ML18064A704
| ML18064A704 | |
| Person / Time | |
|---|---|
| Site: | Palisades  |
| Issue date: | 04/13/1995 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML18064A703 | List: |
| References | |
| NUDOCS 9504190236 | |
| Download: ML18064A704 (7) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION INSERVICE INSPECTION REQUESTS FOR RELIEF FOR CONSUMERS POWER COMPANY PALISADES PLANT DOCKET NO. 50-255
- 1. 0 INTRODUCTION The Technical Specifications for Palisades Plant state that the inservice inspection (ISI) and testing of the American Society of Mechanical Engineers (ASME) Code Class l, 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 IO CFR 50.55a(g), except where specific written relief has been granted by the Commission pursuant to 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 (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), ASME Code Class l, 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 IO-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 I20-month interval, subject to the limitations and modifications listed therein.
The 1983 Edition, Summer 1983 Addenda, of Section XI is the applicable edition of the ASME Code for the Palisades Plant, second 10-year ISI interval.
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.
In a letter dated March 3, 1995, the licensee, Consumers Power Company (CPC),
proposed an alternative examination to the requirements of the ASME Boiler and Press~re Code,Section XI.
CPC requested approval for the implementation of the alternative rules of ASME Section XI Code Case N-416-1, dated February 15, 1994, "Pressure Test Requirements for Welded Repairs or Installation of
e e Replacement Items by Welding, Class 1, 2, and 3 Section XI, Division l,"
pursuant to 10 CFR 50.55a(a)(3) to be applied to ISI for the Palisades Plant.
- 2. 0 EVALUATION 2.1 Licensee's Request The licensee's March 3, 1995, letter stated the following request:
The ASME Code Case N-416, "Alternative Rules for Hydrostatic Testing of Repair or Replacement of Class 2 Piping" allowed for hydrostatic testing at nominal system operating pressure of Class 2 piping following welded repair or replacement activities.
Code Case N-416 has been endorsed for use by the NRC under Regulatory Guide 1.147, "Inservice Inspection Code Case Acceptability, ASME Section XI Division I.
11 Code Case N-416-1, "Alternative Pressure Test Requirement for Welded Repairs or Installation of Replacement Items by Welding, Class l, 2 and 3 Sec;tion XI, Division I" expands the scope of the N-416 alternate rules for Class 2 piping to Class l, 2 and 3 systems.
Due to its recent approval, Code Case N-416-1 has not yet been endorsed by the NRC in Regulatory Guide 1.147.
It is our understanding, however, that NRC approval has been granted for other licensees to use this Code Case.
Therefore, in accordance with footnote 6 to 10 CFR 50.55a, we request approval for use of Code Case N-416-1 for plant testing beginning with the 1995 refueling outage, which is scheduled to start in late May of this year.
2.1.1 Licensee's Component Identification Components identified for this relief include Class l, 2, and 3 systems subject to hydrostatic testing.
2.1.2 ASME Code,Section XI, Second Interval Requirements The 1983 Edition through Summer 1983 Addenda,Section XI, IWA-4400(a) requires that a system hydrostatic test be performed in accordance with IWA-5000 after repairs by welding on the pressure-retaining boundary.
2.1.3 Licensee's Proposed Alternative Examination The licensee proposes to apply Code Case N-416-1 as alternative rules for welded repairs or installation of replacement items by welding in Class 1, 2, and 3 piping.
CPC proposes the following alternatives in conjunction with use of Code Case N-416-1:
After welded repairs or installation of replacement items by welding, the following alternative requirements will be met in lieu of performing the hydrostatic pressure test required per paragraph IWA-4000:
(a) NDE shall be performed in accordance with the methods and acceptance criteria of the applicable Subsection of the 1992 Edition of Section III.
(b) Prior to or immediately upon return to service, a visual examination (VT-2) shall be performed in conjunction with a system leakage test, using the 1992 Edition of Section XI, in accordance with paragraph IWA-5000, at nominal operating pressure and temperature.
(c) Use of this Relief Request shall be documented on an NIS-2 Form.
(d) When NOE is to be conducted per Subsection N0-5222 on a Code Class 3 component, an additional surface examination shall be performed on the root {pass) layer.
{e} When Code Class 3 repair or replacement activities involve socket/fillet welds, a surface examination shall be performed on the subject socket/fillet welds.
The NOE requirements a, b and c are required when implementing Code Case N-416-1 as specified in the code case.
It is our understanding that the additional NOE requirements specified in d and e above will apply to Class 3 repair or replacement activities when the code case is endorsed by the NRC.
2.1.4 Licensee's Basis for Relief The licensee's March 3, 1995, letter provided the following basis for use of Code Case N-416-1:
Pursuant to 10 CFR 50.55a(a}{3)(i), relief is requested on the basis that the proposed alternatives provide an acceptable level of quality and safety.
Due to the additional preparation required to safely accomplish the required System Hydrostatic Tests (at pressures above normal operating levels) after welded repairs and replacements on Code Class 1, 2, and 3 components, these tests present unusual difficulties and often hardship situations for Palisades Nuclear Plant.
Some of the specific problems typically encountered when preparing for and performing these test include:
- Complicated or abnormal valve~line-ups in 9rder to properly vent, fill, and isolate the component requiring testing.
- Relief valves with setpoints lower than the hydrostatic test pressure must be gagged or removed and blind flanged.
This process requires the draining and refilling of the system both prior to the test and prior to system restoration.
- Valves that are not normally used for isolation (e.g., normally open pump discharge valves) are often required to provide pressure isolation for an el~vated pressure hydrostatic test. These valves frequently require time consuming seat maintenance in order to obtain a leak tight pressure boundary.
- The radiation exposure to plant personnel involved in hydrostatic tests is high in comparison to operational pressure testing due to the large amount of time required to prepare the volume for testing
{i.e, installing relief valve gags, performing appropriate valve line-ups, completing valve maintenance, filling and venting, etc.).
The difficulties encountered in performing a hydrostatic pressure test are unreasonable when weighted against the benefits.
Industry experience, which is supported by Palisades' experience, shows that most through-wall leakage is detected during system operations as opposed to during elevated pressure tests such as ten-year or post maintenance system hydrostatic tests.
No leakage detection benefit is gained from the added challenge to the piping system provided by an elevated pressure hydrostatic test as compared to a system operational test.
The stresses experienced during a
'hydrostatic test do not include the significant stresses associated with the thermal growth and dynamic loading seen during a system operational test. Thus, the system is more likely to experience any through-wall leakage at operating conditions due to the combination of dynamic/thermal loading and the normal operating pressure parameters than during the careful, slow pressurization of a hydrostatic test.
The ASME Board of Nuclear Codes and Standards has approved Code Case N-416-1, "Alternative Pressure Test Requirements for Welded Repairs or Installation of Replacement Items by Welding, Class l, 2, and 3 Systems,Section XI, Division l," which incorporates the logic and Alternative Examinations contained within this justification.
It is Palisades' position that system pressure tests and NOE
[nondestructive examination] on Class 1, Class 2 and Class 3 systems and components in accordance with the requirements of Nuclear Code Case N-416-1, provides a level of quality and safety equivalent to, or greater than, that provided by the Code hydrostatic testing requirements.
2.1.5 Evaluation 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 NOE 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 has not been changed.
The hold times for these tests has either remained unchanged or increased.
The corrective actions with respect to removal of bolts from leaking bolted connections has been relaxed in the 1992 Edition, but use of this change 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 indicates that experience has demonstrated that leaks are not being discovered as a result of hydrostatic test pressures propagating a preexisting flaw through wall.
Experience indicates 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 once each refueling outage for Class 1 systems and each 40-rnonth 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 I and 2, but only requires a surface examination of the final weld pass in Code Class 3 piping components.
There are no ongoing NOE 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.
Considering 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 NOE 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. CPC's proposed alternative in sections (d} and (e} is equivalent to or exceeds the provision noted in the previous sentence and therefore is acceptable;
3.0 CONCLUSION
S With this provision applied to Code Class 3 components, 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 Palisades Plant, 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, with the provision as noted above, 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:
C. K. Battige Date:
DISTRIBUTION Docket File PUBLIC PD3-1 Rdg File W. Russell/F. Miraglia R. Zimmerman R. Spessard, D/DOTS J. Lieberman, D/OE E. Adensam J. Hannon C. Carpenter C. Jamerson M. Gamberoni C. Battige OGC E. Jordan, D/AEOD G. H i 11, IRM ( 2 )
ACRS (4)
OPA OC/LFDCB B. McCabe, EDO 017G-21 W. Kropp, DRP, RIII cc:
Plant Service lisf