RS-12-064, Relief Request 14R-19 Associated with the Reactor Pressure Vessel Nozzle Repairs

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Relief Request 14R-19 Associated with the Reactor Pressure Vessel Nozzle Repairs
ML12100A012
Person / Time
Site: Quad Cities Constellation icon.png
Issue date: 04/06/2012
From: Simpson P
Exelon Generation Co, Exelon Nuclear
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
RS-12-064
Download: ML12100A012 (8)
v • d • e


Text

Exelon Generation Company, LLC www.exeloncorp.com 4300 Winfield Road Nuclear Warrenville, IL 60555 RS-12-064 10 CFR 50.55a April 6, 2012 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555-0001 Quad Cities Nuclear Power Station, Unit 2 Renewed Facility Operating License No. DPR-30 NRC Docket No. 50-265

Subject:

Relief Request 14R-19 Associated with the Reactor Pressure Vessel Nozzle Repairs In accordance with 10 CFR 50.55a, "Codes and standards," paragraph (a)(3)(i), Exelon Generation Company, LLC (EGC), hereby requests NRC approval of the attached relief request associated with the Fourth Inservice Inspection (ISI) Interval for Quad Cities Nuclear Power Station (QCNPS), Unit 2. The fourth interval of the QCNPS ISI program complies with the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code,Section XI, 1995 Edition with addenda through 1996.

During a recent pressure test of the reactor pressure vessel, one instrument penetration, N-11 B, was found to have approximately 60 drops per minute of leakage. EGC intends to repair the penetration by installing a welded pad using Ambient Temperature Temper Bead (ATTB) welding in accordance with ASME Code Case N -638-4, "Similar and Dissimilar Metal Welding Using Ambient Temperature Machine GTAW Temper Bead Technique,Section XI, Division I."

In support of the flaw evaluation and application of applicable acceptance criteria, ASME Code Paragraphs IWB-3420 and IWB-3600 require characterization of the flaw in the penetration.

Additionally, if a component is accepted for continued service in accordance with IWB -3142.4, the areas containing flaws or relevant conditions are required to be re -examined during the next three inspection periods. These subsequent examinations are intended to identify growth of the actual flaw over time.

Currently there is not a qualified or demonstrated technique to perform volumetric non-destructive examination (NDE) of the partial penetration weld in this configuration that can be used to accurately characterize the location, orientation, or size of a flaw in the weld. As an alternative to performing the NDE required to characterize the flaw in penetration N-11 B, EGC proposes analyzing a maximum postulated flaw that bounds the range of flaw sizes that could exist in the J -groove weld and nozzle.

U.S. Nuclear Regulatory Commission April 6, 2012 Page 2 In accordance with 10 CFR 50.55a(a)(3)(i), the proposed alternatives may be approved by the NRC provided an acceptable level of quality and safety are maintained. EGC concludes the proposed alternatives meet this requirement.

EGC requests approval of the proposed alternative (i.e., attached Relief Request Number 14R-1 9) in order to support the return to service from the current QCNPS, Unit 2 refueling outage (Q2R21). Unit 2 startup is currently anticipated to commence on April 16, 2012.

There are no regulatory commitments contained within this letter.

Should you have any questions concerning this letter, please contact Mr. Joseph A. Bauer at (630) 657-2804.

Patrick R. Simpson Manager - Licensing Exelon Generation Company, LLC

Attachment:

10 CFR 50.55a Request Number 14R-19

ATTACHMENT 10 CFR 50.55a Request Number I4R-19 Criteria - Alternative Provides an Acceptable Level of Quality and Safety (10 CFR 50.55a(a)(3)(i))

Page 1 of 6 1.0 ASME CODE COMPONENTS AFFECTED:

Code Class: 1 Component Number: Reactor Pressure Vessel (RPV) Penetration N-11B Examination Category: B-P Item Number: B15.10

Description:

Reactor Pressure Vessel Water Level Instrument Penetration - 2" NPS 2.0 APPLICABLE CODE EDITION AND ADDENDA:

The code of record for the fourth 10-year Inservice Inspection Program interval at Quad Cities Nuclear Power Station, Unit 2 (QCNPS) is the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel (B&PV) Code,Section XI, 1995 Edition through 1996 Addenda.

Code of Construction (RPV): ASME Section III, 1965 Edition through Summer 1965 Addenda.

Code of Construction (Instrument Penetration Nozzle): ASME Section III, 1965 Edition through Summer 1969 Addenda.

3.0 APPLICABLE CODE REQUIREMENT:

The specific Code requirements for which use of the proposed alternative is being requested are as follows:

Flaw Removal

  • IWA-5250(a)(3) states "Components requiring correction shall have repair/replacement activities performed in accordance with IWA-4000."
  • IWA-4410(a) states "Repair/replacement activities shall be performed in accordance with the Owner's Requirements and the original Construction Code of the component or system, except as provided in IWA-4410(b), (c), and (d)."
  • The applicable requirements of the Construction Code required by IWA-4410(a) for the removal of defects.
  • N-528 requires repair of weld defects including removal of defects detected by leakage tests.
  • IWA-4611.1 states in part "Defects shall be removed or reduced in size in accordance with this Paragraph."

ATTACHMENT 10 CFR 50.55a Request Number I4R-19 Criteria - Alternative Provides an Acceptable Level of Quality and Safety (10 CFR 50.55a(a)(3)(i))

Page 2 of 6 Flaw Evaluation

  • IWB-3522.1 states "relevant conditions that may be detected during the conduct of system pressure tests shall require correction to meet the requirements of IWB-3142 and IWA-5250 prior to continued service "
1. IWB-3142.1(b) states "A component whose visual examination detects the relevant conditions described in the standards of Table IWB-3410-1 shall be unacceptable for continued service, unless such components meet the requirements of IWB-3142.2, 3142.3, or 3142.4."
2. IWB-3142.4 states "A component containing relevant conditions is acceptable for continued service if an analytical evaluation demonstrates the component's acceptability. The evaluation analysis and evaluation acceptance criteria shall be specified by the Owner. A component accepted for continued service based on analytical evaluation shall be subsequently examined in accordance with IWB-2420(b) and (c)."
  • IWA-3300(a) states in part "Flaws detected by the preservice and inservice examinations shall be sized"
  • IWA-3300(b) states in part "Flaws shall be characterized in accordance with IWA-3310 through IWA-3390, as applicable"
  • IWB-3610(b) states "For purposes of evaluation by analysis, the depth of flaws in clad components shall be defined in accordance with Fig. IWB-3610-1."
  • IWB-3420 states "Each detected flaw or group of flaws shall be characterized by the rules of IWA-3300 to establish the dimensions of the flaws. These dimensions shall be used in conjunction with the acceptance standards of IWB-3500."

4.0 REASON FOR REQUEST:

During the present QCNPS, Unit 2 refueling outage and as a result of leakage indications on the reactor pressure vessel penetration N-11B, Exelon Generation Company, LLC (EGC) will partially replace this existing nozzle assembly with a nozzle penetration that is resistant to Intergranular Stress Corrosion Cracking (IGSCC). A welded pad will be applied to the outside surface (OD) of the RPV using IGSCC resistant nickel Alloy 52M (ERNiCrFe-7 or -7A) filler metals and will be welded using the machine gas tungsten arc welding (GTAW) ambient temperature temper bead (ATTB) welding technique. An IGSCC resistant nozzle will be attached to the new weld pad with a partial penetration weld using a non-temper bead manual welding technique. The original partial penetration attachment weld and a remnant of the original nozzle will remain in place. A failure assessment is planned to be completed prior to startup to demonstrate the acceptability of leaving the original partial penetration attachment weld, with a maximum postulated flaw, in place for one cycle.

IWA-4410 and IWA-4611 contain requirements for the removal of, or reduction in size of defects. The defect on N-11B will not be removed; therefore, relief is sought from these requirements.

ATTACHMENT 10 CFR 50.55a Request Number I4R-19 Criteria - Alternative Provides an Acceptable Level of Quality and Safety (10 CFR 50.55a(a)(3)(i))

Page 3 of 6 IWB-3400 and IWB-3600 were written with the expectation that NDE techniques such as ultrasonic testing (UT) would be used to determine the flaw size and shape.

In support of the flaw evaluation and application of applicable acceptance criteria, the ASME Code paragraphs IWB-3420 and IWB-3600 require characterization of the flaw in the leaking penetration. Currently, there is not a qualified or demonstrated technique to perform volumetric non-destructive examination (NDE) of the partial penetration weld in this configuration that can be used to accurately characterize the location, orientation, or size of a flaw in the weld.

The ASME Code Section XI IWB-2420(b) and (c) require that if a component is accepted for continued service in accordance with IWB-3132.3 or IWB-3142.4, the areas containing flaws or relevant conditions shall be reexamined during the next three inspection periods.

These subsequent examinations are intended to identify growth of the actual flaw over time. Currently, there is not a qualified or demonstrated technique to perform volumetric NDE of the partial penetration weld in this configuration that can be used to accurately determine flaw growth.

The proposed repair will be performed by installing a welded pad using ATTB welding in accordance with ASME Code Case N-638-4. The NRC has conditionally approved ASME Code Section XI Code Case N-638-4 to allow ambient temperature temper bead welding of ferritic materials without the requirement for preheat or post-weld heat treatment.

5.0 PROPOSED ALTERNATIVE AND BASIS FOR USE:

Pursuant to 10 CFR 50.55a(a)(3)(i), EGC proposes the following alternatives to the ASME Code Section XI requirements specified in Section 4 above.

A. As an alternative to flaw removal or reduction in size to meet the applicable acceptance standards, EGC proposes to implement the OD repair of the reactor vessel instrument nozzle N-11B utilizing an OD weld pad as described below in the discussion of the repair of nozzle penetrations.

B. As an alternative to performing the NDE required to characterize the flaw under IWB-3420 and IWB-3610(b) in penetration N-11B, EGC proposes analyzing a maximum postulated flaw that bounds the range of flaw sizes that could exist in the J-groove weld and nozzle.

C. As an alternative to performing the subsequent NDE required by IWB-3142.4 in accordance with IWB-2420(b) and (c) to assess potential growth of the flaw in penetration N-11B, EGC proposes analyzing a maximum postulated flaw that bounds the potential growth of the existing flaw.

ATTACHMENT 10 CFR 50.55a Request Number I4R-19 Criteria - Alternative Provides an Acceptable Level of Quality and Safety (10 CFR 50.55a(a)(3)(i))

Page 4 of 6 BASIS A. Background The QCNPS, Unit 2 reactor vessel is manufactured from SA-302, Grade B, modified by Code Case 1339, carbon steel that is clad with stainless steel. The reactor vessel Water Level Instrument penetrations are fabricated with Alloy 600 components.

IGSCC of Alloy 600 components and welds exposed to BWR cooling water has been observed in the nuclear industry over the recent past. In particular, dissimilar metal welds (DMWs) made with nickel Alloy 182 weld metal exposed to elevated operating temperatures, such as nozzle J-groove welds, pose a heightened propensity to IGSCC.

During the current refueling outage (Q2R21), EGC discovered a leak in a Water Level Instrument penetration nozzle N-11B located on the reactor vessel upper shell. The examination that detected the defect consisted of a visual examination in which active leakage was observed at the nozzle interface with the reactor vessel OD during the Class 1 System Leakage Test. This observation necessitates the repair of this Water Level Instrument nozzle using the methodology proposed herein.

B. Repair of Nozzle Penetrations EGC will replace this existing nozzle assembly with a nozzle penetration that is resistant to IGSCC, meetsSection XI and Code Case N-638-4 as conditionally approved by the NRC in Regulatory Guide 1.147, Revision 16. See Figure 1 for a typical RPV water level instrument nozzle repair. A welded pad will be applied to the OD of the RPV using IGSCC resistant nickel Alloy 52M (ERNiCrFe-7 or -7A) filler metals and will be welded using the machine GTAW ATTB welding technique. The IGSCC resistant nozzle will be attached to the new weld pad with a partial penetration weld using a non-temper bead manual welding technique. The original partial penetration attachment weld and a remnant of the original nozzle will remain in place.

A failure assessment is planned to be completed prior to startup to demonstrate the acceptability of leaving the original partial penetration attachment weld, with a maximum postulated flaw, in place for one cycle.

C. Flaw Evaluation A flaw evaluation in accordance with IWB-3610 will be performed for one cycle of operation based on the following:

  • Conservatively assume that the entire J-groove weld is flawed;
  • The postulated initial flaw will be increased by a fixed amount to account for fatigue crack growth over one cycle of operation based on analytical experience;
  • Weld residual stresses will conservatively be based on room temperature yield strength of the weld material; and
  • The evaluation will use the available pressure and thermal stresses from the analysis of record.

ATTACHMENT 10 CFR 50.55a Request Number I4R-19 Criteria - Alternative Provides an Acceptable Level of Quality and Safety (10 CFR 50.55a(a)(3)(i))

Page 5 of 6 Qualification beyond one cycle will be performed based on detailed residual stress analysis and fatigue crack growth analysis.

Inservice inspection of the repaired nozzle, which is a partial penetration, will be examined in accordance with Table IWB-2500-1, Category B-P, Item B15.10.

D. Conclusion 10 CFR 50.55a(a)(3) states: "Proposed alternatives to the requirements of paragraphs (c), (d), (e), (f), (g), and (h) of this section, or portions thereof, may be used when authorized by the Director, Office of Nuclear Reactor Regulation The applicant shall demonstrate that:

(i) The proposed alternatives would provide an acceptable level of quality and safety; or (ii) Compliance with the specified requirements of this section would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety."

EGC concludes that the proposed alternatives of this request provide an acceptable level of quality and safety. The weld pad on the reactor vessel will be installed using Nickel Alloy 52M filler metal using a qualified ATTB welding procedure. The RPV penetration will be replaced with an IGSCC resistant nozzle welded to the OD of the reactor vessel with Alloy 52M. The flaw evaluation, previously discussed in this relief request, will show that the reactor vessel is acceptable without removal of the original nozzle remnant and partial penetration weld. Use of a maximum postulated flaw in the flaw evaluation is an acceptable alternative to NDE characterization of the actual flaw at this time, and in place of future NDE. Therefore, EGC requests that the NRC authorize the proposed alternative in accordance with 10 CFR 50.55a(a)(3)(i).

6.0 DURATION OF PROPOSED ALTERNATIVE:

Relief is requested for the duration of QCNPS, Unit 2 Cycle 22 which is currently scheduled to start on April 16, 2012.

7.0 PRECEDENTS

A similar relief request was previously approved for Arkansas Nuclear One, Unit 1. Fourth ISI Interval Relief Request ANO1-R&R-013, was authorized for use by the NRC in a Safety Evaluation dated January 10, 2011.

ATTACHMENT 10 CFR 50.55a Request Number 14R-19 Criteria - Alternative Provides an Acceptable Level of Quality and Safety (10 CFR 50.55a(a)(3)(i))

Page 6 of 6 Figure 1 Typical Reactor Pressure Vessel Water Level Instrument Nozzle Repair Detail C

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