IR 05000482/1990020
| ML20043B426 | |
| Person / Time | |
|---|---|
| Site: | Wolf Creek  |
| Issue date: | 05/17/1990 |
| From: | Barnes I, Ellershaw L NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| To: | |
| Shared Package | |
| ML20043B425 | List: |
| References | |
| 50-482-90-20, NUDOCS 9005300018 | |
| Download: ML20043B426 (7) | |
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APPENDIX i
U.S. NUCLEAR REGULATORY COMMISSION
REGION IV
NRC Inspection Report: 50-482/90-20 Operating License: NPF-42 Docket:
50-482 Licensee: Wolf Creek Nuclear Operating Corporation (WCNOC)
P.O. Box 411 Burlington,' Kansas 66839 Facility Name: Wolf Creek Generating Station (WCGS)
Inspection At: WCGS, Burlington, Kansas inspection Conducted: April 16-20, 1990 Inspector:
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[ L. E. Ellershaw, Reactor Inspector, Materials Date and Quality Programs Section, Division of Reactor Safety Approved:
[8-E- / 7 - 9 0 T. Bernes, Chief, Materials and Quality Date Programs Section; Division of Reactor Safety inspection Summary inspection Conducted April 16-20.1990(Report 50t.82/90-20)
Areas inspected: Nonroutine, announced inspection of identified leakage and erosion problems in heat exchanger tubing.
Results: Through wall pitting corrosion of Containment Cooler SGil01A tubing.
was-ascertained by laboratory examination to have probably occurred by an under-deposit corrosion mechanism. An inspector followup item was identified (paragraph 2.4;2) in regard to review of overall licensee actions for long-term
. monitoring and control of corrosion in piping and equipment served by the essential service water (ESW) system. Erosion of diesel generator intercooler tubing is believed to have been caused by increased ESW system flow that resulted from throttling of component cooling water heat exchanger inlet valves during periods when lake water was cold. The licensee is implementing modifications and changes in operating practices which will provide more uniform flow conditions in components served by the ESW system, reduce erosion, and control microbiological 1y induced corrosion in the ESW return lines to the ultimate
heat' sink by diverting a portion of the return flow through the lines during normal' operation.
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9005300016 900522 PDR ADOCK 05000482 Q
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PERSONS CONTACTED WCN0__C
- B. Withers, President and Chief Executive Officer
- J. Bailey, Vice President, Nuclear Operations
- J. Weeks. Manager, Operations
- G. Boyer Plant Manager
- S. Wideman,-Senior Engineering Specialist
- C. Towler, Manager, Instrumentation and Controls
- D.'Jacobs, Supervisor, Engineering
- M. Williams, Manager, Plant Support
- J. Zell, Manager, Training
'R. Logsdon, Manager, Chemistry
- R. Flannigan,_ Manager, Nuclear Safety Engineering
- 0. Maynard, Manager, Regulatory Services
- F. Rhodes, Vice President Engineering and Technical Support
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'*T. Foster, Manager, Modifications 4_
- R. Holloway, Manager, Maintenance and ?iodifications
- T. Moreau, Supervising Instructor
- H. Stubby, Supervisor.-Technical Training
- T. Conleyll, Supervising Instructor. Health Physics Supervisor, Health Physics
- S. Burkdo
- R. Hammond, Health Physicist
- T.=Morrill, Manager, Radiation Protection
- K. Moles, Manager, Emergency and Radiation Services
- B. Reischman, Nuclear Chemist-
- E. Holman, Supervisor, Health Physics
- T. Moore, Radwaste Engineer
- R. Taylor, Supervisor, Health Physics
- J. Stamm, Manager, System Design Engineering
- R. Sims, Supervisor, Equipment Engineering
- J. Pippin, Manager,NuclearPlantEngineering(NPE)
- C, Sprout, Section Manager, NPE-Wolf Creek
- L. Breshears, Supervisor Health Physics
- C, Parry, Director Site Quality
- V. MacTaggart, NPE-Wichita liaison
- R. Benedict, Manager, Quality Control
'*W. Lindsey, Manager. Quality Assurance
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- L. Cook, Supervisor, Supplier Quality J,,,
J. Fletcher, Senior Maintenance Engineering Specialist J. Mehta, Group Manager, Fluid Systems Engineering, NPE-Wichita NRC
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- M. Skow, Senior Resident Inspector
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- Denotes attendance at the exit interview held on April 20,1990.
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The inspector also contacted other licensee personnel during this inspection.
2.
FOLLOWUP ON IDENTIFIED HEAT EXCHANGER PROBLEMS (92701)
During the current refueling outage (Refuel IV), the licensee identified L
tube leakage problems in one of the four containment coolers and tube erosion
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in one of the two diesel generator intercoolers; this leakage necessitated replacement of tubes and tube bundles. The inspector ascertained that there-was a prior history, dating from 1984, of corrosion and erosion problems in
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heat exchangers served by the service water (SW) and ESW systems.
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2.1 Background in March 1984, a high demineralized water makeup to the stator cooling water (SCW) system was identified, which indicated that the system was leaking.
An inspection of the SCW heat exchanger tubes was performed; this resulted in the identification of through-wall )enetration and deep pitting on the inside diameter of the tubes through w11ch the SW flowed. An extensive investigation
wasperformedbyGeneralElectricCompany(equipmentmanufacturer);Bechtel
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Power Corporation (architect / engineer); and EA En Technology, Inc. (biological analysis contractor)gineering, Science, and The results of this
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investigation showed that the tube degradation was characteristic of
microbiological 1y induced corrosion (MIC). Because of the identification of MIC in heat exchangers served by lake water (i.e., SW) and the extensive use of lake water for cooling safety-related and nonsafety-related equipment, management directed that all heat exchanger tubing in contact with lake water he examined visually and by eddy current testing (ET). Certain coolers were
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tested by hydrotest in lieu of ET.
In addition, a program to prevent
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recurrence of HIC based on chlorination of lake water used in the SW system was
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to be developed. The examination resulted in dispositions which included:
use-as-is, tube plugging, retubing, and heat exchan A
chlorinationprogramwasdevelopedbasedonBechtelgerreplacement.
s recommendations that chlorine be injected into the water for 30 minutes every 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> in order to maintain a concentration of at least 0.2 PPM free-residual chlorine as measured at the discharge prior to entry into the lake. The Chemistry Specification Manual WCCH-01 specifies the normal value of free available chlorine to be
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between 0.35 to 0.6 PPM, with an upper limit of 1.0 PPM.
The inspector requested a historical record of work required because of corrosion problems. The provided information indicated that subsequent to the effort described above, no further corrective actions were required until August 1987.
Between August and October 1987, work requests were initiated in on der to replace tube bundles on one diesel generator intercooler and on both diesel
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generator jacket water coolers. The next indication of required work was in
1989 when tubes in the four control room HVAC heat exchangers had to be either plugged or replaced.
It was also noted that one of these same control room
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L HVAC heat exchangers (SGK04B) required additional tube plugging in March 1990
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because of corrosion. The provided printout also listed the containment cooler and diesel generator lube oil cooler problems which are described in more detail in subsequent paragraphs.
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2.2 Containment Cooler At the beginning of Refuel IV and upon entry into containment, licensee personnel observed leakage in Containment Cooler SGN01A. This prompted the
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performance of a hydrostatic test at 150 percent of design pressure on this and the other three containment coolers.
Cooler SGN01A exhibited numerous leaks in 10 of its 12 tube bundles, while the other three containment coolers remained leak-free. Sample tubes (composed of a 90 percent Copper,10 percent Nickel alloy) were removed from one of the tube bundles and sent to two independent laboratories for metallurgical testing and analysis.
It was established that the tube leaks were caused by pitting corrosion. The pits were found to have a one for one association with nodules attached to the inside diameter of the tube. Those tube surfaces with nodules were also covered with a scale.
Analysis showed that the scale and outer surface of the nodules were of the samecomposition(i.e.,highinironandmanganese). The nodules were found to contain a greenish crystalline material, which was identified to be a copper i
salt corrosion product. The pits beneath the nodules were also observed to be dark red in color, indicating the presence of nearly pure copper and that denickelification had been occurring in the corrosion process.
It was additionally noted that some tubes within the same bundle appeared to be free from scale and contained no nodules or pits. A microbiological examination was performed on one tube sample by microscopic examination and culturing of material from deposits and nodules. No microbiological organisms were detected; however,
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these tests could not be performed until several days after the tubing was removed from service.
Based on an engineering evaluation of the analysis data, licensee personnel concluded that the observed tube pitting was most probably the result of r
l under-deposit corrosion. This type of corrosion occurs when available oxygen
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i at a metal surface is reduced due to the formation of a deposit or scale. Low l
oxygen concentration prevents repair of damage sites in passivating oxide films l
onthemetalsurface,whichresultsinthesesites(i.e.,depassivatedareas)
l becoming anodic to the remainder of the metal surface. Because of the very
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smc11 area of the anode (compared to the cathodic area), deep pits result from L
galvanic dissolution of the metal at anode locations. Licensee personnel
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additionally concluded that while biological activity can assist this process, it is not a necessary element for under-deposit corrosion to occur. No specific reasons were identified as to why just one of the four containment coolers leaked. With respect to Cooler SGN01A, 2 tube bundles tmre completely replaced and the leeking tubes in the other 10 bundles individually replaced.
Engineering recommended several corrective actions and preventive measures for control of pitting corrosion in heat exchanger tubing. These recommendations included development of a qualified chemical cleaning method for coolers, cleaning of tubing in other heat exchangers to remove existing scale and deposits, development of an inspection program for monitoring the t
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-5-water side cleanliness of the coo V.s, enhancement of existing inspection programs for monitoring of fouling.nd scaling in heat exchangers, changes in operating practices to eliminate contributory conditions such as periods of low or no flow, and modification of water treatment practices to reduce fouling and scaling. As noted in paragraph 2.4.2 below, the available documentation did not allow a comprehensive determination of the specific actions the licensee is planning to take in response to these recommendations.
2.3 Diesel Generator Heat Exchangers Maintenance and inspection activities, including ET, were planned to be
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performed on the diesel generator heat exchangers during Refuel IV. There are
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three heat exchangers associated with each diesel generator; (i.e.,
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intercooler, lube oil cooler, and jacket water cooler). None of the ;oolers exhibited any leakage. ET examination of the jacket water coolers indicated that all tubes were in an acceptable condition. One tube in one of the luia oil coolers was found to have thinned in excess of 55 percent of the wall avi was plugged. The Admiralty brass tubes in both intercoolers exhibited severe erosion which necessitated the replacement of both tube bundles. After i
I removal of the eroded tube bundles, a number of the tubes were removed and
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sectioned, to allow for visual examination.
it was noted that the worst tube erosion was located at the inlet ends of the tubes.
Further into the tubes, there appeared the normal copper oxide coating, followed by a thin coating of i
l carbonate scale. The inlet spools, end plates, and shell ends had minimal corrosion, with slight pitting in the crevice areas of the end plate flanges.
The outlet shell ends and end plates were completely covered with nodules and a l
layer of corrosion products about 1-inch thick. Removal of some of the l
corrosion layer revealed substantial pitting. Samples of the corrosion l
products were sent to an independent laboratory for analysis. The results were l
not available at the time of this inspection; however, the nuclear chemist l
indicated that previous analysis of corrosion products from these heat
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exchangers showed thtt the products consisted of nearly all iron oxide with some silica and carbonates. The nuclear chemist indicated that the excessive corrosion to the outlet shell ends and end plates was most likely the result of l
flow conditions which allowed the deposition of silt and corrosion products.
It was noted that the outlet pipe spools had minimal corrosion and no pitting.
Increased flow rates through the diesel generator coolers (during periods of cold lake water when component cooling water heat exchanger inlet valves are throttled) are believed to be the root cause of the obarved erosion. The licensee has instituted actions in Plant Modification Request (PMR) 02149 to modify flow conditions. These actions are described in more detail below.
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2.4 Actions Taken by the Licensee 2.4.1 PMR 02149 In~ response to erosion and corrosion problems which have been identified in piping and components served by the ESW system, a major engineering study was undertaken by the licensee which is addressed in PMR 02149. The study was
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,, W-6-completed in July 1989 and resulting planned changes approved for funding in November 1989. Planned changes arising from the study included:
(a) modifications to return a portion of cooling water from each ESW train to ESW system return lines; (b)g normal operation, in order to control MIC in the the ultimate heat sink durin concurrent throttling of SW system return valves to prevent flow increases through ESW system components and valves that occur during periods of cold lake water; (c) ponent water heat exchanger inlet valves as a result of throttling component com installation of additional flow orifices; (d) piping geometry modifications to minimize erosion; (e) installation of chemical injection taps for components with normally low or stagnant flow conditions;and(f)installationofflowinstrumentationacrosstheadditional flow orifices. Certain of these activities are being accomplished during i
Refuel IV; however, the balance have been scheduled for con.pletion during l
Refuel V under a new PMR.
2.4.2 Erosion / Corrosion Control Procedures
Existing procedures noted during the inspection, pertaining to control of erosion / corrosion, were ADM 01-100. Revision 3 "MIC and MIF [Macroinvertebrate Fouling]MonitoringandControlProgram,"andADM08-212, Revision 2,
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" Erosion / Corrosion Monitoring Program." Additional procedures were in development for implementation of Generic Letter 89-13 recommendations.
Full program implementation with respect to Generic Letter 89-13 recommendations is scheduled to be completed by the end of Refuel V.
The available documentation
at the time of the inspection was insufficient to allow a comprehensive determination of the overall long-term actions the licensee is planning to implement with respect to inspection, cleaning, and control of corrosion in piping and equipment served by the ESW system. Review of the licensee's
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program for these activities is considered an inspector followup item.
(482/9020-01)
2.4.3 Alternate Biocides
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i The licensee was noted to have initiated test use prior to Refuel IV of an-l alternate biocide to chlorine. The trial was suspended at the start of
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l Refuel IV, with the initial data not indicating any improvement in biofoul control.
2.5 Sunrnary
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Through wall pitting corrosion of Containment Cooler SGN01A tubing was ascertained by laboratory examination to have occurred by an under-deposit i
corrosion mechanism. An inspector follow up item was identified in regard to review of the licensee's program for inspection, cleaning, and control of corrosion in piping and equipment served by the ESW system. Erosion of diesel generator intercooler tubing is believed to have been caused by increased ESW system flow rates that resulted from throttling of component cooling water heat exchanger inlet valves during periods of cold lake water. The licensee is iriplementing modifications and changes in operating practices which will provide more uniform flow conditions in components served by the essential SW
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i system, reduce crosion, and control MIC in the ESW system return lines to the ultimate heat sink by diverting a portion of the return flow through the lines during normal operation.
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EXIT INTERVIEW An exit interview was conducted on April 20, 1990, with those personnel denoted in paragraph 1.
At the exit interview, the inspectors summarized the inspection findings. No information was presented to the inspector that was identified by the licensee as proprietary.
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