ML20238D642
| ML20238D642 | |
| Person / Time | |
|---|---|
| Site: | Limerick  |
| Issue date: | 09/08/1987 |
| From: | Kowalski S 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 8709110300 | |
| Download: ML20238D642 (8) | |
Text
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PHILADELPHIA ELECTRIC COMPANY 23O1 MARKET STREET P.O. BOX 8699 PHILADELPHIA A. PA.19101 S. J. KOWA LSKI
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Mr. W. T. Russell, Administrator Docket No. 50-353 U.S. Nuclear Regulatory Conmission Region I Attn: Docunent Control Desk Washington, DC 20555 J
Subject:
Limerick Generating Station, Unit 2 Response to I.E. Bulletin E7-01 " Thinning of Pipe Walls at Nuclear Power Pltats"
Reference:
NRC Bulletin No. 87-01 datert 7/9/87
Attachment:
Limer ick Generating Statf ors. Unit 2 Response to NRC 1. E. Bulle';.in No. 87-01 Thinning of Pipe Walls in Nuclear Power Plants Flie:
GOVT 1-1 (Bulletins)
Dear Mr. Russell:
The referenced bulletin requests information regarding utliity programs addressing pipe wall thinning due to erosion / corrosion under single and two phase flow conditions.
Philadelphia Electric's response 1
to the five requested actions is provided in the following attachment.
If further information is required, please do not hesitate to contact us.
Sincerely, 48
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PRB/pdO8218706 Attachment Copy to: Addressee R. A. Granm, Senior Resident inspector U.S. Nuclear Regulatory Corrmission P. O. Box 47 Sanatoga, PA 19464 l
8709110300 070908 PDR ADOCK 05000353 gk G
PDR l
Distribution: S J. Kowalski J. W. Gallagher M. J. Cooney R. H. Logue/W. M. Alden G. M. Leitch M. J, McCormick H. H. Traver l
R. A. Segletes l
T. C. Hinkle L. B. Pyrlh J. M. Madara, Jr.
D. R. Helwig A. R. Diederich D. B. Fetters P. K. Pavlides
7_-
.n ATTACHMENT f
Limerick Generating Station Unit 2 Response to NRC 1.E. Bulletin No. 87-01 Thinning of Pipe Walls In Nuclear Power Plants I
-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 prograns for nonitoring-the wall thickness of pipes in condensate, feedwater, steam,
.and connected high energy piping systenn, including all se.fety-related 4
and non-safety-related piping systems fabricated of carbon steel.
)
in/ormation for Limerick Unit 2 in response to I. E. Bulletin j
87-01 is provided below.
1.
Identify the codes or standards to which the piping was designed and fabricated.
Response
An erosion / corrosion (E/C) Inspection program for Limerick 3
Unit 2, which is still under construction,. will be developed.
Presently, no program exists. The applicable design code for determining the minIntn1 wall requirements will be used after the program scope is defined.
2.
Describe the scope and extent of your programs for ensuring that pipe wall thicknesses are not reduced below the mininom 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 nothods used to nake thickness measurements,
i d.
Making repatr/ replacement decisions.
Response
An insoection progran to address carbon steel piping systems subject to single phase or two phase flow E/C for Linerick Unit 2 wl11 be developed. The basis that will be used for the program development is defined below:
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Two' Phase E/C' A program.to address E/C of. carbon steel piping subject to l
. wet' steam environments will. be developed. ' However, most of
' the;large. diameter piping systems subject' to two phase flow, such as extraction steam,. are fabricated from ' chrome-moly.
materials which exhibit increased E/C. resistance. We plan to-review piping systems uttilzing experience gained from inspections performed at Peach Bottom and fossil stations In' order to' identify the 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 monitor pipe wall thickness for,the Identified suspect systems.
'a.
The piping Inspectton points wt11' include locations'In 3
the system where there are abrupt changes.In.the direction of flow (elbows, tees) Immediately 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 systems wil.1 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 utl112e ultrasonic (UT) thickness measurements supplemented by visual examination where practical.- PECo chose UT because it provides accurate verifiable data, d.
Repalr/ replacement decisions will be based 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-moly materials whenever practical.
Single Phase E/C Piping systems will be selected for inspection based upon review of parameters known to contribute to single phase E/C.
Systems will be initially screened using operating temperature.
1" Those systems operating in the temperature range of high E/C susceptibility will be further evaluated based upon bulk velocities and configuration including the spacing between fittings in the overall system, a.
Inspection point selection will be prima /Ily based upon temperature, bulk velocity and system geometry. The initial step in inspection point selection will be to l
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b rank the systems or subsystems for potential E/C damage using operating conditions. These system data points will be plotted on a graph which relates velocity and temperature to a predicted E/C rate for a given geometry.
l This graph is shown in Figure 1. Pipe geometry factors will be applied to the various components in each system i
to prioritize inspection locations. The final locaticns selected will. represent the highest.ated components for potential E/C damage.
b.
The inspection frequency for subsequent outages will be determined 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 liquid-phase systems, state specifically whether the following factors have been considereci in establishing your criteria for selecting points at which to monitor piping thickness (Item 2a.)
a.
Piping material (e.g. chromium content).
b.
Piping configuration (e.g. fittings less than'10 pipe diameters apart).
c.
pH of water in the system (e.g. pH less than 10).
d.
System temperature (e.g. between 190 and 500F).
e.
Fluid bulk velocity (e.g. greater than 10ft/sec.).
f.
Oxygen content in the system (e.g. oxygen content less than 50 ppb).
Response
1 The evaluation of each parameter listed above for the selection of Inspection locations is discussed belcw:
a.
Piping material composition can have a significant affect on the E/C rate of a component. Most severe E/C damage has occurred in plain carbon steel piping systems.
Small additions of Cr, Cu and Mo can significantly reduce E/C damage of carbon steels. However, it is anticipated that chemical analysis information for the systems to be included In the program for Limerick, Unit 2 will not be available. Therefore, the carbon steel pipe material will be considered identical for all
systen components and will not be used for selecting inspection points within a systen.
b.
Piping configuration is an important fector contributing to the E/C rate. The relationship of piping geometries that produce the greatest turbulence also produce the highest E/C rates.
Pipe canponent geonetry and the spacing between components will be considered within each system to identify and prioritize inspection locations.
J
- c..
Limerick, Unit 2 is a BWR with neutral pH.
As pH levels increase above 9.2, E/C is reduced.
Since pH is constant throughout the systens it will not be considered for inspection point selection.
I d.
Fluid temperature will be considered for rating the pipe j
systems or subsystens in terns of the predicted E/C rate. Temperature versus E/C rate has a peak between 240 to 300F, The ntnber of inspection locations will be j
greater for systems operating in this temperature range.
i e.
Fluid bulk velocity coupled with pipe configuration j
produce turbulent flow. Flow in conjunction with temperature detennine the E/C rate.
Velocity and i
tanperature will be used for ranking the pipe systens.
i Velocity and pipe geanotry wl11 be used for selecting the Inspection locations within a system.
l f.
The oxygen content of the water 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 systems anticipated to be included in the program.,
Therefore, oxygen will not be specifically considered for selecting inspection locations.
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4.
Chronologically list and sunnarize the results of all inspections I
that have been performed, which were specifically conducted l
for the purpose of identifying pipe wall thinning, whether or i
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 j
whether it was specifically Intended to nessure wall i
thickness or whether wall thickness neasurenents were j
an incidental determination.
i b.
Describe what piping was examined and how (e.g. describe l
the inspection instruments, test nethod, reference j
thickness, locations examined, neans for locating measurement points in subsequent inspections.
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c.
Report thickness measurement results end note those that were Identlfled 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 performed a failure analysis, include the results of that analysis.
Indicate whether the actions involve repair or replacement, including any change of materials.
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Response
1 Since Limerick, Unit 2 is under construction, no inspections to detect E/C damage have been performed.
5.
Describe any plans either for revising. the present program or for developing new or additional programs for nonitoring pipe wall thickness.
Response
As stated previously, an E/C program for Limerick, Unit 2 will be developed. We intend to perform the EPRI Chexal-Horowitz-Erosion-Corrosion (CHEC) analysis for single phase E/C.
In addition, we intend to evaltnte findings from other utility inspections for their appilcability to Limerick.
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