e e VIRGINIA ELECTRIC AND POWER COMPANY RICHMOND, VIRGINIA 23261 W. L. STEWART VICE PRESIDENT NYJCLEAR OPERATIONS April 16, 1987 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D. C. 20555 Gentlemen: VIRGINIA ELECTRIC AND POWER COMPANY SURRY POWER STATION UNITS 1 AND 2 FEEDWATER PIPING EXAMINATION AND EVALUATION Serial No. 87-108A NO/WDC:vlh Docket Nos. 50-280 50-281 License Nos. DPR-32 DPR-37 In response to your verbal request for additional information on the feedwater piping inspection program inside containment, the following information is being provided. 1. Identify the inspection points for the feedwater system inside containment and describe the basis for selection of these points. The points inspected on the feedwater system inside containment are as shown on the attached sketches, 11448-SK-13,16,19 and 11548-SK-13,16,19 for Units 1 and 2 respectfully. The criteria for the selection of the inspection locations are described in Tab 6 of our Mechanical Engineering Technical Report, "Determination of the Extent of Erosion/Corrosion in the Secondary and Auxiliary Piping Systems at Surry Power Station," ME-0004, Rev. 1. A copy of Tab 6 is attached. Inspections were expanded, as appropriate, based on the results obtained using the referenced selection criteria. Regarding the specific inspection of the spool piece between the steam generator loop seal and nozzle reducer, the erosion/corrosion rate projected as a result of the inspection of loop B of Unit 2 formed the basis for expanding inspections to the corresponding areas (spool pieces) of other Unit 2 and Unit 1 feedwater lines. 2. How do you account for the higher erosion/corrosion rates found in Unit 2 spool pieces between the steam generator loop seals and nozzle reducers.
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RICHMOND, VIRGINIA 23261 · Mr. Chandu P. Patel NRC Surry Project Manager PWR Project Directorate No. 2 Division of PWR Licensing No. 2 l . e -Tab 6 Mechanical Engineering Technical
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e e VIRGINIA ELECTRIC AND POWER COMPANY
RICHMOND, VIRGINIA 23261
W. L. STEWART
VICE PRESIDENT
NYJCLEAR OPERATIONS
April 16, 1987
U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D. C. 20555
Gentlemen:
VIRGINIA ELECTRIC AND POWER COMPANY SURRY POWER STATION UNITS 1 AND 2 FEEDWATER PIPING EXAMINATION AND EVALUATION
Serial No. 87-108A NO/WDC:vlh Docket Nos. 50-280
50-281 License Nos. DPR-32
DPR-37
In response to your verbal request for additional information on the feedwater piping inspection program inside containment, the following information is being provided.
1. Identify the inspection points for the feedwater system inside containment and describe the basis for selection of these points.
The points inspected on the feedwater system inside containment are as shown on the attached sketches, 11448-SK-13,16,19 and 11548-SK-13,16,19 for Units 1 and 2 respectfully. The criteria for the selection of the inspection locations are described in Tab 6 of our Mechanical Engineering Technical Report, "Determination of the Extent of Erosion/Corrosion in the Secondary and Auxiliary Piping Systems at Surry Power Station," ME-0004, Rev. 1. A copy of Tab 6 is attached. Inspections were expanded, as appropriate, based on the results obtained using the referenced selection criteria. Regarding the specific inspection of the spool piece between the steam generator loop seal and nozzle reducer, the erosion/corrosion rate projected as a result of the inspection of loop B of Unit 2 formed the basis for expanding inspections to the corresponding areas (spool pieces) of other Unit 2 and Unit 1 feedwater lines.
2. How do you account for the higher erosion/corrosion rates found in Unit 2 spool pieces between the steam generator loop seals and nozzle reducers.
e The erosion/corrosion (E/C) rates for the Unit 1 and 2 steam generator feedwater line spool pieces are as shown below:
IA 1B IC
.044"/yr.
.046"/yr.
.036"/yr.
2A 2B 2C
.054"/yr.
.069"/yr.
.048"/yr.
The higher E/C rate found in the Unit 2 B steam generator feedwater line is attributed to piping anomalies and differences in the baseline data used in the E/C rate calculation.
Based on the methodology developed by our independent consultant to identify components which may be susceptible to potentially high E/C rates, the geometry of the Unit 2 B steam generator feedwater line was determined to have a high potential for E/C. In addition, a section of pipe that was nonconcentric was used for the Unit 2 A, B, & C steam generator feedwater line spool pieces following steam generator replacement. Installation of a nonconcentric spool piece at this location may have created more localized turbulence in the line, thus increasing the E/C in the spool piece. As discussed below, it is also likely that the Unit 2 pipe, as originally installed in 1979, had thinner walls than the Unit 1 pipe. As a consequence, these baseline data assumptions could also account for the higher E/C rates observed in each of the Unit 2 lines.
Original installation baseline data were not established for either Unit 1 or 2. For the E/C rate calculations, the steam generator feedwater line baseline data were therefore assumed to be nominal wall thickness plus 10 percent for manufacturer's tolerance (approximately 0.822 inch) with the exception of Unit 2 B feedwater line. For the Unit 2 B feedwater line spool piece the baseline data were assumed to be the maximum wall thickness measured during counterboring procedures (approx .. 835 inch), per Nonconformance Report 79-265. After installation, the spool piece was ground to accommodate radiography. This grinding was not measured and therefore not accounted for when calculating the E/C rate.
The E/C rates were calculated using an assumed baseline values minus the minimum measured thickness (UT) divided by the years of operation. This calculation is assumed to be more conservative for the Unit 2 B steam generator feedwater line spool piece due to the difference in the baseline data (0.835 versus 0.822).
The Unit 2 A and B steam generator feedwater line spool pieces were repaired because of localized wall thinning which resulted in a projected wear life of less than the established acceptance criterion. Wear life is defined as the number of years of operation remaining for a component at its calculated E/C rate with the wall thickness remaining above the minimum code wall requirements. The wear life acceptance criterion is sufficient wall thickness to reach the next refueling outage plus an additional six months for conservatism. For Unit 1, the acceptable wear life was 1 1/2 years and for Unit 2 the wear life was 2 years based on the next scheduled refueling outages. The wear life for the feedwater line spool pieces was calculated by the measured wall thickness minus code minimum wall thickness divided by the E/C rate.
e In summary, the higher E/C rate on the Unit 2 steam generator feedwater line spool pieces is presumed to be due to piping anomalies" associated with the installation of the nonconcentric pipe and the resultant differences in baseline data used in the wear rate calculations.
3. Are there any other areas in the feedwater system for both Unit's 1 and 2 where you would expect to have similar erosion/corrosion rates?
Although the interaction of various parameters (i.e. temperature, alloy content, pH, oxygen content, bulk flow rate, piping geometry, etc) cannot presently be simultaneously related to analytically quantify E/C rates, it has been generally observed that carbon steel single phase flow piping system components in configurations that cause high flow turbulence are susceptible to high E/C rates. As noted above, piping to be inspected was chosen using a methodology which was based on carbon steel piping geometry_ that could result in localized turbulent flow. We have a high level of confidence that the carbon steel piping systems having high potential for E/C have been included in the inspection program.
In addition, we confirmed our inspection methodology assumptions by inspecting several safety related piping systems (i.e. AFW and CVCS) for which we would not expect a susceptability to E/C. No E/C initiated pipe thinning was observed in these inspections. Based on these inspections, we expect the single phase E/C phenomena to be limited to the carbon steel piping of the feedwater system.
If you have any questions, please contact me.
Very truly yours,
~ .. W. L. Stewart
Attachments
cc: U. S, Nuclear Regulatory Commission Region II 101 Marietta Street, N. W. Suite 2900 Atlanta, GA 30323
Mr. W. E. Holland NRC Senior Resident Inspector Surry Power Station
Mr. Chandu P. Patel NRC Surry Project Manager PWR Project Directorate No. 2 Division of PWR Licensing No. 2
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Tab 6
Mechanical Engineering Technical Regort ME-0004
-· Selection of Irispection Locations
in order to determine the extent of E/C in the s~condary side ~nd auxiliary
piping systems, an initial inspection progr~m was developed to recommend·
ultrasonic (UT~ and· visual in'-spection-l~cations. _ Technicon Enterprises, Inc.
(the consultant that prepared Ref~rence 5, EPRI Report - "Erqsion/Corrosion in
Nuc!ear Plant Steam Piping: Causes and Inspection Program Guidelines") was ...
contracted to recommend. the initial inspection locations.
Technicon recQmmended the initial primary inspection locations based on
water chemistry, pipe material, temperature, 'Veloc,ty and pipe geometry.
Systems selected were those steam or water systems which met all of the
following conditions: controlled low oxygen levels, constructed from carbon
steel materials, and operating temperatures greater than .195°F_. This
temperature limit was selected primarily for personnel safety considerations.
Systems having austenitic stainless steel piping are not considered to be
subj~ct t6 E/C attack and therefore, no inspection locations in these systems
were selected by Technico~. No chromium-molybdenum,piping systems were
speci.fied originally for_ the Surry Power Station .
..., A listing of the·piping systems that were selected f,or inspections is given
in Table 1. Table 2 shows a listing of piping systems eliminated from the '
1nspection program and the reason for the elimination. These tables were
generated as a result of a review of the system design data, e.g., flow
diagram~, system descriptions and piping specifications.
After startup of the Units and during development of the-ongoing Augmented
Inspection Program, a more detailed evaluation will b~ conducted of the
velocities and geometric configurations of the carbon steel, water and wet
steam systems listed in Table 2.
42-WAT-4008B-9
e e
. TABLE 1
Piping Systems Inspected for E/C,
Condensate
Feedwater
Main Steam Moisture Separator & H.P. Heater Drains
Steam Generator Slowdown
Flash Evaporator
L. P. Heater Drains
Auxiliary Steam
1st & 2nd Pt. Extraction Steam
3rd & 4th Pt. Extraction Steam
5th & 6th Pt. Extraction Steam
*.A.uxiliary Feed
*Charging
*These systems were not within the scope of recommended inspections, but were
added to the scope of the Unit 1 inspections in order to validate the stainless
steel material exclusion criteria and to eliminate concern over the
functionability of the safety related auxiliary feed system. Since no evidence ·
of E/C was found in the Unit 1 auxiliary feed or charging systems, the scope of
the Unit 2 inspections _did not include t~ese _systems.
42~WAT~4008B-10
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• TABLE 2
Piping Systems Eliminated From Inspection During This Outage - Reason. For Elimination
NOT H(GH LOW CARBON
1 _
02 TEMP STEEL NOT H 0 2
-- --SYSTEM ·Fire Protection X X Domestic ~later X X Fuel Oil X Waste Oil X Circ. Water X X Service Water X X Vacuum Priming X X Chilled Water X X Water Treatment X X Compressed Air X Primary Grade Water X X Turbine Lube Oil X Gland Seal X Electro-Hydraulic Control X Bearing Cooling Water X X Secondary Sampling X Reactor Coolant X Residual Heat Removal X *Chem. & Volume Control X Boron Recovery X Liquid Waste X X
.Decontamination X Gaseous Waste X X Radiation Monitoring X Spent Fuel Pit X X X Reactor Cavity Purification X X X Component Cooling X X Safety Injection X X Containment Spray X X Recirculation Spray X X Primary· Sampling X Containment Vacuum X Primary Vents & Drains X Neutron Shield Cooling X X Condensate Polishing X **Auxiliary Feed X
*This system was added to the scope of the recommended inspections for Unit. in order to validate the stainless steel material exclusion criteria.
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**This system was added to the scope of the recommended inspections for Unit -1 in order to eliminate concern over the functionability of the safety related auxiliary feed system.
42-WAT-4008B-11
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The following carbon steel p1p1ng subsystem operating at 212°F or greater were reviewed and a 1 so exc 1 uded from the. recorrmended scope of inspection for the 1 i sted reasons: ( Reference 22)
Piping Subsystem
Main Steam -SHP line to atmosphere thru
FE-MSlOO -Safety and reliefs -Decay heat release -Main steam dumps · -Turbine stops to cylinder heating
-H 11 SRE 1 i n·e from reheater to crossunder (warm up line)