ML20211F453

Safety Evaluation Supporting Licensee Proposed Alternative to Defer Partial First Period Exams of flange-to-shell Weld to Third Period & Perform Required Ultrasonic Exams,Both Manual & Automated,During Third Period

ML20211F453
Person / Time
Site:	South Texas
Issue date:	08/24/1999
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20211F447	List: ML20211F442 ML20211F453
References
NUDOCS 9908300340
Download: ML20211F453 (4)

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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SECOND 10-YEAR INTERVAL INSERVICE INSPECTION PLAN REQUEST FOR RELIEF RR-ENG-2-13 STP NUCLEAR OPERATING COMPANY SOUTH TEXAS PROJECT. UNITS 1 AND 2 DOCKET NOS. 50-498 AND 50-499 {

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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 Boiler and Pressure Vessel Code and applicable addenda as required by 10 CFR 50.55a(g),

except where specific written relief has been gmnted by the Commission pursuant to 10 CFR 1 50.55a(g)(6)(i). The regulation at 10 CFR 50.55a(a)(3) states that alternatives to the l 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 supports) shall 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 components 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 50.55t(b) 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 second 10-year ISI intervalis the 1989 Edition. l 2.0 DISCUSSION By letter dated May 13,1999, S TP Nuclear Operating Company (licensee), submitted Request for Relief RR-ENG-2-13, seeking relief from the requirements of the ASME Code,Section XI, for STP, Units 1 and 2. The information provided by the licensee in support of the requests for i relief frorr Code requirements has been evaluated and the basis for disposition is documented I

below.

' 9908300340 990U24 PDR ADOCK 05000498 o PDR

2.1 Reauest for Relief No. RR-ENG-2-13 Section XI Examination Category B-A, Item No. B1.30 (flange-to-shell weld) allows ultrasonic examinations conducted on this weld from the vessel shell to be deferred to the third period if a partial examination of this weld is conducted from the vessel flange seal surface during the first period. This partial examination in the first period is typically a manual ultcasonic examination conducted from the flange seal surface of 50 percent of the length of the flange-to-shell weld. ]

The remaining 50 percent of this weld is examined manually from the flange seal surface in the i third period, usually in conjunction with the automated reactor pressure vessel examinations.  !

The entire weld length is also examined in the third period from the vessel shell with automated ultrasonic equipment.

3 Pursuant to 10 CFR 50.55a(a)(3)(ii), the licensee proposes as an alternative to defer the partial first period examinations of the flange-to-shell weld to the third period.

2.2 Licensee's Basis for Reauestina Relief (as stated)  ;

The South Texas Project requests relief from the examination scheduling requirements of the referenced code for reactor pressure vessel flange-to-shell welds in accordance j with 10 CFR 50.55a(a)(3)(ii). The South Texas Project believes that complying with the code schedule requirements will result in a hardship or unusual difficulty without a compensating increase in the level of quality and safety. 3 1

Performing partial manual ultrasonic examinations from the flange seal surface in both the first and third periods increases the overall level of radiation exposure to examination and support personnel as compared to a complete examination of this weld in the third period. Ultrasonic examination of this weld is performed during the initial vessel head lift at the beginning of a refueling outage. Support craft and non-destructive examination personnel have to climb down from the operating deck to the drained refueling cavity to reach the vessel flange. Support craft remove the vessel 0-rings from the flar:ge seal surface and secure them on brackets to allow scanning from the j flange seal surface. The time required to remove the O-rings and scan half this weld is nearly identical to that required to scan the entire weld. Therefore, scanning half this l t

weld in two different periods nearly doubles the radiation dose to plant personnel. j The South Texas Project believes performing partial examinations of the flange-to-shell welds from the flange seal surface in the first and third periods is not necessary to ,

assure the structural integrity of these welds. The requirement for a partial examination i of certain reactor vessel welds during the first inspection period was established in the early editions of Section XI. Because there was very limited operating experience with reactor pressure vessels, these partial examinations provided additional assurance that no flaws were developing. Because most reactor vessel welds can practically be .

examined only at ten-year intervals, the code selected some accessible welds (e.g.,

flange-to-shell, outlet noule-to-shell and inner radius) for partial examination within l each interval. Now that the industry has accumulated hundreds of years of reactor operating experience with no service-induced failures of the vessel shell welds, these i partial weld examinations are no longer justified. The partial examinations of the reactor vessel nonles have already been eliminated by Code Case N-521 as discussed below.

3-The South Texas Project recently completed the ten-year inservice inspections of the Unit 1 reactor pressure vessel. The results of these vesselinspections, including the examination of the flange-to-shell weld, were acceptable, and consistent with hictorical industry experience. -

Section XI Code Case N-521, approved by the Nuclear Regulatory Commission, provides for an alternative, ten-year examination period for other reactor pressure vessel welds (i.e., nozzle-to-shell weld, nozzle inner radius, and nozzle-to-safe end weld) that are subject to higher operational loadings, and higher levels of neutron fluence than the flange-to-shell weld. The South Texas Project believes the examination frequency for flange-to-shell welds should be no higher than once per ten years as required for the reactor pressure vessel welds addressed in Code Case N-521.

Based upon the above, the South Texas Project believes the requested deferral of the partial flange-to-shell weld is justified based on ALARA [ as low as reasonably achievable] considerations, impact on quality and safety, operational experience, and the precedent set by Code Case N-521.

2.3 Licensee's Proposed Alternative Examination (as stated)

In lieu of performing a manual ultrasonic examination of 50% of the length of the reactor pressure vessel flange-to-shell weld from the flange seal surface in the first period, the South Texas Project will perform the required ultrasonic examinations, both manual and automated, during the third period.

3.0 EVALUATION The licensee proposes, as an alternative, to defer the partial first period examinations of the flange to-shell weld to the third period and it will perform all the required ultrasonic examinations, both manual and automated, during the third period.

Performing partial manual ultrascnic examinations from the flange seal surface in both the first and third periods increases the overall level of radiation exposure to examination and support personnel as compared to a complete examination of this weld in the third period. Ultrasonic examination of this weld is performed during the initial, vessel head lift at the beginning of a refueling outage. Support craft and non-destructive examination personnel are required to climb down from the operating deck to the drained refueling cavity to reach the vessel flange.

Support craft remove the vessel O-rings from the flange seal surface and secure them on brackets to allow scanning from the flange seal surface. The time required to remove the O-rings, set up the non-destructive examination test equipment, and scan half this weld is nearly identical to that required to scan the entire weld. Therefore, scanning half this weld in two different periods nearly doubles the radiation dose to plant personnel.

l Performing partial examinations of the flange-to-shell welds from the flange seal surface in the first and third periods is not necessary to assure the structuralintegrity of these welds. The requirement for a partial examination of certain reactor vessel welds during the first inspection period was established in the early editions of Section XI. At the time of early Code editions, there was limited operating experience with reactor pressure vessels and the partial examinations provided additional assurance that no flaws were developing. The industry has

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.4 accumulated hundreds of years of reactor operating experience with no service-induced failures cf the vessel shell welds. In addition, STP recently completed its 10-year Isis of the Unit 1

> reactor pressure vessel. The results of these vesselinspections, including the examination of the flange-to-shell weld, were a:ceptable, and consistent with historicalindustry experience.

4.0 CONCLUSION

. On the basis of its review, the staff concludes that compliance with the Code requirement to do a partial examination of the subject weld from the vessel flange seal surface during the first period constitutes a hardship without a compensating increase in the level of quality and safety.

The licensee's proposed alternative to defer the partial first period examinations of the flange-to-shell weld to the third period and to perform all the required ultrasonic examinations, both manual and automated, during the third period provides reasonable assurance of structuralintegrity of subject component. Accordingly, the licensee's proposed alternative is authorized pursuant to 10 CFR 50.55a(a)(3)(ii) for the second ISI interval.

Principal Contributor: T. McLellan Date: August 24, 1999 l l

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