ML18150A038
| ML18150A038 | |
| Person / Time | |
|---|---|
| Site: | Surry  |
| Issue date: | 04/16/1987 |
| From: | Stewart W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| 87-108A, NUDOCS 8704220247 | |
| Download: ML18150A038 (20) | |
Text
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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:
.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 l
e 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
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. 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
' r
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
Bearing Cooling Water X
X Secondary Sampling 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 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.
1
- 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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- 1.
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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)
Misc. Drains Secondary Plant
-Equipment condensate drains (excluding traps)
Boron Recovery
-VA system Sampling System
-Steam genefator blowdown Extraction Steam
-11 11 ~nd 2 11 SlED thru S4ED Condensate
-Feedwater heater relief lines Auxiliary Steam
-8 11-SA-13-301
-4 11 -SA-8-301
-3 11 -SA-3-301
-4 11-SA-29,30-301
-ACA & AJA lines Steam Trap Lines
-All 42-WAT-40088-12 Reason for Inspection Exclusion Infrequent use Infrequent use Infrequent use Infrequent use MS superheated condition downstream *of CV Infrequ~nt use Infrequent use Not steam or water Fluid downstream of coolers is less than 150° F.
Carbon steel upstream of coolers is part of Slowdown System inspection program Infrequent use Infrequent use Infrequent use Infrequent use Infrequent use Infrequent use Less than 100° F and at -
atm. or vac. press.
Not considefed a major' operational or safety hazard; to be considered by the ongoing Augmented Inspection Program
Piping Subsystem Auxiliary Steam
-Piping downstream of C.V. 's
-Heating steam piping 42-WAT-AOOBB-13
~
Reason for Inspection Exclusion Low press. and not con-sidered a major operational or safety hazard; to be considered _
by the on-going Augmented Inspeition Program Same as above
e e
In order to validate the stainless steel material exclusions, inspections were done on the Unit 1 charging systems.
Inspections were done on the Unit 1 auxiliary feedwater system to prove the integrity of its piping.
Since no evidence of E;c* was found in the Unit 1 auxiliary feed or charging system; inspections were not done on these systems in Unit 2.
Points were selected within each system in Table 1 based on velocity and geometry with the over:-ri.ding parameter being geometry since the velocities and temperature are relatively constant within each line segment.
Line segments in the condensate and feedwater systems have different temperatures in different locations and inspection points were selected based on geometry and temperature in these systems.
Since there is no previous examination data on single phase liquid flow lines at Surry, a sampling was taken from each system representative of system temperatures and velocities for those areas expected to have significant E/C.
Results from these inspections should provide additional data for correlation of E/C as a function of temperature, velocity and geometry.
Wet steam.system inspection points were selected btsed on the Keller's equation methods presented in EPRI Report NP-3944 entitled "Erosion/Corrosion in Nuclear Plant Steam Piping:
Causes and Inspection Program Guidelines".
This report relates E/C wear rates to temperature, fluid velocity, moisture content and individual components using Keller's equation. -Geometry was a*
separate consideration for compound component configuration, since Keller's equation does not relate the effect of compound geometry to E/C wear rate.
- The applicatibn.of such configurations is left to judgement, with sepa~ation between flow.disturbances being the criteria for severity and ultimate selection.
A minimum of ten pipe diameters is reco1T111ended between flow 42-WAT-40088-14
'* r
e e
disiontinuities. Keller's equation also does not include any influence from changes in water chemistry.
Since no known methods exist.for selection of E/C locations in single phase flow, Technicon developed a rating scheme to identify potentially high E/C wear in single phase flow components a~ follows:
A.
Temperatur~s are considered constant within syst~ms* unless mass flow additions or e.nergy changes cause significant temperature changes.
Any such temperature change was factored into selection of dat,a points.
E/C ratings for various temperature ranges in single pha~e flow were assfgned th~.following values:
Temperature (°F)
Rating 265-320 5
245-265 & 320-350 4
230-245 & 350-380 3
210-230 & 380-410 2
195-210 & 410-440 1
-195 & +440 0
NOTE:
Lines which operate at or near (5°F) saturation should have the above rating value increased by 3~
B.
Velocity effects are compounded by system geometry and in general, flow disturbances caused by other irregularities in the pipe wall.
E/C ratings for velocities were assigned the following values:
Velocity Feet per second (FPS) 42-WAT-40088-15
- 25-30 20-25 15-20 Rating 5
4 3
\\_
10-15 5-10
-5 2
1 0
C.
Piping system geometry was reviewed on a line segment basis considering temperature and velocity, and points were selected for inspection. Consideration was given to high potentia_l E/C areas typical of components such as: Tee's, close coupled fi~tings~, elbows, reducers, pipe downstream of contrQl valves, orifites, check valves, instrument taps, pipe I.D~. weld contours and backing rings.
The characteristics of these components in conjunction with fluid velocity create significant flow disturbances.
These flow disturbances create even higher local velocities and _alter flow -p_atterns thus increasing the degradation rate in these local areas.
. E/C ratings for various geometries and flow disturbances were assigned the following values:
Geometry & Flow Disturbances Control valve, tee (splitting), 180° bend.
Check valves, globe valves, tees (branch), flow
. orifices, components separated 30 d lOD Rating 10 8
90° bends, elbows, reducing elbows 6
Butterfly valves, instrument taps, reducers Gate valves, welds in straight pipe Straight pipe NOTE:
For close coupled geometry 42-WAT-40088-16
( 0 < d < 3 D) combine components by adding rati~g values.
4 2
0
e D = pipe diameter d = distance between components A summation of the numerical values assigned to each category provides a
- relative comparison of the various factors effecting E/C and when placed in numerical order provides a priority for inspection point selection.
The reiults of the inspections being c6nducted will be used to refine the E/C rating model presented above.
Appendix 11 gives summary sheets of the initial primary inspection loc*ations recommended by Technicon with the total rating for E/C of the components.
Additional components in the piping systems were chosen for inspecticin by Virginia Power, including each geometric discontinuity (fittings, piping sweeps, etc.) in the condensate and feedwater systems from the inlet of the 4th J
point heaters to the feed pumps to the,feed regulating valves.
Isometric sketches (-SK drawings) were prepared showing each fitting in all piping systems being inspected.
The sketches assigned a unique component number for each component chosen for inspection.
The initial primary inspection locations recommended by Technicon are labeled by a "P" on the sketches.
Summaries of the UT Inspection data and the acceptance criteria action required for each component is also shown on.each sketch~
The complete set of inspection isometric sketches are attached as Appendix 21 for reference.
- Techni con al so reconmended that vi sua 1 i ns.pecti ons be done on the turbine crossuhder piping and on any piping components that were adjacerit tb any components that were removed or serviced for various reasons.
- A number of the Technicon primary inspection points *identified on the SK drawings were selected at the outset of the project based primarily on piping geometry.
This effort was cqmpleted at the request of the station to direct 1These Appendices are a: part of the Mechanical Engineering Report, ME 0004 and are not included with this submittal 42-WAT-4008B-17
e the inspections that were already underway in the more critical areas of the plant.
Subsequent evaluation of system operation and calculation of line velocities shows that some of these primary points could have been eliminated.
Inspection results confirmed this to be the case.
Using j
model similar to that presented in this report, but updated and-refined to reflect the inspection results, will enhance the primary
- inspection
~
point selection procedure for the ongoing Augmented Inspection Program.
The total number of inspection points for Unit 2 was less than the total for Unit 1. This reduced inspection scope for Unit 2 was a result of knowledge gained from the Unit 1 inspections, which were completed first.
For piping systems exhibiting essentially no E/C wall loss in the Unit 1 inspections (for example the auxilary feed and charging systems), the number of inspection points was reduced in the Unit 2 scope.
However, piping systems shown to have E/C wall loss by the Unit 1 inspections_ were subjected to essentiaily the same number of inspection points in the Unit 2 inspection scope.
. 42-WAT-40088-18
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