ML20136D783
| ML20136D783 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 03/10/1997 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20136D780 | List: |
| References | |
| NUDOCS 9703130011 | |
| Download: ML20136D783 (5) | |
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UNITED STATES
, , I, NUCLEAR REGULATORY COMMISSION 2 WASHINGTON, D.C. *amas -3
. . . . . ,o SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION OF REQUEST FOR RELIEF TENNESSEE VALLEY AUTHORITY BROWNS FERRY NUCLEAR PLANT UNIT 3 j DOCKET NO. 50-296 l.0 INTRODUCTION 4
! The Technical Specifications for Browns Ferry Nuclear Plant (BFN) Unit 3
+ states that the inservice inspection and testing 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 granted by the Commission pursuant to i 10 CFR 50.55a(g)(6)(1). 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 un) usual difficulty without a compensating increase in the lei 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 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 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 12 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 BFN Unit 3 second 10-year inservice inspection (ISI) interval is the 1989 Edition (no addenda). The components (including supports) may meet the requirements set forth in subsequent editions and addenda of the ASME Code incorporated by reference in 10 CFR 50.55a(b),
subject to the limitations and modifications listed therein and subject to Commission approval.
l By letter dated January 22, 1997, the Tennessee Valley Authority (the licensee) submitted the ASME Section XI inservice inspection and system pressure test programs for the second inspection interval for BFN Unit 3. As ENCLOSURE 9703130011 970310 6 DR ADOCK 0500
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I part of this submittal, the licensee requested approval for the implementation of the alternative rules of ASME Section XI Code Case N-416-1 dated February 15, 1994, entitled " 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 BFN Unit 3. The licensee provided additional information on February 13, 1997, correcting a reference in the original submittal. The NRC staff evaluation of this request is given below.
i Other relief requests which are part of the licensee's submittal are being evaluated separately.
1 2.0 EVALUATION l 2.1 Licensee's Request I As an alternative to the exhting Section XI requirements, BFN will utilize the provisions of ASME Code Case N-416-1 along with the following additional l NDE [non-destructive examination) requirements for Class 3 components.
When performing repairs by welding or the installation of replacement items by welding on the pressure retaining boundary of Class 3 components, NDE shall be performed in accordance with the methods and acceptance criteria of Subsection ND of the 1992 Edition of Section III. In addition, when the surface examination method is used in accordance with ND-5222 [ corrected reference
, provided in the licensee's letter of February 13,1997] for a butt or socket i weld, an additional surface examination shall be performed on the root (pass)
! layer.
, 2.2 Licensee's Component Identification
! ASME Class 1, 2, and 3 Piping Systems 1
- 2.3 ASME Code Section XI Requirements J
The ASME Boiler and Pressure Vessel Code,Section XI, 1989 Code Edition IWA-4400(a) and IWA-4600(a) require the performance of hydrostatic testing on 4
pressure retaining boundaries of Class 1, 2, and 3 components after repairs by welding or the installation of replacement items by welding.
2.4 Proposed Alternative Examination The licensee proposes to apply Code Case N-416-1 for welded repairs or installation of replacement items by welding in Class 1, 2, and 3 piping, with additional NDE as discussed in Section 2.1.
2.5 Licensee's Basis for Request 1
The licensee's January 22, 1997 letter provided the following basis for use of l Code Case N-416-1: l Elevated pressure tests are difficult to perform and often represent a true hardship. Some difficulties associated with elevated pressure testing include the following:
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- Hydrostatic testing often requires complicated or abnormal valve line-ups in order to properly vent, fill, and
- isolate the components requiring testing.
- Relief valves with setpoints lower than the hydrostatic j
test pressure must be gagged or removed and blind flanged.
This process requires the draining and refilling of the i
system.
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- Valves that are not normally used for isolation (e.g.,
normally open pump discharge valves) are often required to 5
! provide pressure isolation for an elevated pressure hydrostatic test. These valves frequently require time 4
consuming seal maintenance in order to allow for
! pressurization.
- The radiation exposure required to perform a hydrostatic pressure test is high in comparison to a system leakage j -test. The amount of time required to prepare the volume i
' for hydrostatic pressure testing (i.e., installing relief valve gags, performing appropriate valve line-ups, etc.)
- is significantly large.
1 l' - Temporary support installation and pinning of spring cans j are sometimes needed to compensate for the additional
! weight added to systems during hydrostatic tests.
The difficulties encountered in performing a hydrostatic pressure test are prohibitive when weighed against the benefits. Industry ,
l experience, which is supported by BFN's experience, shows that most through-wall leakage is detected during system operation as j opposed to elevated pressure tests.
I Little benefit is gained from the added challenge to the piping 1
' system provided by an elevated pressure hydrostatic test (when compared to a system leakage test), especially when one considers that the piping stress experienced during a hydrostatic test does not include the stresses associated with the thermal growth and l dynamic loading for design basis events.
I The acceptability of performing nominal operating pressure tests, j in lieu of hydrostatic tests, is supported by the approval by the l Board of Nuclear Codes and Standards of ASME Code Case N-416-1, l
! " Alternative Pressure Test Requirements for Welded Repairs or l i
Installation of Replacement Items by Welding." This code case allows a system leakage test at nominal operating pressure and i temperature to be used in lieu of a hydrostatic test, provided
- - that non-destructive examination (NDE) of the weld (s) is performed i in accordance with the methods and acceptance criteria of the
- applicable Subsection of the 1992 Edition of Section III.
j TVA [the licensee] considers that the above guidance is sufficient
- for Code Class 1 and 2 components since the code requires q volumetric examination of repairs or replacements in Code Class 1 t
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i and 2 components. However, the code only requires a surface examination of the final weld pass in Code Class 3 components.
, Accordingly, TVA proposes to supplement the examination requirements specified in N-416-1 with additional aurface examinations as specified below (See Sections 2.1 and 2.4] in the .
] Alternative Testing description. ,
! 2.6 Staff Evaluation i In lieu of hydrostatic pressure testing for welded repairs or instaliation of
! replacement items by welding, Code Case N-416-1 requires a visual examination i
! (VT-2) be performed in conjunction with a system leakage testing using the ;
, 1992 Edition of Section XI, in accordance with paragraph IWA-5000, at nominal i operating >ressure and temperature. This code case also specifies that NDE of -
i the welds >e performed in accordance with the applicable Subsection of the 1992 Edition of Section III.
The 1989 Edition of Sections XI and III are the latest editions referenced in 10 CFR 50.55a. The staff has compared the system pressure test requirements of the 1992 Edition of Section XI to the requirements of IWA-5000 of the 1989 Edition of Section XI. In summary, the 1992 Edition 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 has been clarified and streamlined. The test frequency and test pressure conditions associated with these tests have not been changed.
The hold times for these tests have either remained unchanged or increased.
The post-welded repair NDE requirements of the 1992 Edition of Section III remain the same as the requirements of the 1989 Edition of Section III. l Therefore, the staff finds this aspect of Code Case N-416-1 to be acceptable. l Hardships are generally encountered with the performance of hydrostatic l testing performed in accordance with the Code. For example, since hydrostatic l test pressure would be higher than nominal operating pressure, hydrostatic l 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 gauges, 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 indicates that experience has demonstrated that leaks are not being discovered as a result of hydrostatic test pressures propagating a preexisting flaw through wall. They indicate that, when leaks are found, in most cases they are 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
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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 routine system walkdowns.
1 Following the performance of welding, the code requires volumetric examination !
of repairs-or replacements in Code Class I and 2, but only requires a surface !
exannation of the final weld pass in Code Class 3 piping components. There !
are no ongoing NDE requirements for Code Class 3 components except for visual l exnnination 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 n rely result in pressure boundary leaks 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 eliminating the hydrostatic pressure testing and ;
only performing system pressure testing is an acceptable alternative to i hydrostatic testing unless 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. The licensee's proposed alternate testing includes this additional surface examination.
- With the licensee's commitment to perform additional surface examinations on the root pass layer of butt and socket welds as discussed above, 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 BFN Units 1, 2, and 3, pursuant to 10 CFR 50.55a(a)(3)(ii), provided 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.
Use of Code Case N-416-1 is authorized until such time as the Code Case is published in a future revision of Regulatory Guide 1.147. At that time, if the licensee intends to continue to implement this code case, the licensee is to follow all provisions in Code Case N-416-1, with limitations issued in Regulatory Guide 1.147, if any.
Principal Contributor: J. Williams Dated: March 10, 1997