ML20207K108
| ML20207K108 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 12/31/1986 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20207K105 | List: |
| References | |
| NUDOCS 8701090281 | |
| Download: ML20207K108 (5) | |
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SOUTH TEXAS STATION UNIT 1 SAFETY EVALUATION OF CllMULATIVE USAGE FACTOR CRITERION FOR PIPE RREAK POSTULATION INTRODUCTION The guidance in Standard Review Plan (SRP) 3.6.2, Branch Technical Position ME8 3-1 for postulating pipe breaks in ASME Class I high energy piping can be summarized as follows.
Breaks should be postulated at the following locations:
1.
At teminal ends.
2.
At intermediate locations where the maximum stress intensity range exceeds 80% of the ASME Code allowable stress.
3.
At intermediate locations where the cumulative usage factor (CUF1 exceeds 0.1.
The CUF is an estimate of the percent of fatigue life used up in one plant lifetime. Tht'CUF allowed by the Code is 1.0.
By letters dated March 12, 1986, September 15, 1986, September 17, 1986, October 31, 1986, November 24, 1986, December 8, 1986, and December 15, 1986, Houston Lighting and Power (HL&P) provided technical informaticn to justify the elimination of postulated intermediate bieak locations in Sr,uth Texas Station Unit I wilere the CUF is less than 0.4.
HLAP indicates that by eliminating postulated break locations with a CUF less than 0.4 the number of pipe whip restraints and.iet impingement shields in the South Texas project will be reduced. This action will benefit the South Texas pro.iect because it will reduce the congestier, within the facility, the difficulty of performing plant maintenance, and radiation exposure during inservice inspection.
The letters r.oted above indicated that there are 54 pipe breaks that would be postulated because of calculated CUF values between 0.1 and 0.4.
A summary of these postulated pipe breaks by system is indicated below.
SUWARY OF PIPE BREAK LOCATIONS FOR CUF RETk'EEN 0.1 AND 0.4 System ID No. of Rreaks line Size CUF Ranoe Normal Efiarging to Loop 1 7
4 T to.17 Alt. Charging - Loop 3 4
4
.14 to.26 Aux. Press. Spray 2
2
.12 to.19 Excess Letdown Loop 4 3
2
.12 to.26 Pressurizer Surge 14 16
.10 to.35 Spray Line 2
6
.34 to.39 SI In.icction Loop 1 10 12
.11 to.21 SI Injection Loop 2 10 1)
.11 to.16 SI Infection Loop 3 6
12
.10 to.29 TAPLF 1 8701090281 861231 PDR ADOCK 0500 8
=.
-p-t The piping materials used to fabricate these lines are SA-376 Type 316, SA-312 Types 304L, 304, 316L, and 316, SA-182 Type 316, and SA-403 Types WP 304 and WP 316. The welds in the lines were fabricated using tungsten inert gas, shielded metal arc, and submerged arc processes.
DISCUSSION To support their proposal for the iines in Table 1 except the pressurizer surge line HL&P provided the results of a Westinghouse analysis of a typical accumulator injection line. The CUF calculated for this line was 0.6. The analysis performed was a fatigue crack growth (FCG) analysis with an assumed initial flaw of 5% of the wall thickness. The FCG analysis was performed using the same set of loads and transients as used for the CUF calculations.
The results of a separate FCG analysis for the South Texas pressurizer surge line are contained in WCAP-10489 WCAP-11256, and WCAP-11256 Supplement 1.
The results of the accumulator injection line analysis-were presented in the form of a plot of crack depth versus plant lifetimes starting with an initial crack depth of 5% of the wall thickness. Since the staff does r.ot believe that a 5% flaw would necessarily be detected during preservice inspection, the results were reviewed to detemine the length of time that it would take for a 0.1 to j
0.15 inch deep flaw to grow to an allcwable end-of-life flaw depth.
PLAP also submitted an evaluation of all the sianificaat transients experienced by the pipe lines listed in Table 1 above except the pressurizer I
surge line. This evaluation shewed that the FCG analysis of the accumulator injection line is representative of fatigue crack growth that would be anticipated for the lines in Table 1 except the pressurizer surge line.
The results of both FCG analyses show significantly longer life than would have been estimated based on previously published analysis in other works such as that in NUREG/CR-3059, " Parametric Calculations of Fatigue Crack Growth in Piping." This difference is due to the assumption in the previous work of significantly higher operational stresses, an arbitrary end-of-life flaw depth of 25% of the wall, and use of a more conservative crack growth rate.
The analysis results submitted by HL&P used realistic operational stresses and a fatigue crack growth rate curve based on upper bound data for a PWR environment.
Except for the pressurizer surge ifne, the staff's evaluation is based on an allowable flaw depth calculated according to paragraph IWR-3640 of the ASME Code Section XI for the piping, weld materials, and welding processes used to fabricate these lines. HLAP provided information on the actual weld processes and pipe loads to demonstrate for each line the number of plant lifetimes these lines could be in-service before reaching the flaw depths allowed by paragraph IWB-3640. Except for the 2-inch auxiliary pressurizer spray and excess letdown loop 4 lines at least five plant lifetimes resulted from this evalua-tion.
Five plant lifetimes is considered by the staff to be the minimum acceptable for the type of generalized analyses performed.
, s 1
The FCG analysis of the South Texas pressurizer surce line was.performe'd for the location with the highest CUF for the line. The end-of-life flaw depth was evaluated using techniques similar to those used by IWP-3640. The end-of-life flaw depth was demonstrated to be stable under normal plus safe shutdown earthquake loadings.
HLAP was requested to consider the. effec't of vibratory loadings on fatigue crack growth. Based upon measurements taken durino hot functional testing of recent Westinghouse plants a conservative estimate was made of the maximum displacements and stress levels of the accumulator iniection line. The resulting stress was well below the stresses permitted by ANSI /ASME OM-3-1982.
HL8P will be required to verify that the vibratory stress levels in the South Texa.s applicable to this evaluation are below that required to produce crack growth for crack depths up to those allowed by IWB-3640. This will be treated as a confirmatory item.
Temperature and environment can have an effect en crack initiation and growth.
The oxygen concentration for South Texas Station is specified to be controlled so as not to exceed 0.005 ppm during operation.
In addition all of the piping covered by this safety evaluation is austenitic stainless steel.
Contaminent concentrations are kept below the thresholds known to be conducive to stress corrosion cracking in this piping. The ma.ior water chemistry control standards are included in the plant operating procedures.
For Westinghouse plants there is no history of cracking in the reactor coolant loop piping or in the connecting Class 1 branch piping. Based upon the service history of Westinghouse plants and the primary coolant system chemistry controls that will be in effect at Scuth Texas, the likelihood of stress corrosion cracking is believed to be very low.
The staff has concerns reg)arding the small bore piping (i.e., 6 inches nominal pipe diameter and smaller included in the HL&P proposal. These concerns deal with the applicability of the FCG analysis for small bore piping and the initial flaw sizing capabilities of ultrasonic examination of some of the small bore piping.
CONCLUSIONS We have concluded that the HL&P proposal to not postulate pipe breaks for the SI injection lines and the pressurizer surge line locations indicated by Table 1 is approved pending resolution of the confirmatory item noted above on vibratory stress levels. The staff further concludes that piping 6 inches nominal pipe diameter and smaller should be provided with pipe break protection as required by SRP 3.6.2.
Mr. J. P. Goldberg Houston lighting and Power Company South Texas Project s
cc:
Brian Berwick, Esq.
Resident Inspector / South Texas Assistant Attorney General Project Environnental Protection Division c/o U.S. Nuclear Regulatory Commission P. O. Box 12548 P. O. Box 910 Capitol Station Bay City, Texas 77414 Austin, Texas 78711 Mr. Jonathan Davis Mr. J. T. Westermeir Assistant City Attorney Manager, South Texas Project City of Austin Houston lighting and Power Company P. O. Box 1088 P. O. Box 1700 Austin, Texas 78767 Pouston, Texas 77001 Ms. Pat Coy Mr. P. L. Peterson Citizens Concerned About Nuclear Mr. G. Pokorr,v Power City of Austin 5106 Casa Oro P. O. Box 1088 San Antonio, Texas 78233 Austin, Texas <78767 Mr. Mark R. Wisenberg Mr. J. B. Poston Manager, Nuclear licensing Mr. A. Von Rosenberg Houston lighting and Power Company City Public Service Boad P. O. Box 1700 P. O. Box 1771 Houston, Texas 77001 San Antonio, Texas 78296 Mr. Charles Falligan Jack R. Newman, Esq.
Mr. Burton L. Lex Newman & Poltzinger, P.C.
Bechtel Corporation 1615 L Street, NW P. O. Box 2166 Washington, D.C.
20036 Fouston, Texas 77001 Melbert Schwartz, Jr., Esq.
Mr. E. R. Brooks Baker & Botts Mr. R. l. Range One Shell Plaza Central Power and light Company Houston, Texas 77002 P. O. Box 2122 Corpus Christi, Texas 78403 Mrs. Peggy Buchorn Executive Director Citizens for Equitable Utilities. Inc.
Route 1, Box 1684 Brazoria, Texas 77422 l
o Houston lighting & Power Company South Texas Pro.iect s
CC:
Regional Admin.istrator, Region IV U.S. Nuclear Regulatory Commission Office of Executive Director for Operations 611 Ryan Plaza Drive, Suite 1000 Arlington, Texas 76011 Mr. lanny Sinkin, Counsel for Intervenor Citizens Concerned about Nuclear Power, Inc.
Christic Institute 1324 North Capitol Street Washington, D.C.
20002 licensing Representative Pouston lighting and Power Company Suite 1309 7910 Woodmont Avenue Bethesda, Maryland 20814
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