ML20211P841

Safety Evaluation Supporting Alternative Proposed by Licensee to Surface Exam to Perform Boroscopic VT-1 Visual Exam of Pump Casing Welds within Pump Pits for Welds Covered by Relief Request RR-ENG-24

ML20211P841
Person / Time
Site:	South Texas
Issue date:	09/09/1999
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20211P825	List: ML20211P820 ML20211P841
References
NUDOCS 9909140120
Download: ML20211P841 (4)

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j@n uq r Oe d UNITED STATES

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't NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20566-4001 j

4 9 . . . . . ,d SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION OF THE FIRST 10-YEAR INTERVAL INSERVICE INSPECTION PROGRAM PLAN RELIEF REOllEST RR ENG-24 STP NUCLEAR OPERATING COMPANY SOllTH TEXAS PROJECT. UNITS 1 AND 2 DOCKET NOS. 50-498 AND 50-499

1.0 INTRODUCTION

Inservice inspection (ISI) of the American Society of Mechanical Engineers (ASME) Code Class 1,2, and 3 components shall be performed in accordance with Section XI of the ASME l

i 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.  :

l Pursuant to 10 CFR 50.55a(g)(4), ASME Code Class 1,2, and 3 components (including supports) snall meet the requirements, except the design and access provisions and the pre-service 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 corr ponents and system pressure tests conducted during the first 10-year interval and subsequent intervals comply with the requirements in the latest edition and addenda of Section XI of the ASME Code incorporated by reference in 10 CFR 50.55a(b) l 12 months prior to the start of the 120-month interval, subject to the limitations and modifications listed therein. For South Texas Project, Units 1 and 2 (STP), the applicable edition of Section XI of the ASME Code for the first 10-year ISI interval is the 1983 Edition '

through Summer 1983 Addenda.

2.0 DISCUSSON By letter dated February 24,1999, STP Nuclear Operating Company (licensee), submitted relief request RR-ENG-24, seeking relief from the requirements of the ASME Code,Section XI, for STP. The information provided by the licensee in support of the requests for relief from Code requirements has been evaluated and the basis for disposition is documented below.

l 9909140120 990909 PDR ADGCK 05000498 G PDR l

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deauesi,cr Relief RR-ENG 24:

l ASME Code,Section XI, Table IWC-2500-1, Examination Category C-G, item No. C6.10 requires surface examination of 100 percent of the welds of one pump among each group of  ;

muniple pumps of similar design, size, function, and service in e system. Pursuant to 10 CFR '

50.55a(a)(3) the licensee has proposed an alternative to the requirements of ASME Code,Section XI, Table IWC-2500-1, Examination Category C-G, item No. C6.10.

Components for which alternative is reauested: .

Containment spray (CS) pumps 1 A (Unit 1) and 2A (Unit 2): longitudinal seam weld PCW5 and circumferential weld PCW3 Low head safety injection (LHSI) pumps 1 A (Unit 1) and 2A (Unit 2): longitudinal seam weld PCW5 and circumferential weld PCW3 High head safety injection pumps (HHSI) 1 A (Unit 1) and 2A (Unit 2): longitudinal seam l weld PCW5 and circumferential weld PCW3 i

Licensee's Basis for Reauestina Relief (as stated): I The subject outer barrel (pump casing) welds of the affected pumps are located in pump pits. In order to perform a surface examination on the subject casing welds, either the pump would have to be pulled from the associated pit, or the pump motor and pump internals would have to be removed to allow access to the interior of the pump casing. The South Texas Project proposes to use a boroscopic VT-1 visual examination as an alternative to the surface examination.

The South Texas Project believes the boroscopic VT-1 visual examination provides sufficient confirmation that the weld and adjacent base material surfaces are free of significant service-induced degradation and so provides an acceptable level of quality and safety. The accessible welds (or accessible portions of welds)in these pump casings have been examined as required by l Section XI code requirements. No flaws were detected by these examinations.

In addition, a surface examination will be performed on the subject welds if a Containment Spray, Low Head Safety injection, or High Head Safety injection pump is disassembled for maintenance within the inspection interval, allowing access to the subject welds. Consequently, the boroscopic VT-1 visual examination meets the criteria of 10CFR50.55a(a)(3)(i) as an alternate means of examination.

The Containment Spray, Low Head Safety injection, and High Head Safety injection pumps are of a similar centrifugal multiple stage vertical design, and are manufactured by Pacific Pumps. There are five pressure-retaining casing welds associated with each of the subject pump casings: three circumferential casing welds; one suction nozzle weld; and one longitudinal casing weld. Of these welds, only the lower circumferential weld and the lower portion of the longitudinal casing weld are inaccessible for surface examination while a pump is in its pit. The remaining welds have received the required Section XI surface exanhation.

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3 The Containment Spray and Low Head Safety injection pump casings are 24 inches in diameter with approximately a 3-inch annular clearance between the casing and the pit wall. The High Head Safety injection pump casing is 18 inches in diameter with approximately a 6-inch annular clearance. A debris seal covers the annular opening between each pump casing and the edge of the pit.

The lower circumferential weld in each pump casing, located approximately 10 feet down in the pump pit, is inaccessible for surface examination. The 10 feet of each longitudinal casing weld located inside the pump pit are also inaccessible for surface examination. The upper portion of each longitudinal casing weld is 1 accessible for Section XI surface examination for approximately 50 to 55 inches {

of its overalllength. A sketch depicting the typical pump casing and pump pit l configuration is attached.

Licensee's Proposed Alternative Examination (as statedh Due to the small annular space between the pump casing and the pit wall and the distance of the welds from the access opening at the top of the pit (i.e., up to ten feet), performing a complete surface examination of those welds in the installed condition is not practical. However, this configuration is compatible with a boroscopic visual examination of these welds. Boroscopic VT-1 visual examinations were performed December 1 and 2,1998 (Unit 1) and February 3, 1999 (Unit 2) on the entire length of the circumferential and longitudinal pump l casing welds within the pit of each pump subject to inservice inspection. No relevant conditions were identified during these examinations.

In addition to the alternative VT-1 visual examination, a surface examination will be pedormed on the subject welds if a Containment Spray, Low Head Safety injection, or High Head Safety injection pump is disassembled for maintenance within the inspection interval, allowing access to the subject welds. The accessible welds (or accessible portions of welds)in these pump casings have l been examined with a surface examination technique as required by Section XI l code requirements.

3.0 EVALUATION i Alignment of the shaf t along the multiple vertical stages to the driver coupling is critical to proper operation. Improper rigging or alignment can result in a bent pump shaft or vibration and subsequent impaired operation and pump damage. Removal of the pump casing from the pit or removal of the pump internals to gain access to the specified welds to perform a surface examination could have a negative impact if the precise alignment required for these vertical pumps is not achieved when they are returned to service. Therefore, the Code requirements

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are a hardship and unusual difficulty for the licensee without a compensating increase in quality and safety.

The licensee has proposed as an alternative to surface examination to perform a boroscopic  !

VT-1 visual examination of the pump casing welds within the pump pits for the welds covered l by relief request RR-ENG-24. The weld and adjacent base material surfaces will be examined.

The use of a VT-1 boroscopic examination should be able to detect degradation or defects prior to becoming structurally significant. This is because VT-1 examinations are conducted to

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- detect discontinuities and imperfections on the surfaces of components, including such conditions as cracks, wear, corrosion, or erosion. The accessible welds or accessible portions have been examined with a surface examination technique as required by Section XI Code requirements. . No flaws were detected by the licensee's examinations. Additionatif, the licensee proposed that it will perform a surface examination on the specified wew if any of the applicable pumps are disassembled for maintenance within the current inspection interval,

- allowing access to the subject weids. The staff determined that the licensee's proposed alternative provides reasonable assurance of structuralintegrity of the subject welds and that the Code requirements are a hardship and unusual difficulty for the licensee without a compensating increase in quality and safety. Therefore, the licensee's proposed alternative is authorized pursuant to 10 CFR 50.55a(a)(3)(ii) for the current interval.

4.0 CONCLUSION

The staff concludes that the Section XI examination requirements for the subject welds are a hardship and an unusual difficulty on the licensee without a compensa dng increase in the level of quality and safety. Furthermore, the staff concludes that the licensee's proposed alternative and previous inspection results provide reasonable assurance of structuralintegrity of the subject welds. Therefore, the licensee's proposed alternative contained in relief request RR ENG-24 is authorized pursuant to 10 CFR 50.55a(a)(3)(ii).

Principal Contributor: T. McLellan Date: September 9, 1999 i

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