ML20234B834
| ML20234B834 | |
| Person / Time | |
|---|---|
| Site: | Maine Yankee |
| Issue date: | 09/11/1987 |
| From: | Frizzle C Maine Yankee |
| To: | Russell W NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| References | |
| CDF-87-71, IEB-87-001, IEB-87-1, MN-87-100, NUDOCS 8709210092 | |
| Download: ML20234B834 (11) | |
Text
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r MaineYankee AELIABLE ELECTRICITY FOR MAINE SINCE 1972
~ EDISON DRIVE. AUGUSTA, MAINE 04330. (207) 622-4868 September 11, 1987 MN-87-100 CDF-87-71 i
Region I United States. Nuclear Regulatory Commission 631 Park Avenue King of Prussia, Pennsylvania 19406
- Attention: Mr. Hilliam T. Russell, Regional Administrator
References:
(a)
License No. DPR-36 (Docket No. 50-309)
(b) NRC Bulletin No. 87-01:
Thinning of Pipe Walls in Nuclear Power Plants dated July 9, 1987
Subject:
Response to NRC Bulletin No. 87-01 Gentlemen:.
Attachment I contains Maine Yankee's response to thesinformation requested in Reference (b).
Maine Yankee has, since 1981, had an inspection program to detect.any erosion / corrosion of pipe wall thickness in portions of the condensate, main i
1 steam and feedwater systems.
During the 1987 refueling outage, the main feedwater piping system was closely scrutinized in accordance with this g
program with no evidence of any significant pipe wall loss.
As indicated in the attached, we intend to review the remaining carbon steel piping systems which may be subject to pipe wall thinning for possible inclusion into the existing program.
The review is expected to be completed by the end of the current (Cycle 10) operating Cycle.
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MaineYankee i
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' United States' Nuclear Regulatory Commission Page Two Attention: Mr. Hilliam T. Russell MN-87-100 Please contact us if you have any questions.
Very truly yours, HAINE YANKEE ATOMIC POWER COMPANY C. D. Friz e Vice President and Manager of Operations JBR/bjp I
Attachment:
9 Pages j
cc: Document Control Desk Mr. Cornelius F. Holaen Mr. Pat Sears Mr. Clough Toppan 3
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STATE OF MAINE l
Then personally appeared before me, Charles D. Frizzle, who being duly sworn did state that he is Vice President of Maine Yankee Atomic Power Company, that he is duly authorized to execute and file the foregoing response in the name and on behalf of Maine Yankee Atomic Power Company, and that the statements therein are true to the best of his knowledge and belief.
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V Notary Public E0EY IC MY COMMISSION EXPIRES DCT0eER 3,1H2 4
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Attachment i MN-87-100 MAINE YANKEE ATONIC POWER COMPANY RESPONSE TO NRC PflLLETIN 87-01 NRC Request Hithin 60 days from the receipt of this bulletin, licensees are requested to provide the following information concerning their programs for monitoring the wall thickness of pipes in condensate, feedwater, steam, and connected high energy piping systems, including all safety-related and non-safety-related piping systems fabricated of carbon steel:
1.
Identify'the codes.or'sta'ndards to which the piping was designed and fabricated'.
Maine Yankee Resoonse 1.
The subject piping systems were designed and fabricated in accordance with the 1967 edition of ANSI B31.1 Power Piping Code.
NRC Reauest 2.
Describe the scope and extent of your programs for ensuring that pipe wall thicknesses are not reduced below the minimum 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 replacement / repair decisions l
Maine Yankee Resoonse For two phase systems, areas where the steam / water medium is forced '.o make a sudden change in direction or velocity are selected for examination. These include areas near tees, elbows, orifices, and control l
valves.
For single phase systems, the Cendensate, Feedwater, and Heater Drain Systems were selected based on their similarity to the Surry 2 plant.
l Pipe material, water chemistry (pH), system temperature, fluid velocity, I
and oxygen content were considered.
Examinations were concentrated on l
areas that were subject to turbulence such as near tees, elbows, reducers, and control valves, etc.
l l
The frequency at which an area is monitored is based on the erosion / corrosion rate of the area, once one has been determined. Areas with high erosion / corrosion rates are monitored at least each refueling and sometimes during the cycle while the system is at its normal operation conditions. Areas with slower rates of erosion / corrosion are inonitored less frequently. Areas that have shown wall loss during their first I
examinations are monitored again th'e following refueling to determine if there is a change in the rate of erosion / corrosion.
Two or more measurements of eroded areas are necessary to establish erosion rates and monitoring frequencies.
For those areas which have shown little sign of wall thinning after years of service a small sample size of monitoring points is maintained to ensure erosion rates do not increase significantly.
The methods used for determining wall loss are straight beam ultrasonics and visual observation when the internals of a component are accessible.
The visual method is a quick qualitative method which allows the component to be accepted or rejected without further testing.
Changes in the surface profile and/or magnetite coating indicate areas that should be examined ultrasonically.
The ultrasonic method is a slower, quantitative method that determines the actual wall thicknesses of a component.
These l
measurements are compared to nominal and minimum wall thickness values to l
determine whether or not the component is acceptable for continued service.
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An engineering evaluation is performed based on the components' minimum wall thicknesses as defined by ANSI B31.1 Power Piping Code or.100",
whichever is greater.
If a component's wall thickness is found to be equal to or less than minimum wall thickness or.100", the component is repaired or replaced.
If data analysis shows that a 50% or more reduction in the margin between present wall thickness and minimum wall thickness is likely by the next refueling outage, that component is repaired or replaced.
If the wall thinning of a component is determined to be localized, a 50% or more reduction in the present to minimum wall thickness margin may be deemed acceptable.
If a component is found to be close to minimum wall thickness and no erosion / corrosion rate is available, then for safety purposes, that component will be repaired or replaced.
The following systems are currently included in the inspection program:
a.
Main Feedwater from the pumps discharge to the downstream side feedwater regulating valve stations.
b.
Condensate from the 2nd Pt. Feedwater Heaters to the Main Feedwater pumps.
.c.
First through Fifth Point Extraction Steam from the Turbines to
d.
Main Steam System.
o.
Secondary High Pressure Drain System, f.
HP Skimmer Drains from HP Turbine to drain tank plus vent to second point extraction line.
g.
Feedwater Heater Steam Vents.
h.
High Pressure Heater Drain System.
i.
Low Pressure Heater Drain System.
NRC Recuest 3.
For liquid-phase systems, state specifically whether the following factors have been considered 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., bctween 190 and 500*F) e.
fluid bulk velocity (e.g., greater than 10 ft/s) f.
oxygen content in the system (e.g., oxygen content less than 50 ppb)
Maine Yankee Resoonse See response to Item 2.
NRC Reauest 4.
Chronologically list and summarize the results of all inspections that have been performed, which were specifically conducted for the purpose of identifying pipe wall thinning, whether or 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.
l a.
Briefly describe the inspection program and indicate whether it j
was specifically intended to measure wall thickness or whether
)
wall thickness measurements were an incidental determination.
1 b.
Describe what piping was examined and how (e.g., describe the inspection instrument (s), test method, reference thickness, locations examined, means for locating measurement point (s) in subsequent inspections).
c.
Report thickness measurement results and note those that were identified as unacceptable and why.
j d.
, Des _cribe actions already taken or planned for piping'that has' been found to have a nonconforming wall. thickness.
If you have i
performed a failure analysis, include the results of that analysis.
Indicate whether the actions involve repair or replacement, including any change of materials.
Maine Yankee Resoonse l
4.
Table 1 summarizes the results of past inspections for measuring wall thicknesses.
Straight beam ultrasound was used to measure the wall thickness. A temporary grid pattern was drawn out on each component 1
to depict the scan area.
The entire grid was scanned and the lowest reading in each square was entered on a data sheet with a i
corresponding grid pattern.
From year to year, the grid pattern may not be petitioned in the exact same spot, but since a 1007. scan is done, enough wall thickness data is obtained each time to allow an adequate evaluation of the component's integrity.
Eroded components are usually replaced with either Chrome Holy or Stainless Steel components.
This material substitution has proven to be very effective in reducing the erosion / corrosion rates.
All inspection data is entered into a comprehensive history file to allow for trending.
The history includes graphs which are used to estimate when components will reach their minimum wall limits.
This information allows for early planning for component replacement.
i 1
! 4 NRC Reauest I
5.
Describe any plans either for revising the present or for developing new or additional programs for monitoring pipe wall thickness.
Maine Yankee Resoonse I
5.
Maine Yankee intends to review the remaining carbon steel systems to determine those which may potentially be subject to single or two phase erosion / corrosion.
Those systems shall be added to the existing program and included in future inspections.
He expect to i
complete our review by the end of Cycle 10 operation.
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