ML20217K915

SER Authorizing Util Relief Request RR-ENG-2-3 for Second 10-year ISI Interval of Stp,Units 1 & 2 Pursuant to 10CFR50.55a(a)(3)(i)

ML20217K915
Person / Time
Site:	South Texas
Issue date:	10/15/1999
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20217K913	List: ML20217K909 ML20217K915
References
NUDOCS 9910270028
Download: ML20217K915 (3)

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, g ,j NUCLEAR REGULATORY COMMISSION o 'f WASHINGTON, D.C. 20555 4001

• • • • • ,o SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO THE SECOND 10-YEAR INSERVICE INSPECTION PROGRAM RELIEF REQUEST PR-ENG-2-3 STP NUCLEAR OPERATING COMPANY SOUTH TEXAS PROJECT. UNITS 1 AND 2 DOCKET NOS. 50-498 AND 50-499

1.0 INTRODUCTION

By letter dated June 9,1999, STP Nuclear Operating Company (the licensee) submitted a request for relief from the American Society of Mechanical Engineers (ASME) Code,Section XI, nondestructive examination requirements applicable to South Texas Project (STP), Units 1 and 2, pressurizer suppo'rt attachment welds (Relief No. RR ENG 2 3). The licensee proposes to perform an alternative ultrasonic examination from the outside surface of the skirt attachment weld,in lieu of a surface examination on the inside of the pressurizer skirt. The licensee's relief request is applicable to the second 10-year inservice inspection (ISI) interval for STP, Units 1 and 2.

2.0 BACKGROUND

f ISI of the ASME Code Class 1,2, and 3 components shall be performed in accordance with l Section XI of the ASME Boiler and Pressure Vessel (B&PV) Code and applicable addenda as required by 10 CFR 50.55a(g), except where specific written relief has been granted by the Commission pursuant to 10 CFR 50.55a(6)(g)(i), The regulation at 10 CFR 50.55a(a)(3) states that alternatives to the requirements of paragraph (g) may be used, when authorized by the NRC, if (i) the proposed alternatives would provide an acceptable level of quality and safety or (ii) compliance with the specified requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.

Pursuant to 10 CFR 50.55a(g)(4), ASME Code Class 1,2, and 3 components (including i supports) shall meet the requirements, except the design and access provisions and the preservice examination requirements, set forth in the ASME Code,Section XI, " Rules for Inservice Inspection of Nuclear Power Plant Components," to the extent practical within the limitations of design, geometry, and materials of construction of the components. The regulations require that inservice examination of components and system pressure tests conducted during the first 10-year interval and subsequent intervals comply with the l requirements in the latest edition and addenda of Section XI of the ASME Code incorporated by reference in 10 CFR 50.55a(b) 12 months prior to the start of the 120-month interval, subject to Enclosure 9910270028 991015 PDR ADOCK 05000498 P PDR

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- the' limitations and modifications listed therein. For STP, Units 1 and 2, the apolicable edition of

.Section XI of the ASME Code for the second 10-year ISI intervalis the 1989 Edition.

3.0 - LICENSEE'S REQUEST  !

r The comoonents for which relief is reauested

Pressurizer support skirt attachment welds for Unit 1 (pressurizer 1 A, weld number  !

1R111NPZ101 A) and Unit 2 (pressurizer 2A, weld number 2R112NPZ201 A) l I

. Anolicable Code reouirement from which relief is reauested ASME Code,Section XI, Table IWB-2500-1, Examination Category B-H, and Figures IWB-2500-13,-14,'and 15 require surface (i.e., magnetic particle) examination of the interior l

surfaces of the support skirt attachment weld and adjacent base materiallocated inside the l pressurizer support skirt. j l

Licensee's Basis for Reauestina Relief (as stated) in accordance'with the provisions of 10CFR 50.55a(a)(3)(i), the South Texas Project requests relief from the ASME Section XI requirement for a surface examination of the inside surface of the Unit 1 and Unit 2 pressurizer support skirt attachment weld. .This relief request proposes application of an ultrasonic examination as an alternative approach to surface examination of the subject weld.

ASME Section XI requires that integral attach &nts to Class 1 vessels be examined by either a surface or volumetric examination method, depending on the specific design of the attachment. The configuration of the skirt attachment

' welds most nearly resembles that of Figure IWB-2500-13 of Section XI (Figure 1). This figure requires surface examination of both the exterior (A B) and interior (C-D) surfaces of the attachment weld and adjacent base materials.

However, the configuration of the South Texas Project pressurizers (see UFSAR (updated final safety analysis report) Figures 5.4-10 and -15) does not permit adequate access to the interior examination area to perform the specified

. magnetic particle examination. Pressurizer heaters, located approximately 13

-inches from the inside surface of the support skirt, restrict access to this area.

. Licensee's Proposed Altemative Examination (as stated)

In lieu of the magnetic particle examination of the inside surface of the skirt attachment weld, the South Texas Project proposes to perform an ultrasonic

. examination from the outside surfaces of the attachment weld and adjacent base materials. The extent of the ultrasonic examination coverage is shown on the attar;hed sketch (Figure 2). This ultrasonic examination will provide coverage of theinterior surfaces that would have been examined by the internal magnetic particle examination. Furthermore, this ultrasonic examination will provide coverage of the attachment weld and portions of adjacent base material volumes not obtainable by magnetic particle examination. A magnetic particle g

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examination will be conducted on the exterior surfaces of the attachment weld and adjacent base materials (examination surface A-B)in accordance with Section XI.

Licensee's Justification for Grantino Relief (as stated)

The South Texas Project requests relief from the requirement for magnetic particle examination of the inside surface of the pressurizer support attachment weld and proposes an alternative ultrasonic examination as described above in accordance with 10 CFR 50.55a(a)(3)(i). The proposed ultrasonic examination is expected to provide results at least comparable to those from a magnetic particle surface examination, as well as cover a wider area. Consequently, the South Texas Project believes the proposed alternative ultrasonic examination will provide an acceptable level of quality and safety.

4.0 EVALUATION The applicable code requirements for the licensee's second 10-year ISI interval would require the licensee to perform a magnetic particle examination on the interior and exterior surfaces of the support skirt attachment welds (ASME Code,Section XI,1989 Edition, Table IWB 2500, Examination Category B-H). Performing the required surface examination on the interior surface of the support skirt attachment welds is not feasible due to inadequate access to the interior examination area of the support skirt attachment welds. The licensee proposes to perform an ultrasonic examination from the exterior surface of the support skirt attachment welds.

The code-required magnetic particle examination is intended to provide detection of surface crack initiation, but does not provide information on the depth of the cracks. The proposed ultrasonic examination would be expected to reveal cracking before it becomes significant and provides an estimate of crack depth. The ultrasonic examination can be performed on the exterior surface of the weld and provides indication of discontinuities throughout the volume of the material. Therefore, the' staff finds the licensee's proposed alternative of performing an ultrasonic examination on the exterior surface of the support skirt attachment welds will provide acceptable assurance of structuralintogrity by identifying any significant indications in the support skirt attachment welds.

5.0 CONCLUSION

Based on the above evaluation, the staff has determined that the code-required examination is not feasible to perform on the interior surface of the support skirt attachment welds. The staff concludes that the licensee's proposed alternative to perform an ultrasonic examination to detect flaws in the weld provides an acceptable level of quality and safety. Therefore, pursuant to 10 CFR 50.55a(a)(3)(i), the alternative proposed in relief request RR ENG-2 3 is authorized for the second 10 year ISI interval of the STP, Units 1 and 2.

Principal Contributor: A. Keim Date: October 15, 1999