ML17291A799
| ML17291A799 | |
| Person / Time | |
|---|---|
| Site: | Columbia  |
| Issue date: | 05/12/1995 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML17291A797 | List: |
| References | |
| NUDOCS 9505180234 | |
| Download: ML17291A799 (6) | |
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UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 2055&0001 S
FETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION INSERVICE INSPECTION RE VEST FOR RELIEF AS ING ON PUB IC 0
SUP LY S S
NUCLEAR PROJECT NO.
2 DOCKET NO. 50-397
- 1. 0 INTRODUCTION The Technical Specifications for Washington Nuclear Project No.
2 (WNP-2) state that the inservice inspection and testing of the American Society of Mechanical Engineers (ASHE) Code Class 1, 2, and 3 components shall be performed in accordance with Section XI of the ASHE 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 10 CFR 50.55a(g)(6)(i).
Section 50.55a(a)(3) of Title 10 of the Code of Federal Regulations 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 difficulties without a compensating increase in the level of quality and safety.
Pursuant to 10 CFR 50.55a(g)(4),
ASHE 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 ASHE 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 ASHE 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 ASHE Code for the WNP-2 second 10-year inservice inspection (ISI) interval is the 1989 Edition.
The components (including supports) may meet the requirements set forth in subsequent editions and addenda of the ASHE Code incorporated by reference in 10 CFR 50.55a(b) subject to the limitations and modifications listed therein and subject to Commission approval.
9505180234 950512 PDR ADQCK 05000397 P
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Pursuant to 10 CFR,50.55a(g)(5)(iii), if the licensee determines the conformance with an examination requirement of Section XI of the ASHE Code is impractical for its facility, information shall be submitted to the Commission in support of that determination.
After evaluation of the determination, pursuant to 10 CFR 50.55a(g)(6)(i),
the Commission may grant relief and may impose alternative requirements that are determined to be 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 December 27, 1994, the Mashington Public Power Supply System (the licensee) requested approval for the implementation of the alternative rules of ASHE 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 Melding 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 WNP-2.
- 2. 0 EVALUATION Code Case N-416-1 Alternative Pressure Test Re irement for Welded Re airs or Installation of Re lacement Items b
Weldin Class 1
2 and 3 - Section XI Division 1
Com onent Identification ASHE Class 1, 2, and 3 piping systems ASHE Code Section XI Second Interval Re uirements The 1989 Edition,Section XI, IWA-4700(a) requires that a system hydrostatic test be performed in accordance with IMA-5000 after repairs by welding on the pressure retaining boundary.
Licensee's Basis for Re uest "There will be no adverse impact on plant quality and safety by implementing Code Case N-416-1 requirements on ASHE Section III Code Class 1, 2, and 3 welded joints due to the use of NDE j nondestructive examination]
examination and NDE examination acceptance criteria of ASHE Section III, 1992 Edition and the alternate pressure test requirements at nominal operating pressure.
The ASHE Section III related piping systems and components at WNP-2 were constructed (material, designed, fabricated, installed, examined and tested) in accordanc
. with ASHE Section III requirements.
The welded repairs or installation of replacement by welding will be performed in accordance with ASME Section XI, 1989 Edition and ASME Section III, (Code Edition and Addenda applicable to the component) requirements except that the NDE and pressure test requirements will be in accordance with Code Case N-416-1.
The final welds for welded joints in ASME Section III, Code Class 1
(NB) and 2
(NC) piping systems and components will be NDE examined in accordance with ASHE Section III, NX-5000, 1992 Edition requirements.
The NDE examination acceptance criteria for Code Class 1 and 2 will also be in accordance with ASHE Section III, NX-5000, 1992 Edition requirements as required by Code Case N-416-1.
The final welds for welded joints over 2" nominal pipe size (NPS) in ASHE Section III, Code Class 3 piping systems and components will be NDE examined by either magnetic particle (MT) or liquid penetrant (PT) examination as required by ASHE Section III, ND-5000,'992 Edition.
The NDE examination acceptance criteria will also be in accordance with ASHE Section III, ND-
- 5000, 1992 Edition requirements as required by Code Case N-416-1.
The final welds for welded joints less than 2" nominal pipe size (NPS) in ASHE Section III, Code Case 3 piping systems and components will be NDE examined by either magnetic particle (HT) or liquid penetrant (PT) examination in lieu of visual examination as required by ASHE Section III, ND-5000, 1992 Edition.
The VT-" 2 visual examination will be performed in conjunction with a system leakage test in accordance with ASHE Section XI, IWA-
- 5000, 1992 Edition requirements as required by Code Case N-416-1.
The purpose of the hydrostatic test on the welded joints is to verify the leak tightness of the joint.
The ability to identify a potential leak in the welded joint would be the same during a
system leakage test at nominal operating pressure per Code Case N-416-1 as it would be at elevated pressure test of 1. 1 X design pressure through 1.25 X design pressure for the hydrostatic test of ASME Section XI.
Pro This relief request for use of Code Case N-416-1 requirements will be implemented during the second 10-year interval whenever a
hydrostatic test is required subsequent to welded repairs or installation of replacements by welding is performed in accordance with ASME Section XI and ASME Section III requirements."
osed Alternative Examination The licensee proposes to apply Code Case N-416-1 as an alternative for welded repairs or installation of replacement items by welding in Class 1, 2, and 3
piping.
In addition, the licensee proposes to perform either magnetic particle or liquid penetrant examinations on welded joints less than 2"
nominal pipe size in Code Class 3 piping and components.
valuat'o In lieu of hydrostatic pressure testing for welded repairs or installation of replacement items by welding, Code Case N-416-1 requires a visual examination (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 operating pressure and temperature.
This code case also specifies that NDE of the welds be 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 corrective actions with respect to removal of bolts from leaking bolted connections have been relaxed in the 1992 Edition.
This relaxation has been accepted by the staff in previous safety evaluations.
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. Therefore, the staff finds this aspect of Code Case N-416-1 to be acceptable.
Hardships are generally encountered with the performance of hydrostatic testing performed in accordance with the Code.
For example, since hydrostatic test pressure would be higher than nominal operating pressure, hydrostatic pressure testing frequently requires significant effort to set up and perform.
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 preexisting flaw through wall.
This experience 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 1 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 the performance 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 piping components'here are no ongoing NDE requirements for Code Class 3 components except for visual examination for leaks in conjunction with the 10-year hydrostatic tests and the periodic pressure tests'onsidering the NDE performed on Code Class 1 and 2 systems and considering that the hydrostatic pressure tests rarely result in pressure boundary leaks that would not occur during system leakage tests, the staff believes that 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 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 For clarification, it should be noted that, consistent with the Code Case requiring performance of NDE in accordance with the methods and acceptance criteria of the 1992 Edition of Section III, the scope of examination should also be in accordance with the 1992 Edition of Section III'he 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 examination of the root layer needs to be performed 3 ~ 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 WNP-2, pursuant to 10 CFR 50.55a(a)(3)(ii) provided 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.
Use of Code Case N-416-1, with the proposed additional surface examination as noted above, is authorized through the duration of the second ten-year Inservice Inspection Program Plan Principal Contributor:
H. A. Hiller Date:
Hay i2, f995