DCL-15-038, Response to NRC Request for Additional Information Regarding Relief Request REP-SI - Part 2

Response to NRC Request for Additional Information Regarding Relief Request REP-SI - Part 2

ML15089A594
Person / Time
Site:	Diablo Canyon
Issue date:	03/30/2015
From:	Allen B Pacific Gas & Electric Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
DCL-15-038
Download: ML15089A594 (24)

Text

Pacific Gas and Electric Company Barry S. Allen Diablo Canyon Power Plant Vice President, Nuclear Services Mail Code 104/6 P. D. Box 56 Avila Beach, CA 93424 March 30, 2015 805.545.4888 Internal: 6 91.4888 PG&E Letter DCL-15-038 Fax: 805.545.6445 U.S. Nuclear Regulatory Commission 10 CFR 50.55a ATTN: Document Control Desk Washington, DC 20555-0001 Docket No. 50-275, OL-DPR-80 Docket No. 50-323, OL-DPR-82 Diablo Canyon Power Plant Unit 1 and Unit 2 Response to NRC Request for Additional Information Regarding Relief Request REP-SI - Part 2

References:

1. PG&E Letter DCL-14-060, "ASME Section Xllnservice Inspection Program Request for Alternative REP-SI: Proposed Alternative to Requirements for Repair/Replacement Activities for Certain Safety Injection Pump Welded Attachments," dated July 21, 2014 (ML14202A613)

2. NRC Letter, "Request for Additional Information -lnservice Inspection Request for Alternative REP-SI," dated December 23, 2014

3. PG&E Letter DCL-15-021, "Response to NRC Request for Additional Information Regarding Relief Request REP-SI," dated February 5, 2015 (ML15036A606)

Dear Commissioners and Staff:

In Reference 1, Pacific Gas and Electric Company (PG&E) submitted, "Relief Request for Alternative REP-SI for Diablo Canyon Power Plant Units 1 and 2," for NRC approval.

In Reference 2, the NRC Staff provided a request for additional information (RAI) via letter dated December 23, 2014. In Reference 3, PG&E submitted responses to seven out of the ten RAI questions. Enclosure 1 to this letter provides PG&E's responses to the remaining three RAI questions.

The relief request is further revised to include the results from carbon content measurements of the subject welds that were completed in February 2015. The revised version of the relief request is included in Enclosure 2 to this letter. The following three reports that were included in Reference 1 are current, still valid, A member of the STARS (Strategic Teaming and Resource Sharing) Alliance Callaway

• Diablo Canyon

• Palo Verde

• Wolf Creek

Document Control Desk PG&E Letter DCL-15-038 March 30, 2015 Page 2 and applicable to the revised relief request that is included in Enclosure 2:

• Weld Procedure Specification Number 149

• PG&E ATS Report 420DC-14.20: Welding Procedure Qualification Record (PQR) 771 and Associated Documents

• SIA Report No. 1301620.402: Stress and Fracture Mechanics Evaluation of Type 410 Stainless Steel Weldments in Safety Injection Pumps at Diablo Canyon Power Plant (Revision 2)

The photographs of vent and drain connections of safety injection pumps that were included in Reference 3 are also applicable to the revised relief request that is included in Enclosure 2.

PG&E makes two new regulatory commitments in this submittal (as defined by NEI 99-04) to be implemented following NRC authorization of this Relief Request.

The commitments are summarized in Attachment 1 to Enclosure 1.

If you have any questions or require additional information, please contact Mr. Philippe Soenen at (805) 545-6984.

Sincerely, JJ~

• 5.~

Barry S. Al~n Vice President, Nuclear Services rntt/4231/50600119 Enclosures cc: Diablo Distribution cc/enc: Marc L. Dapas, NRC Region IV Administrator Thomas R. Hipschman, NRC Senior Resident Inspector Siva P. Lingam, NRC Project Manager Gonzalo L. Perez, Branch Chief, California Department of Public Health State of California, Pressure Vessel Unit A member of the STARS (Strategic Teaming and Resource Sharing) Alliance Callaway

• Diablo Canyon

• Palo Verde

• Wolf Creek

Enclosure 1 PG&E Letter DCL-15-038 PG&E Response to NRC Request for Additional Information Regarding Relief Request REP-S I - Part 2 NRC Question RAI-EVIB 1.0:

The relief request is based on the premise that existing Sl pump vent and drain socket welds may be determined acceptable as-is for continued service. However, the possibility exists that all vent and drain socket welds could fail on an Sl pump. To properly evaluate the relief request, the NRC staff requests that the licensee describe:

(a) The safety significance if all vent and drain weld connections are severed on a single Sl pump.

(b) In case of failure of all vent and drain weld connections on a single Sl pump, please explain if the safety function of nearby equipment and personnel will be affected.

PG&E Response:

The response to this question is presented in four parts. Part 1 responds to both (a) and (b) of the RAI question. Part 2 describes the analysis performed to show why failure of the subject welds is highly unlikely.

Part 3 describes the qualification of a test weld performed to demonstrate that the original installation weld procedure could have been qualified as required by the construction code. Part 4 describes PG&E commitments to inspect for flaws in the subject welds through their service life, including any period of extended operation if authorized, to assure their continued readiness .

Part 1: Safety significance impact and impact on nearby equipment and personnel (a) One safety injection (SI) pump is required to be credited for the intermediate break loss of coolant accident (LOCA) where its parallel Sl pump is assumed to fail (single failure). Failure of the subject socket welds on Sl pump vent and drain connections are not a part of the Diablo Canyon Power Plant (DCPP) design bases calculations.

Should one or more vent and drain weld connections develop a through-wall crack or be completely severed on the operating Sl pump, leakage would develop with severity corresponding to the flaw characteristics. In the worst hypothetical case of complete severances, the safety function of the Sl pump would be lost.

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Enclosure 1 PG&E Letter DCL-15-038 (b) In case of complete severance of one or more vent and drain weld connections on a single Sl pump, the safety function of its parallel Sl pump could potentially be affected if the water level in the room rose to the level of the pump motor casing ventilation openings since they are in the same pump room, separated by a partial dividing wall. There are floor drains in the room which may mitigate the water intrusion.

Any personnel in the room would have adequate time to evacuate the room prior to the flood water level rising to more than a few inches.

However, based on 'the analysis described below in Part 2, the qualification tests detailed below in Part 3, nondestructive examinations (NOEs) conducted on the installed welds as detailed in the relief request, and vibration measurements conducted as detailed in the response to question RAI-EPNB 3.0 below, PG&E has concluded the possibility that one or more vent and drain socket welds could fail (hypothetical scenarios discussed above) is highly unlikely.

Part 2: Summary of SIA Report A summary of the Stress and Fracture Mechanics Evaluation Report (Attachment 3 in Reference 1) prepared by Structural Integrity Associates (SIA) is presented below:

• Flaw growth analysis from outside diameter (OD) to inside diameter (I D) was considered, for postulated OD flaws that could have been missed by inspections. Based on the analysis, the report concluded that growth of OD flaws by fatigue is minimal and flaws do not reach the critical size before the end of the evaluation period.

• Flaw growth analysis from ID to OD was considered, for postulated ID flaws. Based on the analysis, it is concluded that ID flaws will not grow, due to cyclic stress intensity factors below the threshold for fatigue crack growth.

• Worst-case operating loads for any Sl pump weld are used to conservatively bound all welds for the fracture mechanics analysis.

• Worst-case material toughness values for untempered martensitic Type 41 0 stainless steel are conservatively considered in the fracture mechanics analysis.

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Enclosure 1 PG&E Letter DCL-15-038

• Stress corrosion cracking is unlikely to occur, due to the controlled water purity and low temperature of the safety injection system.

• Based on PG&E evaluation of the vibration data, the maximum measured velocity is equal to or less than 0.5 inch per second.

Per the ASME OM3 criteria for assessing vibration in nuclear power plant piping, this is an acceptable level of vibration to prevent vibration-induced crack initiation and growth. In the fracture mechanics analysis, no credit is taken for strongly compressive weld residual stresses near the* 00, which would resist vibration-induced damage.

Part 3: Summary of ATS Report PG&E Applied Technical Services (ATS) Report 420DC-14.20 (Attachment 2 in Reference 1) documents results from a test weld qualification, with the objective of demonstrating the existing Sl Pump attachment welds procedure could have been qualified in accordance with ASME Section IX.

ATS considered the following factors in performing this work:

• The performance of any weldment in Type 41 0 material will be largely influenced by the heat affected zone (HAZ) of base material immediately adjacent to the weld metal. In Type 410 materials, the heat of welding will typically produce untempered martensite within the HAZ. Compared to unwelded Type 41 0 material, the HAZ will have increased hardness, increased yield and tensile strengths, but decreased ductility and notch toughness. These effects become more pronounced with increasing levels of carbon within the alloy of the Type 41 0 material.

Although ASME Section IX does not place restrictions on the carbon content of the qualification coupon, ATS welded a qualification coupon of Type 41 0 material with the highest carbon content which could be readily obtained. ASTM specifications permit Type 410 materials to be produced with up to 0.15 percent carbon, though products often have less. Material with a carbon content of 0.13 percent was used to produce the ATS qualification coupon.

• HAZ mechanical properties will also be influenced by the minimum temperature of the material at which welding is performed, with higher temperatures giving superior results. The Welding 3

Enclosure 1 PG&E Letter DCL-15-038 Procedure Specification (WPS) used to perform the Sl Pump weldments was qualified with a minimum material temperature of 50°F. ASME Section IX rules permit the minimum temperature of a test weld to be up to 100°F above that of the supported production welds. For this reason, welding of the ATS test weldment was performed with a minimum material temperature of 67°F.

• HAZ mechanical properties can also be influenced by the maximum temperature the weldment experiences between deposited passes of weld metal (i.e, "interpass temperature"). A higher interpass temperature will produce superior results in the HAZ of the Type 41 0 material, but an excessively high interpass temperature may degrade properties elsewhere in the weld. The WPS used to perform the Sl Pump weldments permitted a maximum interpass temperature of 350°F.

ASME Section IX rules permit the maximum interpass temperature of a test weld to be as much as 100°F less than that of the supported production welds. For this reason, the ATS test weldment was performed with a maximum interpass temperature of 297°F.

• Postweld heat treatment (PWHT) can be used to improve the mechanical properties in the HAZ. However, since the existing Sl Pump welds had not been given PWHT, no PWHT of the ATS weldment was performed.

• The use of planned weld bead placement in conjunction with controlling welding heat input (also .known as "temperbead welding") can be used to achieve the effects of PWHT in some materials. The ASME Code provides requirements for temperbead welding on low alloy steels, but not for Type 41 0 materials.

Additionally, PG&E is not aware of any experimental data or alternative code requirements for temperbead welding of Type 41 0 materials.

The welding procedure used to install the Sl Pump weldments did not contain any provisions for temperbead welding. Therefore, ATS did not invoke any special controls on bead placement or heat input for the test weldment, instead using only normal welding practices as performed by the welder.

• The existing Sl Pump weldments join % inch Schedule 80 (nominal thickness = 0.154-inch) Type 410 nozzle stub tubes to Type 304 fittings via socket welds.

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Enclosure 1 PG&E Letter DCL-15-038 Although ASME Section IX permits use of a socket configuration for test welds, groove weld configurations allow qualification for a greater range of welding conditions and provide mechanical test specimens which cannot be obtained from a socket weld.

Additionally, Type 410 plate material is more readily available than pipe. For these reasons, ATS performed the test weld using a groove weld configuration.

Face and root bend specimens as well as tensile specimens were removed from the coupon and tested as required by ASME Section IX:

• The face bend and root bend specimens were bent around a mandrel so that a strain of at least 20 percent was achieved. The bent portion of the specimens included both base metals, the weld, and the HAZ in both base metals. The outer surface of the bent specimens was visually inspected and no flaws were seen, which complies with the ASME Section IX criteria, which permits flaws up to 1/8 inch. The 20 percent strain imposed exceeded the strain expected under any design conditions for the Sl Pump welds, and demonstrates an acceptable level of ductility.

Based on these results, it can be concluded that the existing Sl Pump welds will not fail under the strains imposed by the design conditions for these welds.

• Two transverse tensile tests were performed which measured the ultimate tensile strength of both base metals, the weldment, and the HAZ in both base metals. Both specimens failed in the Type 41 0 base metal, with both failing at a stress in excess of the 65 kips per square inch (ksi) minimum required (one specimen failed at 75.5 ksi, the other at 76.0 ksi). The lack of failure in the weldment and HAZ indicates their tensile strengths are in excess of these values.

Based on these results it can be concluded that the existing Sl Pump welds comply with the design requirements for tensile strength.

• Charpy testing was not performed since both the existing Sl Pump welds as well as the ATS test weld are less than the 5/8-inch minimum thickness for which ASME Section Ill imposes testing to assess material toughness. The ASME Section Ill minimum thickness requirement is in recognition that brittle fracture is not a design concern for comparatively thin materials.

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Enclosure 1 PG&E Letter DCL-15-038 Subsequent to the weld demonstration tests described above, PG&E acquired a new Arc-Met alloy analysis device. The new device has a somewhat smaller contact head that was able to obtain measurements on 3 stub tubes on Sl Pump 1-1 and two each on Pumps 1-2 and 2-1.

Full test results are attached to Revision 2 of the relief request. The measurable stub tubes on Pumps 1-2 and 2-1 directly tested carbon content of 0.08 percent or less. For Pump 1-1, the uncorrected results for carbon are summarized here:

51 Pump 1-1 Vent Case Drain Suction Drain Disch Drain Carbon 0.17 Unmeasurable 0.17 0.15 To demonstrate applicability of the weld coupon test results, the Type 410 weld test coupon with mill certified carbon content of 0.13 percent (described above) was also measured using the Arc-Met. The Arc-Met measured a carbon content higher than the mill certified value, as shown below. Using the difference as a correction factor for the measurements on the installed stub tubes indicates the weld coupon is a valid demonstration test for the material properties of the installed equipment.

41055 Welding Test Coupon Ht950163 Mill Cert Arc Met Carbon 0.13 0.163 Part 4: Commitment to revise Surveillance Test Procedures and the lnservice Inspection Program Plan Revision 2 of Relief Request REP-S I incorporates commitments to revise Surveillance Test Procedures (STPs) for quarterly testing of Sl Pumps 1-1, 1-2 and 2-1 to require visual examination of the subject vent and drain connections for evidence of external leakage and to revise the lnservice Inspection (lSI) Program Plan for the fourth and any subsequent lSI intervals to require NDE surface examination (liquid penetrant method) of the Sl pump connection welds where the carbon content of the 41 OSS base metal exceeds 0.08 percent, or is not measurable due to insufficient access for Arc-Met testing. These commitments will provide continued assurance that no flaws exist at these locations.

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Enclosure 1 PG&E Letter DCL-15-038

Reference:

1. PG&E Letter DCL-14-060, "ASME Section Xllnservice Inspection Program Request for Alternative REP-SI: Proposed Alternative to Requirements for Repair/Replacement Activities for Certain Safety Injection Pump Welded Attachments," dated July 21, 2014 (ML14202A613) 7

Enclosure 1 PG&E Letter DCL-15-038 NRC Question RAI-EPNB 2.0:

The industry operating experience has shown that socket welds are susceptible to through-wall cracking.

(a) Please discuss whether any leakage detection systems are available to detect any potential leak from the subject socket welds and whether the operators in the control room would be notified of the leakage.

(b) Please discuss the consequence of a through-wall leak and a complete severance at any of the subject socket welds.

PG&E Response:

Part (a)

Each unit's safety injection pumps (SIPs) are located within a common room --two pumps per room, one room per unit-- on the 85 foot level of the Auxiliary Building. Each train of each Unit's SIPs are physically separated by a concrete partition wall which runs parallel to either SIP shaft's long axis and has open passage ways at each end of the partition. Each SIP is sled mounted atop an equipment pedestal and adjacent to each SIP pedestal is an open floor drain. Each SIP pedestal also has an open equipment drain. The two open floor drains and two open pedestal drains within each Unit's SIP rooms gravity feed directly to the Auxiliary Building sump.

There is no dedicated leakage detection system within the SIP rooms.

However, given a line break in the SIP room during a time when SIPs are supplying cooling water to the reactor core, the operators in the control room would see a reduced SIP flow rate and discharge pressure. If the break is severe enough to challenge the capability of the pumps, the control room could receive alarms on SIP motor temperatures and/or overcurrent trip, and/or increased activity in the Auxiliary Building Ventilation System (ABVS). The control room may also be notified of increasing sump levels.

Additionally, operators walk down the SIP rooms on at least a daily basis during normal rounds. Engineers perform system walkdowns on at least a quarterly basis and also perform Emergency Core Cooling System leakage assessment surveillances (Surveillance Test Procedures M-86 and M-87) and it is required that abnormal system leakage would be reported to the on-shift operations Shift Foreman.

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Enclosure 1 PG&E Letter DCL-15-038 Part (b)

Small leaks resulting from through wall cracks would first manifest as visually detectable buildups of boric acid crystals around the leak path, with leakage pooling locally and eventually making its way to the drains.

More extensive postulated active fluid leaks (e.g., resulting from complete severance of a vent or drain line within the room) would gravity drain to the Auxiliary Building sump (ABS) via the previously described open drains. The ABS level is monitored remotely at the Auxiliary Building Control Board (HMI) and has both Hi and Hi-Hi Level alarms. In addition to their normal rounds in the Auxiliary Building (including SIP rooms),

operators on-watch at the Auxiliary Control Board are required to investigate the cause of the ABS Hi-Hi Level alarms. Additionally, if the postulated break(s) were to occur during a non-accident situation, the Refueling Water Storage Tank (RWST) Low Level Alarm would come in as RWST level approached Technical Specification operational limits.

With non-vital power available, on an ABS Hi-Level alarm, one ABS pump automatically starts pumping down the ABS to the 15,000 gallon Floor Drain Receiver (FOR) Tank. On an ABS Hi-Hi Level alarm both ABS pumps auto start and discharge to the FOR. With non-vital power unavailable (i.e., Loss of Off Site Power), no ABS level indication, no level alarm, and no auto ABS pump starts will occur and the ABS, if in leakage continues, will spill over onto the 54-foot level of the Auxiliary Building.

The 54-foot level can contain approximately 100,000 gallons of water before the level will reach the 58-foot level of the Auxiliary Building challenging the residual heat removal (RHR) pump room sump.

However, as detailed in the response presented above for the previous RAI question RAI-EVIB 1.0, PG&E has concluded the possibility that one or more vent and drain socket welds could fail completely (hypothetical scenarios discussed in RAI-EVIB 1.0. and RAI-EPNB 2.0) is highly unlikely.

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Enclosure 1 PG&E Letter DCL-15-038 NRC Question RAI-EPNB 3.0:

When the safety injection pumps are running; Please discuss whether vibration exists on the drain lines and vent lines. If yes, discuss the potential for the vibration that may cause cracking at the socket welds.

PG&E Response:

To determine if the level of vibration on the vent and drain connections is acceptable, PG&E collected vibration data on all affected vent and drain lines (for all three Sl Pumps: 1-1, 1-2, and 2-1). The vibration data was collected when the pumps were running in "Recirc Mode."

The vibrations during the "Recirc Mode" of operation are expected to be higher when compared to the vibrations during full-flow conditions since the pump's efficiency is about 10 percent during the "Recirc Mode,"

whereas the pump's efficiency is greater than 70 percent during the full-flow conditions and due to its flow characteristic.

Based on PG&E evaluation of the vibration data, the maximum measured velocity is equal to or less than 0.5 inch per second. Per the ASME OM3 criteria for assessing vibration in nuclear power plant piping, this is an acceptable level of vibration to prevent vibration-induced crack initiation and growth.

Also see the response presented above in RAI-EVIB 1.0, Part 2.

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Attachment 1 Enclosure 1 PG&E Letter DCL-15-038 List of Commitments Commitment Number 1 Commitment to revise Surveillance Test Procedures (STPs) to include visual inspection for leakage.

Surveillance test procedures (STPs) for quarterly testing of Safety Injection (SI)

Pumps 1-1 , 1-2, and 2-1 will be revised to require the test performer to visually examine the subject vent and drain connections for evidence of external leakage.

Leakage at these locations would be readily detectable due to accumulation of boric acid crystals at the leak site.

Commitment Number 2 Commitment to include periodic NDE in the lSI Program Plan The lnservice Inspection (lSI) Program Plan for the fourth lSI Interval is being prepared to require nondestructive examination (NDE) surface examination (liquid penetrant method) of the Sl pump vent and drain connection welds where the carbon content of the 41 OSS base metal exceeds 0.08 percent or is not measurable due to insufficient access for Arc-Met testing. The liquid penetrant examinations will be performed on an lSI periodic basis (once every 40 months),

with the interval starting May 7, 2015, for Unit 1 and March 13, 2016, for Unit 2.

Liquid penetrant examinations conducted in December 2014 demonstrated absence of preexisting outside diameter (00) surface flaws in support of the 00 flaw growth analysis. The commitment for ongoing NDE on an lSI periodic basis will provide continued assurance that no flaws exist at these locations. This examination will be included in all future lSI interval Program Plans.

1

Enclosure 2 PG&E Letter DCL-15-038 10 CFR 50.55a Request Number REP-51, Revision 2 Proposed Alternative In Accordance with 10 CFR 50.55a(z)(2)

-Compliance with the specified requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety-Table of Contents

1. ASME Code Component Affected

2. Applicable Code Edition and Addenda

3. Applicable Code Requirement

4. Reason for Request

5. Proposed Alternative and Basis for Use 5.1 Welding Procedure Qualification Tests 5.2 Stress and Fracture Mechanics Evaluation 5.3 Nondestructive Examinations 5.4 Review of Sl Pumps Operating History 5.5 Hardship 5.6 Commitments for Visual Examination and Nondestructive Examination

5. 7 Conclusion

6. Duration of Proposed Alternative

7. References : Comprehensive Arc-Met Testing Results 1

Enclosure 2 PG&E Letter DCL-15-038 10 CFR 50.55a Request Number REP-51, Revision 2 Proposed Alternative In Accordance with 10 CFR 50.55a(z)(2)

-Compliance with the specified requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety-

1. ASME Code Components Affected Diablo Canyon Power Plant (DCPP) Unit 1, ASME Code Class 2, Safety Injection (SI) Pump 1-1 nominal pipe size (NPS)% inch vent and drain connection socket weld attachments (four attachment welds) and Sl Pump 1-2 NPS 3/4 inch drain connection socket weld attachments (two attachment welds); and DCPP Unit 2, ASME Code Class 2, Sl Pump 2-1 NPS % inch drain connection socket weld attachments (two attachment welds). (Note: The remaining vent and drain attachment welds on each Sl Pump 1-2 and 2-1 (two welds per pump) were fabricated in conformance with applicable requirements and are no longer included in this relief request. DCPP Unit 2 Sl Pump 2-2 vent and drain connections were manufactured differently and are not affected).

2. Applicable Code Edition and Addenda ASME Section XI, 2001 Edition through 2003 Addenda

3. Applicable Code Requirement IWA-4000, "Repair/Replacement Activities," including IWA-4130, "Alternative Requirements," and IWA-4131, "Small Items," as corrective action for the four affected Code Class 2, NPS % inch socket welds on Sl Pump 1-1 and two affected welds each on Sl Pumps 1-2 and 2-1.

4. Reason for Request Relief is requested from implementing the Section XI repair/replacement rules for nonconforming % inch nominal diameter vent valve and drain pipe fitting attachment socket welds. These welds connect to four integrally attached stub piping nipples on Sl Pump 1-1 and two nipples each on Sl Pumps 1-2 and 2-1. (Note: larger diameter pipe connections to these pumps were supplied with integral flanged connections and are not affected).

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Enclosure 2 PG&E Letter DCL-15-038 The Unit 1 Sl Pumps 1-1 and 1-2 and Unit 2 Sl Pump 2-1 are size 2 %,

Type JTCH, manufactured by Pacific Pumps. The pump casings are fabricated from martensitic stainless steel and were each supplied with four integrally attached % inch nominal diameter Type 410 martensitic stainless steel (ASME material type P-6) pipe nipple stubs. One integral vent stub nipple and three integral drain stub nipples were supplied with each pump. The pump casings including the pipe nipples and their attachment welds to the pump casings were heat treated during pump manufacture and supplied as an integral pump assembly.

The Unit 1 Sl pumps and connected piping were installed in 1974 and the Unit 2 Sl Pump 2-1 and connected piping was installed in 1975 by the original plant construction piping and equipment installation contractor.

During original installation of the pump assemblies in the plant, Type 316 austenitic stainless steel (ASME material Type P-8) isolation valves were welded to the integral vent stub nipple connections, and Type 304 austenitic stainless steel (ASME material Type P-8) pipe fittings (elbows, tees, or a coupling) were welded to each of the integral drain stub nipple connections supplied with each pump. The valve- or fitting-to-stub nipple attachment welds were made using the pipe and equipment installation contractor's welding procedure specification number 149 (see of Reference 1) using Type 309 stainless steel filler metal.

Procedure 149 was qualified for welding carbon steel (ASME material Type P-1) to austenitic stainless steel (ASME material Type P-8).

Procedure 149 was not qualified for welding martensitic stainless steel (ASME material Type P-6) to austenitic stainless steel (ASME material Type P-8). The procedure would be satisfactory for the application with the exception that it does not contain provision for post-weld heat treatment that would potentially be required by a Type P-6 to P-8 procedure. Heat treatment would be required for welding Type P-6 to P-8 material when the carbon content of the Type P-6 base metal exceeds 0.08 percent. The discrepancy in welding procedure qualification was discovered in December 2013 during material verification as part of the planning process for anticipated replacement of the Pump 1-1 Vent Valve due to boric acid leakage from the valve packing.

Subsequent to the attempted Arc-Met testing described in Section 5.1, a new Arc-Met machine having a somewhat smaller contact head was purchased. The new machine enabled measurement of several of the stub nozzles that were not accessible to the original machine. The carbon content of each stub nipple was measured using the new Arc-Met machine when sufficient access permitted. The complete results are attached in Table 1 (Attachment 1) and summarized here:

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Enclosure 2 PG&E Letter DCL-15-038 0

/o Carbon Vent Case Drain Suction Drain Discharge Drain Pump 1-1 0.17 Inaccessible 0.17 0.15 Pump 1-2 0.05 Inaccessible Inaccessible 0.02 Pump 2-1 0.04 Inaccessible 0.08 Inaccessible The vent and discharge drain on Pump 1-2 and the vent and suction drain on Pump 2-1 are 0.08 percent carbon or less; therefore they do not require post-weld heat treatment per the construction code and are not included in this relief request Revision 2. The measurements for Pump 1-1 showed abnormally high carbon content. To check the accuracy of these results, the weld test coupon material having certified mill test report (CMTR) carbon content of 0.13 percent was checked using the Arc-Met, with a resulting measurement of 0.163 percent. Using the difference between the CMTR and the measured value as a correction factor, the results are consistent with the material specification and correspond with the carbon content of the weld test coupon.

ASME Section XI would require use of IWA-4000 repair/replacement rules for correction of the nonconforming %-inch nominal diameter socket welds on each subject pump. The four welds on Pump 1-1 either exceed 0.08 percent carbon or are inaccessible. Two welds each on Pumps 1-2 and 2-1 are inaccessible for test.

5. Proposed Alternative and Basis for Use PG&E proposes to accept the existing Sl Pumps 1-1, 1-2, and 2-1 vent and drain attachment socket welds as-is.

To confirm acceptability of the existing Sl pump's vent and drain socket welds, PG&E has:

• confirmed by Arc-Met testing that the carbon content of the vent stub and one drain stub each on Sl Pumps 1-2 and 2-1 have carbon content equal to or less than 0.08 percent, thus meeting the applicable requirement for welding Type 41 0 stainless steel to austenitic stainless steel without post-weld heat treatment. The remaining two stubs on these two pumps are inaccessible for testing. The case drain on Pump 1-1 is also inaccessible.

• conducted welding procedure qualification tests with representative Type 41 0 stainless steel and Type 304 stainless steel base materials using Type 309 filler metal as per the original Welding Procedure Specification (WPS) 149 parameters without post-weld heat treatment (see Attachment 2 of Reference 1);

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Enclosure 2 PG&E Letter DCL-15-038

• performed a Stress and Fracture Mechanics Evaluation of Type 410 Stainless Steel Weldments in Sl Pumps at DCPP (see Attachment 3 of Reference 1);

• performed NDE examinations of the subject welds to determine and verify current conditions; and

• performed a review of the Sl pumps operating histories including pressure test records.

Each of these actions are discussed below and detailed in the attachments of Reference 1. Additionally, to assure the current acceptable baseline conditions are maintained for the subject welds going forward, PG&E is committing to visually examine the subject welds for leakage during scheduled quarterly surveillance tests and to perform surface NDE (liquid penetrant examination) on an inservice inspection (lSI) periodic basis for the remaining service life of the pumps, including any authorized license extension period.

5.1 Welding Procedure Qualification Tests Welding Procedure Qualification Test Report is presented in Attachment 2 of Reference 1. For the weld qualification tests, Arc-Met testing to determine carbon content of the existing Sl pumps Type 41 0 stainless steel pipe nipples was attempted but initially proved unsuccessful due to the small pipe size, short lengths of the drain nipples and adverse component configurations. As a result, Type 410 stainless steel material with the highest carbon content readily available (0.13 percent) was used for the qualification testing. To qualify the procedure, 3/8 inch thick Type 41 0 stainless steel plate was welded to 3/8 inch thick Type 304 stainless steel plate using a combination of gas tungsten arc welding (GTAW) at the root with shielded metal arc welding (SMAW) for the cover passes. Ambient condition preheat of 66.5°F was used with maximum interpass temperature of 297°F recorded. No use of planned weld bead placement in conjunction with controlling heat input (also known as "temperbead welding") was performed. No post weld heat treatment was used.

The final weld was sectioned to provide two tensile and four bend test specimens which were tested by an independent laboratory. Two of the bend specimens were subjected to root bending 180 degrees and two were subjected to face bending 180 degrees over rollers with diameter of 4 times the bend specimen thickness, with the weld and heat-affected zones centered within the convex length of bent samples per ASME Section IX, Table QW-451.1 and QW-160, 2013 Edition. The samples were subsequently examined for cracks and other defects and all were found acceptable.

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Enclosure 2 PG&E Letter OCL-15-038 The two tensile test specimens were tested in accordance with ASME Section IX, Table QW-451.1 and QW-150, 2013 Edition, with required ultimate tensile strength of 65 kips per square inch (ksi). Actual ultimate tensile strengths of 75.5 ksi and 76.0 ksi respectively were recorded, with the breaks occurring in the Type 41 0 stainless steel parent metal in both instances.

Subsequently, a new Arc-Met device was acquired. The new Arc-Met device has a somewhat smaller contact head and was able to measure several of the stub tubes as previously described. The Arc-Met results confirm that where measurement is possible, the weld tests described above are representative of the installed materials.

5.2 Stress and Fracture Mechanics Evaluation Stress and Fracture Mechanics Evaluation Report prepared by Structural Integrity Associates (SIA) is presented in Attachment 3 of Reference 1.

SIA's evaluation of the %-inch Type 41 0 stainless steel nipples welded to Type 316 valves or Type 304 fittings without post weld heat treatment on the OCPP Sl Pump vent and drain lines consisted of stress analysis, evaluation of allowable flaw size under maximum loading, and evaluation of crack propagation of postulated flaws under cyclic fatigue loading. A fracture mechanics approach analogous to the methods of ASME Code Section XI, supplemented with procedures from American Petroleum Institute Standard API-579, was used because the ASME Section XI methods do not address Type 410 martensitic stainless steels, evaluation of (postulated) flaws on piping outside diameter (00) surfaces, or evaluation of flaws in piping of diameter 4 inches or less.

The postulated flaw extends from the socket weld toe on the Type 41 0 stainless steel nipple, which is the region where cyclic stresses are the largest, and grows from the 00 toward the inside diameter (10).

Additionally, a postulated flaw originating at the 10 was evaluated due to tensile stresses as a result of residual stress from welding.

The depths of 00 and 10 flaws located along the largest cyclic stress path that would cause crack instability under maximum operating loads and pressure, including seismic/abnormal loads and applicable structural factors, were evaluated. The allowable flaw depth for an 00 flaw was determined to be 0.110 inch, approximately 71.6 percent of the wall thickness of 0.154 inch. The allowable flaw depth for an 10 flaw was found to exceed 80 percent of the wall thickness.

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Enclosure 2 PG&E Letter DCL-15-038 For cyclic loading, postulated ID flaws are not predicted to grow as all cyclic stress intensity factors are below the fatigue threshold.

For postulated OD crack analysis, 7000 thermal transient cycles, 400 design earthquake cycles, and 20 Hosgri earthquake cycles were considered. For the postulated OD crack to grow by fatigue under cyclic operating loads and pressure to the allowable flaw size in the evaluated number of cycles, an initial crack of at least 0.104 inch depth is required.

This depth corresponds to a surface length of 0.832 inch for a crack aspect ratio of 4.

For nondestructive test minimum length detection limits of 1/16 inch (such as for liquid penetrant examinations), fatigue crack growth will not occur for a postulated OD flaw whose surface length is equal to the detection limit, even for load cycles associated with the Hosgri earthquake.

For a postulated 10 percent through-wall OD flaw, no growth is predicted except for the 20 cycles assumed for the Hosgri event. For that case, the associated crack extension is 8.3 x 1o-6 inch.

For a postulated OD crack 0.026 inch deep Oust exceeding the fatigue crack growth threshold), the amount of crack extension under the evaluated cyclic loading is 0.0015 inch.

The evaluations of the postulated OD and ID flaws show that crack growth under anticipated cyclic loading is minimal.

5.3 Nondestructive Examinations During the operating history of the plant, the subject welds have been examined by qualified VT-2 visual examiners every 40 months during scheduled ASME Section XI system pressure tests. No leakage from any of the welds has ever been identified.

Liquid penetrant examinations of all vent and drain connection welds on the subject Sl pumps were performed between December 18 and 20, 2013, with specific attention focused for crack-like indications. No linear or crack-like indications were detected.

5.4 Review of Sl Pumps Operating History The cumulative number of starts is a measure of the cyclic loading experienced by the pumps, as analyzed in the stress and fracture mechanics evaluation. The Sl pumps were each started several times 7

Enclosure 2 PG&E Letter DCL-15-038 during testing prior to plant operation. During plant operation, the pumps normally function in a stand-by capacity and are periodically started for pump readiness testing and system pressurizations for leak testing, as well as a small number of starts in support of the Sl function.

Preoperational starts are an estimate of the number of Sl pump starts during preoperational startup testing activities and during three Plant Hot Functional Testing programs. Each pump is estimated to have had 25 preoperational starts.

The total number of operational starts for Sl Pumps 1-1, 1-2, and 2-1 through the end of 2013 was estimated using the operating data of each of these pumps to establish an annual average. This average, 11 starts per year for each pump, was extrapolated back to the commencement of plant operation.

Total preoperational and operational start estimates were then added together. The resulting estimated number of starts for each Sl pump during the life of the plant was multiplied by 2 as a conservative measure allowing for a higher number of starts per year at beginning of plant life plus any pressurizations of the Sl piping by means other than a pump start, such as hydro testing.

The calculation of total starts for each pump is thus as follows: [Number of preoperational starts plus (Average number of starts per year multiplied by number of years of plant operation)] multiplied by 2.

Total starts for Sl Pumps 1-1 and 1-2: [25 starts+ (11 starts/year X 29 years)] X 2 = 688 starts Total starts for Sl Pump 2-1: [25 starts+ (11 starts/year X 28 years)] X 2

= 666 starts.

The total number of starts to date (approximately half of plant life assuming a 20 year license renewal extension) for each of the subject Sl pumps is conservatively estimated to be less than 700 starts.

Conservatively assuming an additional 700 starts during the second half of plant life (including the assumed 20 year license extension period), the total number of Sl pump starts during all of plant lifetime is estimated to be less than 1400 starts. This is well under the 7000 thermal transient cycles assumed in the fatigue crack growth analysis.

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Enclosure 2 PG&E Letter DCL-15-038 5.5 Hardship The existing vent stub nipple to vent valve and drain stub nipples to drain pipe fittings socket welds were made in accordance with the original construction contractor's WPS 149 which did not provide for post weld heat treatment. The stub nipples are short, typically less than 4 inches in length, with the casing drain nipple being less than one inch long.

Photographs of each attachment to Pump 1-1, which are typical of all of the pumps, are included for reference in Attachment 1 of Reference 2.

Attempting to perform localized heat treatment would jeopardize the factory heat treatment of the entire pump casing. Heat treatment of the entire pump casing to include these small welds cannot be performed in situ under the same controlled conditions available during factory fabrication. Either means of attempting heat treatment could result in warping or damage to the pump casing. These factors constitute a hardship for compliance with the specified requirements.

5.6 Commitments for Visual Examination and NDE To provide continued assurance of the integrity of the affected Sl pump welds, the following tests and examinations will be conducted:

5.6.1 Commitment to revise Surveillance Test Procedures (STPs) to include visual inspection for leakage.

STPs for quarterly testing of Sl Pumps 1-1, 1-2, and 2-1 will be revised to require the test performer to visually examine the subject vent and drain connections for evidence of external leakage during all future tests. Leakage at these locations would be readily detectable due to accumulation of boric acid crystals at the leak site.

5.6.2 Commitment to include periodic NDE in the lSI Program Plan The lSI Program Plan for the fourth lSI Interval is being prepared to require NDE surface examination (liquid penetrant method) of the Sl pump vent and drain connection welds where the carbon content of the 41 OSS base metal exceeds 0.08 percent or is not measurable due to insufficient access for Arc-Met testing. The liquid penetrant examinations will be performed on an lSI periodic basis (once every 40 months), with the interval starting May 7, 2015, for Unit 1 and March 13, 2016, for Unit 2. Liquid penetrant examinations conducted in December 2014 demonstrated absence of preexisting OD surface flaws in support of the OD flaw growth analysis. The commitment for ongoing NDE on an lSI periodic basis will provide continued assurance 9

Enclosure 2 PG&E Letter DCL-15-038 that no flaws exist at these locations. This examination will be included in all future lSI interval Program Plans.

5.7 Conclusion As discussed above and demonstrated and documented in Attachments 2 and 3 of Reference 1, attempting to heat treat the nipple to socket welds would require either localized heating or heating the entire pump casing.

Either evolution could not be performed in situ under the same controls as available during original factory fabrication of the pumps and could thus result in warping or other damage to the pumps. The existing Sl pump's vent and drain socket welds were fabricated using a procedure satisfactory in all respects other than post weld heat treatment. This procedure has been demonstrated to produce the required mechanical properties of a post weld heat treated procedure. Accordingly, compliance with the specified requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety in accordance with 10 CFR 50.55a(z)(2); thus the existing weldments may be determined acceptable as-is for continued service.

6. Duration of Proposed Alternative The proposed alternative will apply for the remaining service life of Sl Pumps 1-1, 1-2, and 2-1, including the duration of the current operating licenses plus a contemplated license extension period of 20 years if authorized.

7. References

1. PG&E Letter DCL-14-060, "ASME Section Xllnservice Inspection Program Request for Alternative REP-SI: Proposed Alternative to Requirements for Repair/Replacement Activities for Certain Safety Injection Pump Welded Attachments," dated July 21, 2014 (ML14202A613)

2. PG&E Letter DCL-15-021, "Response to NRC Request for Additional Information Regarding Relief Request REP-SI," dated February 5, 2015 (ML15036A606) 10

Attachment 1 Enclosure 2 PG&E Letter DCL-15-038 Comprehensive Arc-Met Testing Results (February 27, 2015)

Sl Pump 1-1 Element Vent Case Drain Suction Drain Disch Drain Carbon 0.17 Unmeasurable 0.17 0.15 Manganese 0.52 Unmeasurable 0.54 0.51 Silicon 0.37 Unmeasurable 0.3 0.37 Chromium 12.25 Unmeasurable 11.99 12.01 Nickel 0.36 Unmeasurable .0.36 0.35 Titanium 0.006 Unmeasurable 0.006 0.006 Aluminum <0.003 Unmeasurable 0.006 <0.003 Sl Pump 1-2 Element Vent Case Drain Suction Drain Disch Drain Carbon 0.05 Unmeasurable Unmeasurable 0.02 Manganese 0.67 Unmeasurable Unmeasurable 0.66 Silicon 0.28 Unmeasurable Unmeasurable 0.3 Chromium 12.09 Unmeasurable Unmeasurable 12.15 Nickel 0.09 Unmeasurable Unmeasurable 0.09 Titanium 0.005 Unmeasurable Unmeasurable 0.005 Aluminum 0.004 Unmeasurable Unmeasurable 0.004 Sl Pump 2-1 Element Vent Case Drain Suction Drain Disch Drain Carbon 0.04 Unmeasurable 0.08 Unmeasurable Manganese 0.66 Unmeasurable 0.65 Unmeasurable Silicon 0.29 Unmeasurable 0.33 Unmeasurable Chromium 12.11 Unmeasurable 12.07 Unmeasurable Nickel 0.09 Unmeasurable 0.09 Unmeasurable Titanium 0.005 Unmeasurable 0.012 Unmeasurable Aluminum 0.005 Unmeasurable 0.026 Unmeasurable No measurement was possible on the case drains, the 1-2 Suction Drain or 2-1 Discharge Drain.

410SS Welding Test Coupon Ht950163 Mill Cert Arc Met Carbon 0.13 0.163 11