ML15114A431

Response to NRC Request for Additional Information for Relief Request 53

ML15114A431
Person / Time
Site:	Palo Verde
Issue date:	04/24/2015
From:	Mims D Arizona Public Service Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
102-07042-DCM/DCE
Download: ML15114A431 (13)

Text

10 CFR 50.SSa I

(.laps DWIGHT C. MIMS Senior Vice President, Nuclear Regulatory & Oversight I*

I Palo Verde Nuclear Generating Station P.O. Box 52034 Phoenix, AZ 85072 Mail Station 7605 102-07042-DCM/DCE Tel 623 393 5403 April 24, 2015 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001

Reference:

1. Arizona Public Service Company (APS) letter number 102-07034, Palo Verde Nuclear Generating Station Unit 3, Docket No. STN 50-530, American Society of Mechanical Engineers (ASME) Code,Section XI, Request for Approval of an Alternative to Flaw Removal

- Relief Request 53, dated April 17, 2015

2. APS letter number 102-07037, Palo Verde Nuclear Generating Station Unit 3, Docket No. STN 50-530, Transmittal of Proprietary Documents for Relief Request 53, dated April 17, 2015

3. NRC email Palo Verde Unit 3 - Request for Additional Information Regarding Relief Request 53, dated April 23, 2015

Subject:

Palo Verde Nuclear Generating Station (PVNGS)

Unit 3 Docket No. 50-530 APS Response to NRC Request for Additional Information (RAI) for Relief Request 53 On April 17, 2015, pursuant to 10 CFR 50.55a(z)(l), Arizona Public Service Company (APS) requested NRC approval of Relief Request 53 (References 1 and 2). Relief Request 53 proposed an alternative to the ASME Code requirements of Section XI related to flaw indications that were identified in Unit 3 reactor coolant pump 2A suction pressure instrument nozzle on April 8, 2015. Specifically, APS is proposing a half-nozzle repair and flaw evaluation which provides an acceptable level of quality and safety as an alternative to the IWA-4421 requirements for flaw removal. The duration of this relief request is for one operating fuel cycle.

In an email dated April 23, 2015 (Reference 3), NRC staff requested additional information to support the review of Relief Request 53.

This letter transmits APS responses to the RAI. No commitments are being made to the NRC by this letter.

A member of the STARS (Strategic Teaming and Resource Sharing) Alliance Callaway

• Diablo Canyon

• Palo Verde

• Wolf Creek

ATTN: Document Control Desk U.S. Nuclear Regulatory Commission APS Response to NRC Request for Additional Information for Relief Request 53 Page 2 Should you need further information regarding this relief request, please contact Thomas Weber, Regulatory Affairs Department Leader at (623) 393-5764.

Sincerely, DCM/DCE/hsc

Enclosure:

APS Response to NRC Request for Additional Information for Relief Request 53 cc: M. L. Dapas NRC Region IV Regional Administrator M. M. Watford NRC NRR Project Manager for PVNGS C. A. Peabody NRC Senior Resident Inspector for PVNGS

Enclosure APS Response to NRC Request for Additional Information for Relief Request 53 ATTACHMENTS - Isometric Sketches for NRC Question 3

Enclosure APS Response to NRC Request for Additional Information for Relief Request 53 Introduction On April 17, 2015, pursuant to 10 CFR 50.55a(z)(1), Arizona Public Service Company (APS) requested NRC approval of Relief Request 53 (References 1 and 2 to this Enclosure). Relief Request 53 proposed an alternative to the ASME Code requirements of Section XI related to flaw indications that were confirmed by visual examination on the Unit 3 reactor coolant pump (RCP) 2A suction pressure instrument nozzle on April 8, 2015.

Specifically, APS is proposing a half-nozzle repair and flaw evaluation which provides an acceptable level of quality and safety as an alternative to the IWA-4421 requirements for flaw removal. The duration of this relief request is for one operating fuel cycle.

In an email dated April 23, 2015 (Reference 3 to this Enclosure), NRC staff requested additional information to support the review of Relief Request 53.

Each request for additional information (RAI) question is listed below with a response.

Each RAI question pertains to a particular document provided as part of Relief Request 53 and are listed under a heading for the respective document.

Letter dated April 17, 2015, American Society of Mechanical Engineers (ASME)

Code,Section XI, Request for Approval of an Alternative to Flaw Removal -

Relief Request 53, Non-Proprietary (Publically available)

NRC Question 1 Section 1, ASME Code Components Affected, on Page 3 of the relief request identifies the pressure instrument nozzle being classified as Examination Category B-P (Class 1 PWR Components Containing Alloy 600/82/182) and Code Item Number B15.205. However, in the ASME Code,Section XI, Table IWB-2500-1, Code Item number B15.205 does not belong to or match with Examination Category B-P. Also, Class 1 pressure retaining dissimilar metal welds in vessel nozzles should be classified as Examination Category B-F, not B-P. Item Number B15.205 does appear in Table 1, Examination Categories, of Code Case N-722-1, but not in the ASME Code. Clarify the exact Examination Category and Item Number of the subject pressure instrument nozzle and provide the reference.

APS Response:

The information for the relief request is updated as follows:

Examination Category: ASME Code Case N-722-1, Class 1 PWR Components Containing Alloy 600/82/182 Code Item Number: B15.205, Cold Leg Instrument Connections 1

Enclosure APS Response to NRC Request for Additional Information for Relief Request 53 The 3rd Inspection Interval, Inservice Inspection Summary Manual, PVNGS Unit 3, (Reference 4 to this Enclosure) places the RCP 2A suction pressure instrument nozzle under the scope of the examination category for ASME Code Case N-722-1 Item B.15-205. Examination category B-P applies to the suction pressure instrument nozzle with respect to the pressure test program, but not visual examinations related to Code Case N-722-1.

NRC Question 2 The design of the half nozzle repair includes a gap of 0.06 inch between the remnant nozzle and the new nozzle. Discuss calculations that were made to ensure that the 0.06 inch gap is sufficient for the thermal expansion of the remnant nozzle and new nozzle. If no calculations were performed, provide justification.

APS Response:

The minimum gap specified between the replacement nozzle and the nozzle remnant is based on the thermal expansion coefficient of both the replacement and remnant nozzle (7.865 x 10-6 in/in/°F for Inconel). The thermal growth of the two pieces will be less than 25 percent of the minimum gap at a maximum operating temperature of 565°F, which ensures a sufficient gap between the remnant and new nozzles.

NRC Question 3 Provide a piping isometric showing the locations and distances of pipe hangers and restraints along the pressure instrument line from the instrument nozzle attached to the reactor coolant pump to the first anchor.

APS Response:

Two drawings, Drawing A and Drawing B, are provided in Attachment 1, Isometric Sketches for NRC Question 3. These identified sections provide locations and distances to the pipe support, shown on Drawing B as Node 125, along the pressure instrument line which terminates at the flex hose (transmitter connection). - APS Response to NRC Request for Additional Information (RAI),

dated April 14, 2015 NRC Question 4 The licensee's response to NRC's RAI Question No. 3(c) did not address the frequency of the boric acid walkdown for the subject repaired instrument nozzle for the future inservice inspections.

a. Discuss how often the repaired instrument nozzle will be examined in future inservice inspections.

2

Enclosure APS Response to NRC Request for Additional Information for Relief Request 53

b. After the repair, discuss under which Examination Category and Examination Item will the new J-groove weld be classified in accordance with the ASME Code,Section XI, Table IWB-2500-1.

APS Response:

The RCP 2A suction pressure instrument nozzle is included in the scope of the boric acid walkdown procedure, performed during each refueling outage. These walkdowns are governed by the Boric Acid Corrosion Control Program and are not part of the Inservice Inspection Program.

a. Inservice Inspection Program requirements for bare metal examinations for ASME Code Case N-772-1 do not apply to the repaired, external nozzle and J-groove weld because they use Alloy 690 and 52M materials.

b. After the repair, the new J-groove weld will not be categorized within the scope of Code Case N-722-1 (see response to NRC Question 1), but will remain categorized as B-P in accordance with Table IWB-2500-1 with respect to the pressure test program.

NRC Question 5 In the PCI Quality Assurance Traveler on Page 12 of 18, Sequence Number 9.1.22 states that APS to perform liquid penetrant examination of all machined surfaces of the replacement nozzle. Sequence Number 9.1.25 instructs APS to perform liquid penetrant examination of weld preparation area on the casing of the reactor coolant pump. After a portion of the original nozzle is removed from the bore of the safe end, clarify whether the inside diameter surface of the bore will be examined by liquid penetrant testing prior to inserting the new Alloy 690 nozzle. If not, discuss how to ensure the bore contains no imperfections.

APS Response:

The internal bore of the safe end nozzle penetration outer half was reamed to increase the bore diameter. In accordance with the traveler, the new J-groove weld preparation (one-half inch depth) received a liquid penetrant examination. The adjacent one-half inch of the bore beyond the weld preparation area received a liquid penetrant examination in accordance with APS procedures. The entire machined surface of the bore area received a visual examination. No imperfections were identified in these examinations.

3

Enclosure APS Response to NRC Request for Additional Information for Relief Request 53 Letter dated April 17, 2015, Transmittal of Proprietary Documents for Relief Request 53, Proprietary Attachments (Non-public) - Westinghouse Document DAR-MRCDA-15-6-P, Rev. 1, Palo Verde Unit 3 RCS Cold Leg Alloy 600 Small Bore Nozzle Repair (Non-public)

NRC Question 6 Page 8 states that the fatigue usage factor for the cold leg piping is W (proprietary information). Discuss whether a usage factor of W is for the one cycle or for 40 years of operation.

APS Response:

The fatigue usage factor for the cold leg piping is based on 40 years of operation. - Westinghouse Calculation CN-MRCDA-15-13, Rev. 0, Qualification of Palo Verde Unit 3 Reactor Coolant Pump Replacement Instrumentation Nozzle (Non-public)

NRC Question 7 The licensee uses the stress analysis that Westinghouse performed for Plant X to apply to Palo Verde, Unit 3. Figure 4-1, Plant X and Palo Verde Unit 3 Instrumentation Nozzle Layout, on Page 13 presents the location of the new J-groove weld at Palo Verde and the analyzed J-groove weld at Plant X. The J-groove weld at Plant X is located inside surface of the pipe whereas the new J-groove weld at Palo Verde is located at the outside surface of the safe end. The licensee stated that the impact of thermal and pressure transient loads will be less significant than those on the Plant X attachment weld. Discuss the impact of the different weld locations on all analyses and calculations involved in the repaired instrument nozzle at Palo Verde.

APS Response:

The weld at Plant X is subjected to higher thermal and operating transients than the PVNGS location because it is located at the inside of the safe end. Thus, the fatigue evaluations in Plant X for 40 years bound PVNGS for 18 months at the weld and nozzle locations.

However, the mechanical loads from operation, deadweight and seismic as well as external nozzle loads are higher in the PVNGS nozzle and, as such, a PVNGS specific analysis was performed to size the weld in accordance with the ASME Code. The nozzle was evaluated based on a comparison to the Plant X nozzle since both are identical in terms of geometry and materials. The closed form solutions for Plant X were used in the evaluations; however, the variables were modified to account for the difference in weld locations and the difference in loads.

4

Enclosure APS Response to NRC Request for Additional Information for Relief Request 53 NRC Question 8 Clarify which results of Plant X analysis are applicable to the subject instrument nozzle and which results of Plant X analysis are not applicable. Clarify which analysis is performed using the plant-specific parameters from Palo Verde.

APS Response:

Thermal stresses and fatigue usage results from the Plant X evaluation are applicable and bounding for the PVNGS Unit 3 instrumentation nozzle and attachment weld. The primary stresses for the PVNGS Unit 3 instrumentation nozzle and attachment weld were analyzed using Palo Verde mechanical loads and parameters. See response to NRC Question 7 for further clarification.

NRC Question 9 On Page 18, Table 4-2, Nozzle Mechanical Loads, shows that Fx and Fz have zero load for the normal condition, whereas for the faulted condition, Fx and Fz have 19 pounds (lbs) each.

a. Confirm that the 19 lbs for the faulted condition are based on seismic loading.

b. Clarify why Fx and Fz have zero load for the normal condition.

c. Discuss why the nozzle mechanical loads are so low considering that five mechanical loads are applied to the nozzle, as discussed on Page 13 and 14.

APS Response:

a. The 19 lbs noted on Table 4-2 for Fx and Fz for the faulted condition are based on seismic loading.

b. The normal condition consists of deadweight and thermal loads. There is negligible differential movement between the small bore pipe at the support location and nozzle because the pipe is supported from the main reactor coolant piping (tie back support) and has enough flexibility to accommodate thermal growth. Therefore, the thermal loads (Fx and Fz) are negligible and considered to be zero in the calculation.

c. The five loads discussed on pages 13 and 14 consist of nozzle mechanical and four other loads. The nozzle mechanical loads are low due to the small mass of the piping and attached valve. Additionally, thermal loads are negligible as described in the answer to NRC Question 9.b.

NRC Question 10 On Page 24, Table 5-6, Attachment Weld Input Loads, presents an axial load of 0.8 lbf on the new weld for the normal condition. Explain why the axial load is so low.

5

Enclosure APS Response to NRC Request for Additional Information for Relief Request 53 APS Response:

The axial loads consist of deadweight and thermal constituents which are negligible due to the small weight of the nozzle (less than 3 lbs) and flexibility of the pipe as discussed in the response to NRC Question 9. - Westinghouse Calculation CN-PAFM-15-20, Rev. 2, Palo Verde Unit 3 RCS Cold Leg Alloy 600 Small Bore Nozzle Repair Transient Stress and Fracture Mechanics Evaluation for One Cycle Operation (Non-public)

NRC Question 11 Page 10 states that the corrosion allowance for the bore of the subject nozzle should be larger than the corrosion allowance (X inches, proprietary information) for the hot leg nozzles.

a. Clarify why the cold leg corrosion allowance for the bore is larger than the corrosion allowance for the hot leg nozzles.

b. It appears that the corrosion allowance is rather large such that the bore may not provide any friction to resist the nozzle ejection load. Discuss whether the new J-groove weld can support the entire nozzle ejection load without the support of the friction from the ID surface of the bore.

APS Response:

a. The corrosion allowance of the reactor coolant pump suction safe end and the hot leg are based on their geometries. The differences in geometry (radius and wall thickness) are why the allowance is larger for the reactor coolant pump suction safe end than the hot leg. The PVNGS suction safe end corrosion allowance was determined in accordance with the ASME Code in calculation CN-MRCDA-15-13, Table 5-5 (Attachment 2 to Reference 2 of this Enclosure), and is larger than the 0.23 inch hot leg corrosion allowance. For conservatism, a reduced value equal to the hot leg corrosion allowance (0.23 inch) was utilized.

b. The calculation did not credit friction between the bore and the nozzle to resist the nozzle ejection load. The evaluation of the attachment weld in CN-MRCDA-15-13 included the impact of blow-off load on the nozzle and demonstrated satisfactory results.

NRC Question 12 Page 15 states that the allowable flaw size evaluation performed for a hot leg nozzle repair would be conservatively representative for the Palo Verde Unit 3 RCP suction safe end instrumentation nozzle. Provide the allowable flaw size associated with the RCP suction safe end.

6

Enclosure APS Response to NRC Request for Additional Information for Relief Request 53 APS Response:

The allowable flaw size associated with the RCP suction safe end was not calculated for this one cycle relief request. Instead, the flaw evaluation in calculation CN-PAFM-15-20 (Attachment 3 to Reference 2 of this Enclosure) used the hot leg piping critical crack length determined in Westinghouse Calculation CN-CI-02-71 that was previously reviewed by the NRC as part of APS Relief Request 31, Revision 1 (Reference 5 to this Enclosure). This value for critical crack flaw size (see Tables 5-1 and 5-2 of Attachment 1 to Reference 2 of this Enclosure) conservatively bounds the PVNGS Unit 3 RCP suction safe end piping allowable value. This is due to the hot leg loads and corresponding cross sectional properties resulting in higher stresses and stress intensity values at a hypothetical crack(s) than at the cold leg.

Further, hot leg fracture toughness properties at RTNDT = 60°F were used in the evaluation while the cold leg fracture toughness properties would be determined at RTNDT = 40°F, which adds margin.

References

1. Arizona Public Service Company (APS) letter number 102-07034, Palo Verde Nuclear Generating Station Unit 3, Docket No. STN 50-530, American Society of Mechanical Engineers (ASME) Code,Section XI, Request for Approval of an Alternative to Flaw Removal - Relief Request 53, dated April 17, 2015

2. APS letter number 102-07037, Palo Verde Nuclear Generating Station Unit 3, Docket No. STN 50-530, Transmittal of Proprietary Documents for Relief Request 53, dated April 17, 2015

3. NRC email, Palo Verde Unit 3 - Request for Additional Information Regarding Relief Request 53, dated April 23, 2015

4. 3rd Inspection Interval, Inservice Inspection Summary Manual, PVNGS Unit 3, Revision 3, August 2013

5. NRC letter Palo Verde Nuclear Generating Station, Units 1, 2, and 3 - Relief Request No. 31, Revision 1, Re: Proposed Alternative Repair for Reactor Coolant System Hot-Leg Alloy 600 Small-Bore Nozzles, dated September 12, 2006 Agencywide Documents Access and Management System (ADAMS) Accession No. ML062300333 Attachments - Isometric Sketches for NRC Question 3 7

Enclosure APS Response to NRC Request for Additional Information for Relief Request 53 Attachment 1 Isometric Sketches for NRC Question 3

Digitally signed by Harris, Harris, Dianne R(ZA8953)

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