ML062790182

Information in Response to the NRC Phone Call on 07/21/06 Re Request for Relief to Section 50.55a(g) of Title 10 of the Code of Federal Regulations

ML062790182
Person / Time
Site:	Palo Verde
Issue date:	09/28/2006
From:	Mauldin D Arizona Public Service Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
102-05575-CDM/SAB/RJR, TAC MC9627, TAC MC9628, TAC MC9629
Download: ML062790182 (4)

Text

kAPS A subsidiaryof Pinnacle West CapitalCorporation David Mauldin Mail Station 7605 Palo Verde Nuclear Vice President Tel: 623-393-5553 P0 Box 52034 Generating Station Nuclear Engineering Fax: 623-393-6077 Phoenix, Arizona 85072-2034 102-05575-CDM/SAB/RJR September 28, 2006 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001

References:

APS letter 102-05398-CDM/SAB/RJR, "Proposed Alternative to PVNGS' ASME Section XI Inservice Inspection Program for ASME Code Category B-F, B-J, C-F-I, and C-F-2 Piping (Relief Request 32)," dated January 16, 2006.

APS letter 102-05515-CDM/SAB/RJR, "Response to the NRC Request for Additional Information Regarding Risk-Informed Inservice Inspection Program Request (TAC NOS. MC9627, MC9628, AND MC9629)," dated June 10, 2006.

APS fetter 102-05559-CDM/SAB/RJR, "Response to the NRC Request for Additional Information Regarding Risk-Informed Inservice Inspection Program Request (TAC NOS. MC9627, MC9628, AND MC9629)," dated August 30, 2006.

SUBJECT:

Palo Verde Nuclear Generating Station (PVNGS)

Units 1, 2 and 3 Docket Nos. STN 50-528/529/530 Information in Response to the NRC Phone Call on July 21, 2006 (TAC NOS. MC9627, MC9628, AND MC9629)

Dear Sirs:

In the letters referenced above, Arizona Public Service (APS) submitted a proposed alternative and responses to requests for additional information associated with a request for relief to section 50.55a(g) of Title 10 of the Code of FederalRegulations (10 CFR). Specifically, APS proposed using a risk-informed (RI) Inservice Inspection (ISI) program as an alternative to the current ISI program requirements of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code of record for Palo Verde Nuclear Generating Station, Units 1, 2, and 3.

A member of the STARS (Strategic Teaming and Resource Sharing) Alliance Callaway a Comanche Peak 0 Diablo Canyon 0 Palo Verde

• South Texas Project

• Wolf Creek A04 7

NRC Document Control Desk Page 2 Information in Response to the NRC Phone Call on July 21, 2006 (TAC NOS. MC9627, MC9628, AND MC9629)

On July 21, 2006, APS and the NRC discussed the inspection frequency for nickel based alloy dissimilar metal welds currently listed in the risk-informed ISI Program relief request and the Risk Category 4 portion of the charging system. This letter documents the APS response to the questions asked by the NRC.

NRC Question 1:

How is APS going to address the inspection frequency for the nickel based alloy dissimilar metal welds currently listed in the risk-informed ISI Program relief request?

Are the inspection frequencies for these welds going to be consistent with the EPRI guidance?

APS Response:

A plant augmented inspection program is being implemented at Palo Verde in response to MRP-1 39, "Materials Reliability Program: Primary System Piping Butt Weld Inspection and Evaluation Guidelines." The requirements of MRP-139 will be used for the inspection and management of PWSCC susceptible dissimilar metal welds and will supplement the RI-ISI Program selection process. The RI-ISI Program will not be used to eliminate any MRP-139 requirements.

NRC Question 2:

In the June 10, 2006 response to the NRC request for additional information, it is stated that the risk category 4 portion of the charging system is located just beyond the affected region of the charging line that is potentially subjected to thermal transients when flow is restored after a loss of charging event. Please provide the thermal transient analysis and the criteria used to identify the boundary between the risk category 2 segment and the risk category 4 segment.

APS Response:

The basis for the Thermal Transient analysis for the charging line is provided in EPRI document number EPRI TR-104534-V2, "EPRI Fatigue Management Handbook, Volume 2 - Screening Criteria," December 1994.

The site specific analysis can be summarized in the following manner. In the case of the charging line under conditions of interruption and restoration of charging flow, there are two distinct regions for Thermal Transient evaluation. When flow is interrupted, hot RCS cold leg fluid will conservatively be expected to fill that portion of the line (through turbulent penetration and convection) which is vertically upward or horizontal off the RCS cold leg. Let us call this Region 1. Beyond the point where the line turns vertically downward, the line would not be heated by convection, and it is also remote enough

NRC Document Control Desk Page 3 Information in Response to the NRC Phone Call on July 21, 2006 (TAC NOS. MC9627, MC9628, AND MC9629)

(>90 ft. from RCS main loop) to not be within the effective range of turbulent penetration from the RCS cold leg, which is the only mechanism by which the line could potentially be heated in this configuration. Therefore, beyond the downward turn of the charging line, the piping would revert to approximately containment ambient temperature during any significant period of charging flow interruption. Let us call this Region 2. For purposes of conservatism, the weld on the vertical side of the first down-elbow is also included in Region 1.

Upon flow restoration, hot charging fluid would first enter the piping remote from the RCS (Region 2) at approximately containment ambient temperature, resulting in a thermal shock to this portion of the charging line. The region closer to the RCS cold leg (Region 1), heated to RCS cold leg temperature, would first encounter a "slug" of cold fluid from the containment ambient piping as it is forced ahead of the restored charging flow, and then almost immediately afterward would encounter the hot restored charging flow itself. This would result in a "double-shock" to Region 1. The Thermal Transient potential for each region must be evaluated separately.

Temperatures, flowrates and operating conditions are provided in the various plant references. The input parameters and calculated results for each of the two regions are provided below:

REGION 2 1 System CH CH/RC CH-E-005-BCAA-3" CH-E-005-BCAA-3" ch connection)

Example Line No. (+ branch connection)

Line Description Charging line Charging line Operating Condition Flow restoration Flow restoration Hot Fluid Source Charging flow Cold leg/charging flow Cold Fluid Source Cold slug Cold slug Hot Fluid Temp. (F) 450 554/450 Cold Fluid Temp. (F) 120 120 Pipe Material Stainless steel Stainless steel NPS (in) 3.0 3.0 Thickness (in) 0.438 0.438 Q allowable (gpm) 69.5 21.7 Q actual (gpm) 62.0 62.0 IT Concern NO YES

NRC Document Control Desk Page 4 Information in Response to the NRC Phone Call on July 21, 2006 (TAC NOS. MC9627, MC9628, AND MC9629)

The results show that Region 1, also known as Risk Segment X-CH-005, is susceptible to the Thermal Transient degradation mechanism due to the "double-shock" it encounters upon flow restoration, while Region 2, also known as Risk Segment X-CH-004, is not susceptible to thermal transients (TT).

The Risk Informed - Inservice Inspection Program is in the process of being updated (Living Program Update). Verification of the degradation mechanisms, boundaries and selections will be revalidated and updated where required.

This letter contains no new commitments and no revisions to existing commitments.

If you have any questions about this change, please telephone Thomas N. Weber at (623) 393-5764.

Sincerely, CDM/SAB/RJ R/gt cc: B. S. Mallett NRC Region IV Regional Administrator M. B. Fields NRC NRR Project Manager G. G. Warnick NRC Senior Resident Inspector for PVNGS