared inoperable.
V.
CHEMICAL TREATMENT As previously stated in the summary, corrosion inhibitors and biocides are being evaluated for use in MIC affected systems.
Testing is planned to determine the performance of proposed chemicals and their effect.on system components.
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ENCLOSURE 2 BR0HNS FERRY NUCLEAR PLANT MICR0 BIOLOGICALLY INDUCED CORROSION (MIC) PROGRAM List of Commitments 1.
A sampling program to monitor specific plant systems for bacteria on a periodic basis is being developed using plant procedures which will implement engineering requirements.
TVA will provide a schedule for completion of this item in a subsequent letter to NRC by June 1, 1989.
1 2.
Retrievable corrosion coupons and monitors are planned for installation to evaluate MIC and the control techniques.
TVA will provide a schedule for completion of this item in a subsequent letter to NRC by June 1, 1989.
3.
A detailed flow verification test (restart test procedure 67) is being performed on the EECW system as part of the unit 2 restart test program.
4.
Before the unit 2 restart, the RHRSW will be tested by a special test (ST 88025) to verify that the system meets design basis flow requirements.
5.
Additional UT inspections of the HPFP/RSW piping will be performed to establish the corrosion rate by unit 2 restart.
6.
To determine the r&te that MIC is progressing in the stainless steel welds of the EECW system, the welds identified with MIC and possible MIC Indications in the 1987 inspection effort will be re-inspected using RT before unit 2 restart and at each unit outage and/or removed to monitor 1
MIC growth.
In addition, a populi ton of the unit.2 butt welds which were previously inspected by RT will be reradiographed before untt 2 restart j
and at each unit 2 outage to ensure structural integrity of the system.
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