ML20238E850
| ML20238E850 | |
| Person / Time | |
|---|---|
| Site: | Limerick  |
| Issue date: | 09/09/1987 |
| From: | Gallagher J PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC |
| To: | Russell W NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM), NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| References | |
| IEB-87-001, IEB-87-1, NUDOCS 8709150245 | |
| Download: ML20238E850 (12) | |
Text
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.9 PHILADELPHIA ELECTRIC COMPANY 2301 M ARKET STREET
]
P.O BOX 8699 PHILADELPHIA. PA.19101 (215) 841.Sool JOSEPH W. G ALLAGH E ft muc saa oesnAT ons Mr. W. T. Russell, Administrator Docket No. 50-352 U.S. Nuclear Regulatory Conmission l
i Region I l
Attn: Doctment Control Desk Washington, DC 20555
Subject:
Limerick Generating Station, Unit 1 Response to 1.E.Bulletin 87-01 " Thinning of Pipe Walls at Nuclear Power Plants" Mod Request #5613
Reference:
NRC Bulletin No. 87-01 dated 7/9/87
Attachment:
Limerick Generating Station, Unit 1 Response to NRC I. E. Bulletin No. 37-01 Thinning of Pipe Walls in Nuclear Power Plants File:
GOVT 1-1 (Bulletins)
Dear Mr. Russell:
The referenced bulletin requests information regarding utility programs addressing pipe wall thinning due to erosion / corrosion under single and two phase flow conditions. Philadelphia Electric's response to the five requested actions is provided in the following attachment, if further information is required, please do not hesitate to contact us.
Sincerely, PRB/pdO8218706 Attactment 8709150245 070909 PDR ADOCK 05000352 PDR Copy to: Addressee G
E. M. Kelly, Senior Resident inspector
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k U.S. Nuclear Regulatory Conmission P. O. Box 47
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k Ssnatoga, PA 19464
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COMMONWEALTH OF PENNSYLVANIA ss.
' COUNTY OF PHILADELPHIA I
J. W.,Gallagher, being first duly sworn, deposes and says:
s l
i That he is Vice President of Philadelphia Electric Company, the Applicant herein; that he h'as read the foregoing Response to NRC Bulletin 87-01 and knows the contents thereof; and that the statements and matters set forth therein are true and correct to
- the best of hisLknowledge,.information and belief.
w ha v
u Vice President Subscribed and sworn to 9<i-before me this lay of. de4 1987 v
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Notary Public PATNCIA A. JONES Notary Public, PNia., Pr:la. Co.
t#y Commisslon Expires oct 13.1930 e
1
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l ATTACHMENT l
Limerick Generating Station Unit 1 Response to NRC I.E. Bulletin No. 87-01 Thinning of Pipe Walls in Nuclear Power Plants l
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The subject NRC Bulletin was generated as a result of the 1986 Surry feedwater pipe break accident.
Licensees were requested to provide.the following Information concerning their programs for l
monitoring the wall thickness of pipes in condensate, feedwater, l
steam, and connected high energy piping systems, including all safety-related and non-safety-related piping systems fabricated of carbon steel.
Information for Limerick Unit 1 in response to I. E.Bulletin 87-01 is provide below 1.
Identify the codes or standards to which the piping was designed and fabricated.
Response
The Limerick, Unit 1 program is under development.
'The piping systems presently included in the program scope are listed in Table 1.
The appilcable design code for each system is as shown.
2.
Describe the scope and extent of your programs for ensuring that pipe wall thicknesses are not reduced below the minimtm allowable thickness.
Include in the description the criteria that you have established for:
a.
Selecting points at which to make thickness measurements.
b.
Determining how frequently to make thickness measurements, c.
Selecting the methods used to make thickness measurements, d.
Making repatr/ replacement decisions.
Response
The inspection program for Limerick, Unit I will address carbon steel piping systems subject to single phase or two phase flow erosion / corrosion (E/C). Each is addressed separately below:
Two Phase E/C Development of a program to address E/C of carbon steel piping subject to wet steam environments is in progress.
Since Limerick, Unit 1 has completed only one fuel cycle of operation significant E/C damage is not expected.
In addition most of the large diameter piping systems subject to two phase flow such as extraction steam are fabricated from chrome-troly materials. We plan to review piping systems utilizing exparience gained form inspections performed at Peach Bottom and fossil stations in order to identify remaining carbon steel piping potentially affected by E/C damage. The analysis will include review of the system operating parameters and whether there are significant pressure drops which could lead to flashing or cavitation.
Based on this review a program will be developed to nonitor pipe wall thickness for the identifled suspect systems.
a.
The piping inspection points will include locations in the system where there are abrupt changes in the direction of flow (elbows, tees) Irrmediately downstream of significant pressure drops (orifices, control valves) and at other fittings which cause flow perturbations (reducers, branch connections).
b.
The inspection frequency for each of the piping systents w!11 be determined by review of the prior Inspection data. Those systems exhibiting high E/C wear rates will be scheduled for nere frequent inspection.
c.
Inspections will utilize ultrasonic (UT) thickness measurements supplemented by visual examination where practical.
PECo chose UT because it provides accurate verifiable data.
d.
Repair / replacement decisions will be basad upon review of the Inspection data, estimating the erosion rate and comparing it to the design min wall requirements. All piping below code min. wall or anticipated to encroach on min, wall within the next operating cycle will be scheduled for replacement.
Replacements will be made with chrome-rroly materials whenever practical.
l l.
l Single Phase E/C Following the Surry failure PECo developed a progran to detect single phase E/C damage. Piping systens were selected for inspection based upon rev lew of parameters krom to l
contribute to single phase E/C. Systens were initially screened using operating temperature. Those systems operating in the temperature range of high E/C susceptibility were further evaluated based upon bulk velocities and configuration including the spacing between fittings in the overall systen.
A-list of the single phase systens included in the Limerick, Unit 1 program is contained in Table 1.
a.
Inspection point selection was prinerily based upon temperature, bulk velocity and system geonetry. The initial step in inspection point selection was to rank the systens or subsystens for potential E/C danage using operating conditions. These system data points were plotted on a graph which relates velocity and temperature to a predicted E/C rate for a given geanetry. This graph is shown in Figure 1. Pipe goonetry factors were then applied to the various components in each system to prioritize inspection locations. The final locations selected represent the highest rated canponents for potential E/C damage. A total of 26 locations were chosen.
b.
Since no baseline thickness data is available for comparison, we Intend to perform inspections during the next two refueling outages in order to estabilsh E/C wear rates. The inspection frequency for subsequent outages will be detennined based upon evaluation of the inspection data and the estimated wear rates.
c.
This section is identical to the description provided for two phase flow.
d.
This section is identical to the description provided for two phase flow.
3.
For 11guld-phase systens, state specifically whether the following factors have been considered in establishing your criteria for selecting points at which to nonitor piping thickness (Item 2a.)
a.
Piping material (e.g. chromfun content).
b.
Piping configuration (e.g. fittings less than 10 pipe dianeters apart).
c.
pH of water in the system (e.g. pH less than 10).
d.
System temperature (e.g. between 190 and 500F).
-4 e.
Fluid bulk velocity (e.g. greater than 10ft/sec.).
f.
Oxygen content in the system (e.g. oxygen content less
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than 50 ppb).
Response
The evaluation of each paraneter IIsted above in the selection of inspection locations is discussed below; a.
Piping naterial composition can have a significant affect on the E/C rate of a canponent. Most severe E/C danage has occurred in plain carbon steel piping systens.
Sna11 additions of Cr, Cu and Mo can significantly reduce E/C danege of carbon steels. However, specific chemical analysis information for the systems included in the program for Limerick, Unit I was not available.
1 Therefore, the carbon steel pipe noterial was considered Identical for all system components and was not used for selecting inspection points within a system.
b.
Piping configuration is an Important factor contributing to the E/C rate. The relationship cf piping geonetries that produce the greatest turbulence also produce the highest E/C rates. Pipe camponent geonetry and the spacing between canponents was considered within each system to identify and prioritize inspection locations.
c.
Lirerick, Unit 1 is a BWR with neutral pH.
As pH levels increase above 9.2, E/C is reduced.
Since pH was constant throughout the systems evaluated it was not considered for inspection point selection.
d.
Fluid temperature was considered for rating the pipe systens or subsystens in terns of the predicted E/C rate. Temperature versus E/C rate has a peak between 240 to 300F. The nuTber of Inspection locations is greater for systems operating in this temperature range.
e.
Fluid bulk velocity coupled with pipe configuration I
produce turbulent flow.
Flow in conjunction with tanperature determine the E/C rate. Velocity and temperature were used for ranking the pipe systens.
Velocity and pipe geometry were used for selecting the inspection locations within a system.
f.
The oxygen content of the veter strongly affects the E/C rate of carbon steel. The data curves for oxygen content versus E/C rate vary considerably; however, the oxygen levels are relatively constant for the piping systens evaluated; therefore, oxygen was not specifically considered for selecting inspection locations.
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4.
. Chronologically Ilst and sunmarize the. results of all Inspections
.7.
"F that 'have' been perfonned,. which were spect fica 11y conducted ll for the purpose of Identifying pipe wall thinning, whether or l
not pipe wall thinning was discovered, and any other inspections where pipe wall-thinning was discovered even though that was not the purpose of that inspection.
- a. -
Briefly describe the inspection program and Indicate whether it was specifically Intended to measure wall thicknesc or whether wall thickness measurements were an incidental determination.
b.
TDescribe what piping was examined and how (e.g. describe the Inspection Instrtsnents, test mathod, reference thickness, locations excmined, means for locating measurement' points in subsequent Inspections.
c.
Report thickness measurement results and note those that were identified as unacceptable and why.
d.
Describe actions already taken or planned for piping that has.been found to have a nonconforming. wall thickness.
If you have perfonned a failure analysis, include the results of that analysis.
Indicate whether the actions involve repair or replacement, includ!ng any change of materials.
Response
A chronological listing of Inspections performed at timerick, Unit I during the first refueling outage is provided in Table II.
a.
The inspections listed in Table II were specifically Intended to measure wall thickness in response to E/C Concerns.
b.
A description of the piping inspectedz is provided in Table II.
All of the Inspections were performed utilizing manual UT techniques. The inspectors were quallfled in accordance with SNT-TC-1A and the procedures prepared by a quallfled Level III.
The inspection results listed in Table 11 are from single phase flow piping systems. As mentioned previously, the two phase flow inspection program is under development.
Since Limerick, Unit I had only been operating for one fuel cycle, the primary purpose for performing the inspections was to gather basellne thickness data. The single phase examinations are generally performed on
- large diameter lines. Scans are concentrated on inspection bands in regions where E/C damage would most likely occur. The mininun value detected and the thickness range are recorded.
If an crea is found to be below the specIfIed value, the area is mapped, a grid estab1Ished and the min. value located and recorded.
L t.
c.
Thickness measurement results are recorded in Table II.
The specified minim (m wall values are also IIsted.
Measurements thicke - than these specified values are considered acceptable. Those measurements thinner than the specified value will require engineering evaluation.
d.
If the engineering evaluation determines that a code min.-wall violatico is likely during the next operating cycle, replacement of the piping will be scheduled.
Wherever practical, repincements will be trade using 1 1/4 Cr-1/2 Mo mriterial.
5.
Describe any plans either for revising the present program or for developing new or additional programs for tronitoring pipe wall thickness.
Response
The Limerick, Unit 1 E/C program is still under development.
We intend to perform the EPRI Chexal-Horowitz-Erosion-Corrosion (CHEC) analysis for single phase E/C and will amend our program upon evaluation of the results.
In addition, we Intend to evaluate findings from other utility inspections for their applicability to Limerick.
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Feedwater piping" (11-19 feet /sec.)
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Condensate piping (11-15 feet /sec.)
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Feedwater heater drain piping (3-10 feet /sec.)
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Moisture separator crain piping (2-7 feet /sec.)
Piping designed in accordance with ANSI B31.1 1971 Pipe materials are A106 Grade B Fitting materials are A234 Grade WFB
" Portions of system are designed in accordance with ASME Section III Class 1 and 2 1971 Edition with Addenda through Winter 1971.
Class 1 P1pe materials are SA333 Grade 6 Class 1 fitting materials are SA420 Grade WPL Clast 2 Pipe materials are A106 Grade B Clae-2 fitt Ms materials are A234 Grade WPB PRB/pdO8218707 I
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