ML20136F608
| ML20136F608 | |
| Person / Time | |
|---|---|
| Site: | Saint Lucie  |
| Issue date: | 08/09/1995 |
| From: | NRC |
| To: | |
| Shared Package | |
| ML20136C539 | List:
|
| References | |
| FOIA-96-485 NUDOCS 9703170013 | |
| Download: ML20136F608 (7) | |
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION
<2 4 ON THE FLORIDA POWER AND LIGHT COMPANY'S SUBMITTAL DATED 3/2/1995 l
MATERIAL INTEGRITY SECTION j.
MATERIALS AND CHEMICAL ~ ENGINEERING BRANCH ji DIVISION OF ENGINEERING
1.0 INTRODUCTION
I On March 2, 1995 Florida Power and Light Company (the licensee) submitted.in j
a report, for NRC approval, its fracture mechanics evaluation of St. Lucie pressurizer instrument nozzles [1].
In subsequent response to staffs request l.
for additional information (RAI), the licensee forwarded to the NRC its
['7 response to RAI [2] on July 7, 1995 and Revision 1 [3] of the report on August
-2, 1995. These reports are updates of the submittal [4] dated March 28, 1994, which was approved by the NRC on April 1, 1994.
IWB-3132 of Section XI of the 1]
Boiler and Pressure Vessel Code of the American Society of Mechanical. -
<9 Engineers (ASME) Code states that, components with flaw indications shall be i
acceptable for service without the flaw removal, repair, or replacement if an analytical evaluation, as described in IW8-3600, meets the acceptance criteria of IWB-3600. Using IW8-3600, the licensee's contractor made some very 4
conservative assumptions in its 1994 flaw evaluation to gain approval for one fuel cycle. The current submittal by the licensee was developed by a new contractor,. Babcock and Wilcox Nuclear Technologies (BWNT) and is intended to gain approval for 30-year plant life, using more realistic assumptions and employing the finite element method (FEM) in the analytical evaluation of the 4
i pressurizer instrument nozzles flaws. A proposed inservice examination plan l-in accordance with IWB-2420 (b) and (c) is also included in this report.
2.0 BACKGROUND
i' During the 1994 refueling outage, the licensee found boric acid leakage from l
the "C" instrument nozzle in the pressurizer upper head of St. Lucie Unit 2.
Subsequent nondestructive examination detected indications in two other i.]
similar instrument nozzles. To prevent further leakage, the licensee repaired i
all four nozzles by welding Inconel 690 pads to the nozzles at the outside surface of the pressurizer head. Also, to justify. restart without removing and repairing the nozzle flaw at the inside surface of the pressurizer head, i
the licensee submitted a flaw evaluation in accordance with IWB-3600. This l
submittal was approved by the NRC on April 1, 1994. Current submittals, 32-1235127-00, -01, and -02, and 32-1235128-00, -01, and -02 for St. Lucie 2 pressurizer instrument nozzles, can be considered as updates of the 1994 report.
3.0 EVALUATION The current analysis submitted by the licensee used the characterization of the pressurizer instrument nozzles flaw reported in the approved 1994 Attachment l
1 9703170013 970301 PDR FOIA 4
BINDER 96-485 PDR a
y 2
i submittal. The assumed flaw depth of 0.875 inches from the flaw characterization was equal to the weld depth including the butter and is 4
considered reasonable by the staff. Methods and acceptance criteria that are acceptable to the staff for evaluating flaw indications exceeding the 4
allowable flaw size in IW8-3500 are described in IW8-3600 of Section XI of the ASME Code. The six BWNT reports submitted by the licensee on St. Lucie 2 i
pressurizer instrument nozzles were developed based on the above-mentioned i
acceptance criteria of the ASME Code. The staff's evaluation includes the following subjects: transient selection, finite element modelling, film coefficients for the thermal analysis, the proper formula for applied K.
calculations, and the fracture toughness curves (K, lysis,,Ihe crack growth and K ) from Appendix A of Section XI of the ASME Code.
In the fatigue ana rate curves used were from Figure A4300-1 of the same appendix. Water environment curves were used for these surface flaws.
1 3.1 TRANSIENT SELECTION The report reviewed the transients likely to produce maximum tensile stress on the inside surface of the pressurizer. They include 100*F/hr heatup, 200*F/hr cooldown, an upset condition transient of 53*F/hr step-down (pressure - 1740 psia), a 53*F/hr step-up (pressure - 2400 psia), and loss of secondary pressure. A total of 15 cases were analyzed with their stresses documented in Report 32-1235127-02. Among them, the 53 'F/hr step-down transient gavn the highest stresses and was identified as the bounding transient.
In the fatigue analysis, the report assumed 375 cycles of normal heatup/cooldown, 360 cycles of. upset condition transients,150 cycles of leak test, 4 cycles af emergency condition transients, and some secondary normal operating transients. Since all design transients of significance have been considered, the staff agrees with the licensee in its selection of transients and the definition of design transients and their cycles in the fatigue analysis for 30 more years of plant operation.
3.2 FINITE ELEMENT MODELLING To account for the " Hillside Effect" caused by the non-radial penetration of I
the instrument nozzle to the pressurizer wall, the report used a radius, which is 1.52 times the actual radius of the pressurizer, in its FEM modelling. The i
staff pointed out in the RAI that this approach would take care of the stresses due to the pressure load, but not the stresses due to the thermal load.
In Revision 1 of the reports (the -02 series), the staff's concern is alleviated by the licensee's approach of separating the final nozzle stresses into a pressure part and a thermal part and increasing the thermal part by 20%
to account for the Hillside Effect. An assessment of the effect of model radius on thermal stresses was given in (2).
It should be pointed out that a mistake in the equation for calculating the non-radial nozzle stress concentration factor, K, in the previous version of the reports (the -00 and -01 series) has been corrected in Revision 1 of the reports. 'As a result, the multiplying factor applied to the radius of the FEM modelling was reduced from 2.5 to 1.52 and the overall safety margins for 1
crack growth increased significantly.
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3.3 FILM COEFFICIENTS In the thennal analysis, the report used heat transfer coefficients in the water space instead of the coefficients in the steam space. This resulted in conservative tensile stresses because of the use of lower heat transfer coefficient in heating and higher coefficient in cooling of the pressurizer id inf e surface. Specifically, the report used a coefficient of 461 BTU /(hr-ft *F) based on a natural convection in the turbulent region over a i
horizontal plate with an average temperature of 650*F and a delta T of 15'F.
In response to the staff's request to reexamine this coefficient, the licensee expanded its consideration in Revision 1 to include the case for the step-down transient, where p*iling can occur, and used r heat trans/er coefficient of i
10,000 BTU /(hr-ft - F) for that case. The starf considers these values reasonable based on the arguments supplied in [2] and [3]. Further, when i.
ccupared to the heat transfer coefficient used in the inside surface of the pressurizer in a typical RELAP analysis, the report's coefficient appears to be adequate.
3.4 MARGINS BETWEEN APPLIED STRESS INTENSITY FACTOR AND MATERIAL TOUGHNESS In the fracture mechanics analysis, the formula for a nozzle corner crack from an EPRI report [5] was'used to calculate the applied stress intensity factors ksi(in)gusloadcases., the maximum value of the arrest toughness, curve in Appendix for var For the arrest toughness, K, the report used 200 3
Section XI of the ASME Code. Using this upper-shelf value was conservative j
considering the high temperature of the transients in the analysis.
The report employed the boun' ding upset transient of 375 cycles in the fatigue analysis to bound the transients mentioned in Section 3.1, which consist of 375 cycles of normal heatup/cooldown, 360 cycles of upset condition transients,150 cycles of leak test, and 8 cycles of pressure tests. 2The report arrived at an applied stress intensity factor of 46.42 ksi(in) at i
the final flaw size of 0.966 inches for the normal and upset loading condition. The stresses associated with the bounding upset transient were which has a comfo,lable margin over the factor of (10)44 determined by the FEM analysis.
compared to the K
, a safety factor would ensue, r
or 3.16 required by i
the ASME Code. The transient used in the report for the emergency and faulted loading condition is the loss of secondary pressure transient.8The report arrived at an applied stress intensity factor of 84.62 ksi(in) at the final flaw size of 0.966 inches for this transient. A safety factor of 2.36 would beresugedwhenthisappliedstressintensityfactorwascomparedto200 and that of (2),ig,(there is a comfortable margin between the calculated value kst(in)
Aga 1.41) required by the ASME Code.
4.0 CONCLUSION
S The Materials and Chemical Engineering Branch has completed the review and found the submittals acceptable. The staff concludes that the methodology and criteria used in the flaw evaluation for the pressurizer instrument nozzles of St. Lucie 2 plant are in accordance with IW8-3600 of Section XI of the ASME Code. Based on the information provided, the staff also determines that the
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4 fatigue crack growth methodology is adequate. Hence, the ienorted flaws are acceptable '1thout repair for an additional 30 years of plant life. The proposed inservice inspection plan and schedule in Attachment C addresses the i
inservice reexamination requirements of IWB-2420 and is adequate.
5.0 REFERENCES
1.
March 2, 1995, Letter from D. A. Sager of Florida Power & Light Company to USNRC Document Control Desk,
Subject:
St. Lucie Unit 2 Fracture Mechanics Analysis of Pressurizer Instrument Nozzle Flaws.
2.
. July 7, 1995, Letter from D. A. Sager of Florida Power & Light Company to USNRC Document Control Desk,
Subject:
St. Lucie Unit 2 Request for j
Additional Information Fracture Mechanics Evaluation of Pressurizer Instrument Nozzles - Response.
3.
August 2,1995, Letter from D. A. Sager of Florida Power & Light Company to USNRC Document Control Desk,
Subject:
St. Lucie Unit 2 Inservice Inspection Plan, Second Ten Year Interval Revised Stress and Fracture Mechanics Evaluation of Pressurizer Instrument Nozzles - Sunclement.
4.
March 28, 1994, Letter from D. A. Sager of Florida Power & Light Company to USNRC Document Control Desk,
Subject:
St. Lucie Unit 2 Fracture Mechanics Analysis of Pressurizer Instrument Nozzle Flaws.
5.
EPRI Report Number NP-719-SR, " Flaw Evaluation Procedures," with errata for subject report dated April 14, 1980, prepared by ASME Task Group on Flaw Evaluation, Electric Power Research Institute, Palo Alto, California, August 1978.
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SALP INPUT FACILITv NAMES St. Lucie 2 SUMARY OF REVIEW ACTIVITIES On March 2, 1995, Florida Power and Light Company (FPL) submitted, for NRC approval, its fracture mechanics evaluation of st. Lucie 2 pressurizer instrument nozzles. The evaluation is an update of the submittal dated March 28, 1994, which was approved by the NRC on April 1, 1994. The issue was originated from the boric acid leakage frca the "C" instrument nozzle in the pressurizer upper nead, which was detected during the 1994 refueling outage.
The current submittal used IWB-3600 of Section XI of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code and was intended to gain approval without flaw removal or repair for 30-year plant life using i
more realistic assumptions and employing finite element models in the flaw
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evaluation.
j The Materials and Chemical Engineering Branch has completed the review and
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found the submittals acceptable. The staff concludes that the methodology and criteria used in the flaw evaluation for the pressurizer instrument nozzles of St. Lucie 2 plant are in accordance with IWB-3600 of Section XI of the ASME Code. Based on the information provided, the staff also determines that the fatigue crack growth has been dealt with properly. Hence, the reported flaws are acceptable without repair for an additional 30 years of plant life. The licensee's inservice examination plan calls for UT reexamination of the four repaired instrument noz-zles during the next three inspection periods as required by the ASME Code.
NARRATIVE DISCUSSION OF LICENSEE PERFORMANCE-FUNCTIONAL AREA Enaineerina/ Technical Support The licensee, with the help from Babcock and Wilcox Nuclear Technologies, was responsive in providing additional information that led to resolution of several technical issues concerning the finite element modelling and the thermal analysis. The licensee's contractor has sufficient engineering and technical support to adequately address the issue of flaw evaluation.
However, prudent measures should be taken to avoid the kind of mistake incurred in calculating stress concentration factor due to hillside effect.
This mistake alone, which was detected and corrected in Revision 1 of the report, had big effect on the safety margins.
i SAFETY ASSESSMENT /0UALITY VERIFICATigf(
(Not applicable)
Author: Simon Sheng, DE/EMCB 415-2708 ATTACMENT
,,e David B. Matthews are acceptable without repair for an additional 30 years of plant life. The proposed inservice inspection plan and schedule in Attachment C, which addresses the inservice reexamination requirements of IWB-2420 of the ASME Code, calls for ultrasonic reexamination of the four repaired instrument nozzles during the next three inspection periods and is adequate.
This completes our work for Tac No. M91704.
Docket No.: 50-389 Attachments: As stated cc:
Jan Norris, PM DISTRIBUTION:
Central Files EMCB RF/PF JStrosnider BSheron Glainas G:\\SHENG\\5LUCIE2.ISI
- See previous concurrence f
To receive e copy of this document, Indicate in the box C= Copy w/o attachment / enclosure E= Copy with attachment / enclosure N = No copy J
DE:ENCI th E
OFFICE DE:EMCB E
NAME SSheng:ss:adi KMN I
DATE 8/09/95:jb 8/09/95 0FFICIAL COPY
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David B. Matthews are acceptable without repair for an additional 30 years of pla, life.
The proposed inservice inspection plan and schedule in Attachment C, which addresses the inservice reexamination requirements of IWB-2420 of the ASME Code, calls for ultrasonic reexamination of the four repaired instrument nozzles during the next three inspection periods and is adequate.
This comple es our work for Tac No, M91704.
Docket No.: 50-38 \\
Attachments: Asstath N
cc:
Jan Norris, PM g
N, N
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'N l
'NN 1
DISTRIBUTION:
Central Files EMCB RF/PF JStrosnider
)
BSheron Glainas G:\\SHENG\\5LUCIE2.ISI i
To receive a copy of this document, indicate in the box C= Copy w/o attachment / enclosure Es with attachment / enclosure N = No copy
'?
l OFFICE DE:EMCB((
E DE:JMCI/h E
NAME SSheng:ss:[d'l KYba 8/9/95 8k/95 DATE-j
'OfflCIAL COPY