ML17221A394

Forwards Response to NRC Bulletin 87-001, Thinning of Pipe Walls in Nuclear Power Plants. Scope & Extent of Program Includes All Moderate & High Energy Carbon Steel Piping Sys, Both Nuclear safety-related & nonsafety-related

ML17221A394
Person / Time
Site:	Saint Lucie
Issue date:	09/10/1987
From:	Woody C FLORIDA POWER & LIGHT CO.
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
Shared Package
ML17221A395	List: ML17221A394 ML17221A396
References
IEB-87-001, IEB-87-1, L-87-376, NUDOCS 8709160129
Download: ML17221A394 (9)

Text

REGULATOR INFORMATION DISTRIBUTION, 'EM (RIDS)

ACCESSION NBR 8709160129 DQC. DATE: 87/09/10 NOTARIZED: YES DOCKET FACIL: 50-..335 St. Lucie Planti Unit ii Florida PoUJer h Light Co. 05000335 50-389 St. Lucie Planti Unit 2i Florida Poeer 5 Light Co. 05000389 AUTH. NAME AUTHOR AFFILIATION WOODY) C. O. Flor ida Power h Light Co.

REC IP. NAME RECIPIENT AFFILIATION Document Control Branch (Document Control Desk)

SUBJECT:

Foreard s response to NRC Hul le tin 87-001'Thinning of Pipe Walls in Nuclear Poeer Plants. " Scope 5 extent of program includes all moderate 5 high energy carbon steel piping sgsi both nuclear saf et'-related 5 nonsa f etg-related.

DISTRIBUTION CODE: IE11D COPIES RECEIVED: LTR TITLE: Bulletin Response (50 DKT)

L ENCL + SIZE:7 +

NOTES RECIPIENT COPIES RECIPIENT COPIES'TTR ID CODE/NAME LTTR ENCL ID CODE/NAME ENCL PD2-2 LA 0 PD2-2 PD 1 1 TOUR I GNY> E 1 INTERNAL: AEOD/DOA 1 1 AEOD/DSP 1 AEOD/DSP/TPAB 1 1 NRR/DEST/ADE 1 NRR/DEST/ADS 1 1 NRR/DEBT/MEB 1 1 NRR/DOE*/EAB 1 1 NRR/DOEA/GCB 1 1 NRR/ /EPB 1 . 1 NRR/PMAS/ ILRB 1 1 E FILE 02 1 1 RES/DE/EIB 1 1 RG 2 FILE 01 1 1 EXTERNAL'PDR 1 NRC PDR NSIC 1 1 TOTAL NUMBER OF CQP I ES REQUIRED: LTTR 19 ENCL 18

P. O. BOX 14000, JUNO BEACH, FL 33408 0420

.0 SEPTEtiIBXR 1 0 1987 L-87-376 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D. C. 20555 Gentlemen:

Re: St. Lvcie Units I and 2 Docket Nos. 50-335 and 50-389 NRC Bulletin NO. 87-0 I Thinnin of Pi e Walls in Nuclear Power Plants By the subject Bulletin, the NRC staff requested information concerning programs for monitoring the wall thickness of pipes in condensate, feedwater, steam, and connected high-energy piping systems.

Attached is the response to this Bulletin for St. Lvcie Units I and 2.

The attached information is provided pursuant to Section I82a of the Atomic Energy Act of l954, as amended. If further information is required on this topic, please contact us.

Very truly yours, C. O. Woo Group Vi resident Nuclear Energy COW/E JW/gp Attachments cc: Dr. J. Nelson Grace, Regional Administrator, Region II, USNRC Senior Resident Inspector, USNRC, St. Lucie Plant 8709160229 870910 PDR ADQCK 05000335 8 PDR an FPL Group company

, E JW3/038/I

0 ~l ~ l STATE OF FLORIDA )

) ss.

COUNTY OF PALM BEACH )

~C.O.W That he is d 1 i fi d l,d

'a Grou Vice President d

of Florida Power & Light Company, the Licensee herein; That he has executed the foregoing document; that the statements made in this document are true and correct to the best of his knowledge, information, and belief, and that he is authorized to execute the document on behalf of said Licensee.

C. O. Woody Subscribed and worn to before me this g,day of , 19~.

NOTARY PUBLIC, in and for the County of Palm Beach, State of Florida

>> ~OB~EC $ Z)g

'.'ORE) g 1 1

~offqgS>0 My Commission expires: ~0'tf<> 4av jaj>>, ,. '"'

NRC BULLETIN 87 THINNING OF PIPE lVALLS IN NUCLEAR POPOVER PLANTS Information Re uest 1:

Ideptify codes or standards to which the piping was designed and fabricated.

~Res ense 1 St. Lucie Unit 1 Non-nuclear safety related piping: ANSI B31.1.

Nuclear safety related piping: ANSI B31.7.

St. Lucie Unit 2 Non-nuclear safety related piping: ANSI B31.1.

Nuclear safety related piping: ASME Section III.

Information Re uest 2 Describe the scope and extent of your programs for ensuring that pipe wall thicknesses are not below the minimum allowable thickness. Include in the description the criteria you have established for:

A. Selecting points at which to make thickness measurements.

B. Determine how frequently to make measurements, C. Selecting methods used to make thickness measurements.

D. Making repair/replacement decisions.

~Res onse 2 St. Lucie Unit 1 R 2 In general, the scope and extent of the St. Lucie program includes all moderate and high energy (i.e., above 200oF) carbon steel piping systems, both nuclear safety related and non-nuclear safety related. Inspection locations are established in accordance with accepted industry methods such as those provided by EPRI for single and two phase systems. within specific piping systems, locations for inspections are selected based upon such factors as fluid velocity, piping geometry, moisture content (for steam) and chemistry. Areas which are subjected to flow disturbances such as elbows, branch connections, piping and fittings downstream of control valves or flow orifices are preferred locations for inspections.

Pg. 2 Res onse 2 (cont'd)

Frequency of inspection is based upon the rate of erosion/corrosion. Each operating cycle, inspection data is reviewed to determine which locations, based upon measured maximum erosion/corrosion rates, may be approaching code minimum wall thickness values. Locations which may violate code minimum wall thickness within the next operating cycle require corrective action.

The method of examination is selected based upon the ability to accurately'rovide a profile of wall thickness readings over the entire area of the piping or fitting expected to experience significant erosion/corrosion. In general, ultrasonic devices have been used for this purpose.

Decisions to take corrective action for piping and fittings which have suffered erosion/corrosion damage are based upon the ability of the piping or fitting to satisfy code minimum wall thickness requirements during the subsequent operating cycle. If the lowest wall thickness reading in a piping section subtracted from the erosion/corrosion expected during the subsequent operating cycles is less than the minimum value required by the applicable code, the piping section must be repaired or replaced.

Information Re uest 3 For liquid-phase systems, state specifically whether the following factors have been considered in'stablishing your criteria for selecting points at which to monitor piping thickness:

A. Piping material B. Piping configuration C. pH of water in the system D. System temperature E. Fluid bulk velocity F. Oxygen content

~Res onse 3 St. Lucie Units I 2 2 The initial 'single-phase inspection programs for St. Lucie Units I R 2 were developed soon after the Surry pipe rupture incident. The major factors used to select inspection locations were similar to those accepted for two-phase flow systems and included material composition, temperature, flow path geometry, fluid velocity, fluid pH and oxygen content. Inspection planning tools such as EPRI's "CHEC" Computer Program for single-phase erosion/corrosion were not available during initial St. Lucie single-phase systems such as feedwater, heater drain, condensate and blowdown. within these systems, geometry was considered the most important selection factor. Closely spaced fittings, branch connections, elbows and piping/fittings downstream of control valves were given highest priority for inspections.

Pg. 3 Information Re uest 0 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.

A. Briefly describe the inspection program and indicate whether it was specifically intended to measure wall thickness or whether wall thickness meausrements were an incidental determination.

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.

1 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.

St. Lucie Unit 1 During the 1983 refueling outage, the turbine cross under piping was inspected for wall thickness loss. The results are contained in Attachment D.

As a result of the Surry incident and general concerns regarding erosion/corrosion in two-phase systems, a comprehensive inspection program was developed. The program was specifically intended to collect data on the wall thickness profiles of several high energy pipe(fittings to detect erosion/corrosion degradation. For two-phase systems such as extraction steam, an EPRI methodology (EPRI HP-3900) for predicting erosion/corrosion rates was utilized. For single-phase systems, such factors as flow geometry, temperature, fluid chemistry as previously discussed were utilized in selecting inspection points. The program was designed to first

'inspect the most likely points for erosion/corrosion and to collect "baseline" data on other locations, with program expansion required if wall thinning in any location was more severe than anticipated.

Ultrasonic examination was used to determine wall thickness. "Zone maps", as shown in the attachments, were used to specify the extent of examination required at each selected inspection point. The ultrasonic probes were moved along each circumferential line of the zone map, the data was fed to a strip chart recorder.

The ultrasonic instrumentation was of the pulse echo-type with cathode ray tube display. Carbon steel incremental step blocks were utilized to provide reference thickness to calibrate the instrumentation.

Res onse 0 (cont'd)

A total of 52 locations were selected based on anticipated erosion/corrosion rates; of these,02 locations were in the extraction steam systems, and 10 locations were in single-phase systems. For each of these locations, a "screening criteria" was provided to indicate when engineering evaluation of the thinning was required. The screening criteria was conservatively defined as the minimum wall thickness for the piping plus the maximum possible erosion/corrosion which could occur during the subsequent cycle of operation. A copy of the inspection program document is provided as Attachment A.

The 1987 refueling outage inspections revealed that significant erosion/corrosion degradation was limited to the extraction steam piping and the moisture separator reheater shell side drains. In the case of the extraction steam systems, and piping segments required replacement. All measurements in single-several'itting phase piping systems revealed that the piping is all still within manufactureres tolerances for wall thickness (i.e., nominal wall thickness plus or minus 12'%).

Based on single-phase piping inspection results, erosion/corrosion rates appear to be very low, and encroachment on minimum wall thickness values is not expected for several operating cycles. Attachment B is a summary report which provides the results of all Unit 1 wall thickness inspections and describes corrective actions which were required.

St. Lucie Unit 2 St. Lucie Unit 2 has been operating for less than half the time that St. Lucie Unit 1 has operated. Since the plants are virtually identical in terms of configuration and erosion/corrosion parameters, pipe wall thinning location-for-location is expected to be generally 50% or less of the Unit 1 values. A program has been developed for Unit 2 which is modeled after the Unit 1 program. Inspection points have been selected based upon Unit 1 inspection results. The first Unit 2 wall thickness measurements to detect erosion/corrosion will be conducted during the 1987 refueling outage in October and November. Attachment C is a copy of the Unit 2 inspection program document.

Information Re uest 5 Describe any plans either for revising the present or for developing new or additional programs for monitoring pipe wall thickness.

~Res ense 5 St. Lucie Units 1 R 2 Florida Power R Light Compan'y is satisfied with the program as a whole and in particular the inspection method. The "ultrasonic zone mapping" technique proved adequate in providing the information necessary to make sound decisions on corrective actions. The methods for determining "screening values" are logical and ensure that code requirements for minimum wall thickness are satisfied.

MCI1:5

Pg.5 St. Lucie Units 1 R 1 (cont'd)

IVith respect to selection criteria, the EPRI methodology for two-.phase erosion/corrosion proved to be an excellent tool for determining, on a relative basis, where to concentrate inspection resources.

Future program inprovement is expected in the single-phase inspection location selection technique. Future programs (beginning with the 1988 Unit 1 inspection) will have single-phase locations selected with assistance from EPRPs "CHEC" computer program. This program will provide a prioritized selection of inspection points based on consideration of piping material, flow rates, configuration, water chemistry, etc.. In addition, we will continue to monitor the inspection results from the nuclear industry, particularly in the single-phase flow areas.

Modifications to the inspection program will be made to reflect new findings elsewhere as considered appropriate.

MCI1:5