ML20149E074

Safety Evaluation of First ten-year Interval Inservice Insp Program Plan Request to Use ASME Section XI Code Case N-416-1,Houston Lighting & Power Co,South Texas Projects, Units 1 & 2

ML20149E074
Person / Time
Site:	South Texas
Issue date:	07/14/1997
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20149E054	List: ML20149E049 ML20149E074
References
NUDOCS 9707180089
Download: ML20149E074 (6)

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• - n g? k UNITED STATES g j 2

NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20666-0001 l

4 o 9.....g SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATICN OF THE FIRST TEN-YEAR INTERVAL INSERVICE INSPECTION PROGRAM PLAN 1

RE0 VEST TO USE ASME SECTION XI CODE CASE N-416-1 ,

HOUSTON LIGHTING & POWER COMPANY I CITY PUBLIC SERVICE BOARD OF SAN ANTONIO CENTRAL POWER AND LIGHT COMPANY CITY OF AUSTIN. TEXAS SOUTH TEXAS PROJECT. UNITS 1 AND 2 l l

DOCKET NOS. 50-498 AND 50-499 l

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1.0 INTRODUCTION

The Technical Specifications for South Texas Project, Units 1 and 2 (STP)  !

state that the inservice inspection and testing of the American Society of l 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 granted by the Commission pursuant to l 10 CFR 50.55a(g)(6)(i). 10 CFR 50.55a(a)(3) states that alternatives to the requirements of paragraph (g) may be used, when authorized by the NRC, if (1) 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 that become effective

subsequent to editions specified in 10 CFR 50.55a(g)(2) and (g)(3), 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 conductad during the first ten-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) on the date twelve months prior to the start of the 120-month interval, subject to the limitations and modifications listed therein. The applicable edition of Section XI of the ASME Code for the first ten-year inservice inspection interval for the South Texas Project, Units 1 and 2 is the 1983 Edition, 97071800s9 97o714 4 PDR ADOCK 05000498 G PDR

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through Summer 1983 Addenda. The components (including supports) may meet the requirements set forth in subsequent editions and addenda of the ASME Code l incorporated by reference in 10 CFR 50.55a(b) subject to the limitations and modifications listed therein and subject to Commission approval.

Pursuant to 10 CFR 50.55a(g)(5)(iii), if the licensee determines that conformance with an examination requirement of Section XI of the ASME Code is 4 impractical for its facility, information should be submitted to the

. Commission in support of that determination. After evaluation of the ,

determination, pursuant to 10 CFR 50.55a(g)(6)(1), the Commission may grant l relief and may impose alternative requirements that are authorized by law; will not endanger life, property, or the common defense and security; and are otherwise in the public interest, giving due consideration to the burden upon the licensee'that could result if the requirements were imposed.

By letter dated March 26, 1997, Houston Lighting & Power (licensee) requested approval for the implementation of the alternative rules of ASME Section XI Code Case N-416-1 dated February 15, 1994, titled " Alternative Pressure Test Requirement for Welded Repairs or Installation of Replacement Items by Welding, Class 1, 2 and 3,Section XI, Division 1," pursuant to 10 CFR 50.55a(a)(3) to be applied to the inservice inspection (ISI) program for STP.

The NRC staff has reviewed and evaluated the licensee's request and supporting information to use Code Case N-416-1 as a proposed alternative to the Code requirements for STP.

2.0 DISCUSSION CODE CASE N-416-1. " ALTERNATIVE PRESSURE TEST RE0VIREMENT FOR WELDED REPAIRS OR INSTALLATION OF REPLACEMENT ITEMS BY WELDING. CLASS 1. 2 AND 3. SECTION XI.

DIVISION 1" System / Component Aoolicable to Use of Code Case:

ASME Class 1, 2, and 3 Components Code Reauirement Affected by Use of Code Case:

The 1983 Edition through Summer 1983 Addenda, ASME Code,Section XI, IWA-4400(a) requires that a system hydrostatic test be performed following repairs by welding. Similarly, a system hydrostatic test is to be performed following installation of replacement items by welding, as required by ,

IWA-4600. The system hydrostatic tests are to be conducted in accordance with IWA-5000.

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l Licensee's Easis for Reauest: (As stated)-

! " Hydrostatic pressure testing of welded repairs and welded replacements is j required in order to satisfy the referenced Code. However, the South fexas j Project has concluded that such Code hydrostatic testing requirements impose j significant hardships, while adding marginal (if any) value without a ,

j compensating increase in the level of quality and safety. I l

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" Hydrostatic testing performed under the referenced Code subjects the components to a relatively small increase in pressure over the nominal operating pressure and is not intended to present a significant (potentially l destructive) challenge to pressure boundary integrity. Accordingly, 3 hydrostatic pressure testing is primarily regarded as a means to enhance  ;

leakage detection during examination of components under pressure, rather than

i i a measure of the structural integrity of the components. l l

l " Industry experience has demonstrated that leaks are not discovered as a

! result of hydrostatic test pressure propagating a pre-existing flaw through

. the wall of a component. In most cases, leaks are found when the system is at 2 - normal operating pressure. Hydrostatic pressure testing other than that l required by IWA-4000 for repair or replacement is required only upon j installation and at 10-year inspection intervals for Class 1, 2, and

! 3 systems. System leakage tests at normal operating pressure are conducted a l minimum of once each refueling outage for Class I systems and portions of '

l Class 2 systems, and once each 40-month inspection period for Class 3 and the remainder of Class 2 systems. Leaks may also be identified during routine system walkdowns by plant operators and system engineers.

l " Hardships associated with hydrostatic testing performed in accordance with the referenced Code are as follows:

o Hydrostatic pressure testing frequently requires significant effort i in preparation and performance. Since the testing is of questionable benefit, the required resources could be better spent 1- in activities that more effectively assure plant safety and reliability. .

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o Special valve lineups for these tests add unnecessary challenges to 1

maintaining system configuration.

1 o Tests performed inside the radiologically restricted area increase '

the total exposure to plant persennel performing the tasks of modifying and restoring system lineups and removing contaminated test equipment.

"In addition, hydrostatic tests have the added potential to initiate leak paths at mechanical connections (e.g., valve packing gland, flange joints)."

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4 Licensee's Proposed Alternative to Code Reauirement: (As stated) j

" Code Case N-416-1 is proposed as an alternative to IWA-4000 for welded i repairs and installation of replacement items by welding for Class 1, 2 and  ;

3 components. For a system leakage test to be used, Code Case N-416-1 .

requires:

o Performance of NDE in accordance with the methods and acceptance i criteria of the applicable Subsection of the 1992 Edition of  ;

Section III.  ;

o Performance of a . visual examination (VT-2) prior to or immediately upon return to service in conjunction with a system leakage test, l using the 1992 Edition of Section XI, in accordance with IWA-5000, at nominal operating pressure and temperature.

o Documentation of use of this Case on an NIS-2 Form.

, "In addition, the South Texas Project will perform additional surface l examinations on the root pass layer of butt and socket welds on the pressure-retaining boundary of Class 3 components during repair and replacement )

activities. The surface examination method will be in accordance with ASME l Section'III. This additional examination will compensate for the pressure . l' 4 test at normal operating pressure and assure weld quality.

"This proposed alternative to the Code requirement will provide reasonable assurance that flaws will be discovered."

3.0 EVALUATION In lieu of hydrostatic pressure testing for welded repairs or installation of replacement items by welding, Code Case N-416-1 allows a system leakage test using the 1992 Edition of the ASME Code,Section XI, in accordance with paragraph IWA-5000, at r.ominal operating pressure and temperature. This code case also specifies that the non-destructive examination (NDE) of welds be performed in accordance with the applicable Subsection of the 1992 Edition of ASME Code,Section III.

The latest edition of ASME Code,Section XI and Section III, referenced in 10 CFR 50.55a, is the 1989 Edition. The staff has compared the system pressure test requirements of the 1992 Edition of Section XI to those of the

.1989 Edition and determined that the 1992 Edition of the Code imposes a more uniform set of system pressure test requirements for Code Class 1, 2, and 3 systems. The terminology associated with the system pressure test requirements for all three code classes have been clarified and streamlined.

The test frequency and test pressure associated with these tests have not been changed. The hold time for the test has either remained unchanged or increased. The corrective action with respect to removal of bolts from a leaking bolted connection, however, has been relaxed in the 1992 Edition which 1

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5 has been accepted by the staff in previous safety evaluations. Nevertheless, l the NDE requirements of post-weld repair, however, remain the same in both l versions of the Code. Therefore, the staff finds that the requirements of the 1992 ASME Code,Section XI, as referenced in Code Case N-416-1 are equivalent l

to those of the 1989 ASME Code,Section XI.

i Hardships are generally encountered with the performance of hydrostatic j - testing performed in accordance with the Code. For example, since hydrostatic ,

test pressure would be higher than the nominal operating pressure, hydrostatic 1 pressure testing frequently requires significant effort to set up and perform. l

.The need to use special equipment, such as temporary attachment of test pumps and gages, and the need for individual valve lineups can cause the testing to be on critical path.

Piping components are designed for a number of loadings that would be postulated to occur under the various modes of plant operation. Hydrostatic testing only subjects the piping components to a small increase in pressure over the design pressure and, therefore, does not present a significant challenge to pressure boundary integrity. Accordingly, hydrostatic pressure testing is primarily regarded as a means to enhance leakage detection during the examination of components under pressure, rather than solely as a measure to determine the structural integrity of the components.

The industry experience has demonstrated that leaks are not being discovered as a result of hydrostatic test pressures propagating a pre-existing flaw  ;

through walls. The experience, however, indicates that leaks in most cases are being found when the system is at normal operating pressure. This is largely due to the fact that hydrostatic pressure testing is required only upon installation and then once every 10-year inspection interval, while system leakage tests at nominal operating pressures are conducted a minimum of once each refueling outage for Class I systems and each 40-month inspection period for Class 2 and 3 systems. In addition, leaks may be identified by plant operators during system walkdowns which may be conducted as often as once a shift.  !

Following completion of welding, the Code requires volumetric examination of repairs or replacements in Code Class 1 and 2, but requires only a surface examination of the final weld pass in Code Class 3 components. There are no other NDE requirements for Code Class 3 components except for VT-2 visual examination for leaks in conjunction with the 10-year hydrostatic tests and the periodic pressure tests.

Considering the NDE performed on Code Class 1 and 2 systems and considering that the hydrostatic pressure tests rarely result in pressure boundary leaks l that would not occur during system leakage tests, the staff believes that i increased assurance of the integrity ~ of Class 1 and 2 welds is not commensurate with the burden of performing hydrostatic testing. However, considering the nature of NDE requirements for Code Class 3 components, the staff does not believe that elimination of the hydrostatic pressure testing y w  %  %

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l l 6 waile only performing system pressure testing is an acceptable alternative to hydrostatic testing unless additional surface examinations are performed on i the root pass layer of butt and socket welds on the pressure retaining boundary of Class 3 components when the surface examination method is used in accordance with Section III.

For clarification, it should be noted that, consistent with the Code Case l requiring performance of NDE in accordance with the methods and acceptance criteria of the 1992 Edition of Section III, the scope of examination should l

also be in accordance with the 1992 Edition of Section III. The additional surface examination of the root layer of Class 3 pressure retaining welds should be performed only when those pressure retaining welds are required to have a surface examination performed in accordance with the 1992 Edition of Section III. For those Class 3 welds receiving radiography in lieu of a surface examination in accordance with Section III, no additional surface l examination of the root layer needs to be performed.

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4.0 CONCLUSION

The staff concludes that compliance with the Code hydrostatic testing requirements for welded repairs or replacements of Code Class 1, 2 and 3 components would result in hardships without a compensating increase in the level of quality and safety. Accordingly, the licensee's proposed alternative to use Code Case N-416-1 is authorized for STP pursuant to 10 CFR 50.55a(a)(3)(ii) provided that the additional surface examinations are

performed on the root pass layer of butt and socket welds on the pressure retaining boundary of Class 3 components when the surface examination method is used in accordance with Section III, as proposed by the licensee.

l Use of Code Case N-416-1, with the additional surface examination as noted above, is authorized for the duration of the current ten-year ISI interval at STP, until such time as the Code Case is approved by reference in Regulatory Guide 1.147. At that time, if the licensee intends to continue to implement this Code Case, the licensee must follow all provisions in Code Case N-416-1 with limitations issued in Regulatory Guide 1.147, if any.

l Principal Contributor: P. Patnaik Date: July 14,1997 l

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