DCL-04-028, License Amendment Request 04-01, Revised Steam Generator Voltage-based Repair Criteria Probability of Detection Method

License Amendment Request 04-01, Revised Steam Generator Voltage-based Repair Criteria Probability of Detection Method

ML040840449
Person / Time
Site:	Diablo Canyon
Issue date:	03/18/2004
From:	Oatley D Pacific Gas & Electric Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
DCL-04-028
Download: ML040840449 (31)

Text

-WI PacificGas and Electric Company David H.Oatley Diablo Canyon Power Plant Vice President and PO. Box 56 General Manager Avila Beach, CA 93424 March 18, 2004 Fax 805.545.4234 PG&E Letter DCL-04-028 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555-0001 Docket No. 50-275, OL-DPR-80 Docket No. 50-323, OL-DPR-82 Diablo Canyon Units 1 and 2 License Amendment Request 04-01 Revised Steam Generator Voltage-based Repair Criteria Probability of Detection Method for DCPP Units 1 and 2 In accordance with 10 CFR 50.90, enclosed is an application for amendment to Facility Operating License Nos. DPR-80 and DPR-82 for Diablo Canyon Power Plant (DCPP) Units I and 2. The enclosed license amendment request (LAR) requests NRC approval to update the DCPP Final Safety Analysis Report Update (FSARU) to use a revised steam generator (SG) voltage-based repair criteria probability of detection (POD) method using plant specific SG tube inspection results. The proposed POD method is referred to as the probability of prior cycle detection (POPCD) method. The POPCD method is requested to be used on a permanent basis for all remaining cycles for DCPP Units 1 and 2 until SG replacement, starting with DCPP Unit 1 Cycle 13 and DCPP Unit 2 Cycle 13.

Technical Specification (TS) 5.5.9, 'Steam Generator (SG) Tube Surveillance Program," and TS 5.6.10, uSteam Generator (SG) Tube Inspection Report," are based on Generic Letter (GL) 95-05, "Voltage-Based Repair Criteria for Westinghouse Steam Generator Tubes Affected by Outside Diameter Stress Corrosion Cracking," dated August 3,1995, which requires the application of a POD of 0.6 to all previous bobbin indications for the determination of the beginning of cycle (BOC) indication voltage distribution for operational assessment. Therefore, the use of the POPCD method to determine the BOC voltage distribution is an exception to GL 95-05 and requires prior NRC review and approval.

The use of a constant POD of 0.6 for determination of the indication voltage distribution for the BOC is nonconservative for indications below about 0.5 volts and excessively conservative for indications above 1 volt. The POPCD method to determine POD provides a more realistic POD that is a function of voltage.

Application of the POPCD method reduces preventive plugging of SG tubes that would otherwise be needed to maintain the conditional probability of burst (POB) less than the TS 5.6.10.d.5 reporting limit of Ixl1o- 2 for the duration of the operating A member of the STARS (Strategic Teaming and Resource Sharing) Alliance Callaway

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Document Control Desk PG&E Letter DCL-04-028 March 18, 2004 Page 2 cycles. Reduction of preventive plugging of SG tubes also maintains reactor coolant system flow margin and reduces personnel dose during refueling outages.

The POPCD method was previously approved in the NRC Amendment No. 164 to Facility Operating License No. DPR-82 in a letter to PG&E dated October 21, 2003, for use in DCPP Unit 2 Cycle 12. The POPCD method uses only data from DCPP Units 1 and 2 SG tube inspections. The POPCD method in this application is identical to the method approved by the NRC in Amendment No. 164.

EPRI is currently developing an outlier growth method for application to outside diameter stress corrosion cracking (ODSCC) alternate repair criteria (ARC) coincident with the use of the POPCD method. Upon completion of the method development, expected by April 2004, the outlier growth methodology will be submitted to the NRC. PG&E will then provide the NRC with revised end of cycle (EOC) 12 projections and EOC 13 projections using the outlier growth method.

Upon NRC approval to use the POPCD method for ODSCC ARC applications for DCPP Units 1 and 2, PG&E will adopt the outlier growth method for application to ODSCC ARC coincident with the use of the POPCD method. contains a description of the proposed change, the supporting technical analyses, the no significant hazards consideration determination, and figures and tables supporting the technical analyses. Enclosure 2 contains the marked-up FSARU pages for information only.

There are no TS changes required to use the POPCD method to determine the BOC voltage distribution.

PG&E has determined that this LAR does not involve a significant hazard consideration as determined per 10 CFR 50.92. Pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental assessment needs to be prepared in connection with the issuance of this amendment.

The change in this LAR is not required to address an immediate safety concern.

PG&E requests approval of this LAR by October 1, 2004, to support use of the POPCD method in the DCPP Unit 1 Cycle 13 and DCPP Unit 2 Cycle 13 operational assessments. PG&E requests the license amendments be made effective upon NRC issuance, to be implemented by incorporation into the FSARU within 30 days of issuance.

If you have any questions or require additional information, please contact Stan Ketelsen at 805-545-4720.

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Document Control Desk PG&E Letter DCL-04-028 March 18, 2004 Page 3 Sincerely, 9iV °161 David H. Oatley Vice President and General Manager - Diablo Canyon kjse/4328 Enclosures cc: Edgar Bailey, DHS Bruce S. Mallett David L. Prouix Diablo Distribution cc/enc: Girija S. Shukla A member of the STARS (Strategic Teaming and Resource Sharing) Alliance Callaway

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PG&E Letter DCL-04-028 UNITED STATES OF AMERICA NUCLEAR REGULATORY COMMISSION

) Docket No. 50-275 In the Matter of ) Facility Operating License PACIFIC GAS AND ELECTRIC COMPANY) No. DPR-80

)

Diablo Canyon Power Plant Docket No. 50-323 Unit 1 and 2 ) Facility Operating License No. DPR-82 AFFIDAVIT David H. Oatley, of lawful age, first being duly sworn upon oath says that he is Vice President and General Manager - Diablo Canyon of Pacific Gas and Electric Company; that he has executed license amendment request 04-01 on behalf of said company with full power and authority to do so; that he is familiar with the content thereof; and that the facts stated therein are true and correct to the best of his knowledge, information, and belief.

9'Vl David H. Oatley

°ov-Vice President and General Manager - Diablo Canyon Subscribed and sworn to before me this 18th day of March 2004.

.~- _6 BREN --

P?-* Cow&ng 14284 Notary Public a jw Pub Cao k- t County of San Luis Obispo .m bObey Le CM

.% ~w.Ewd1 State of California - - -

Enclosure 1 PG&E Letter DCL-04-028 EVALUATION

1.0 DESCRIPTION

This letter is a request to amend Operating Licenses DPR-80 and DPR-82 for Units 1 and 2 of the Diablo Canyon Power Plant (DCPP), respectively.

The proposed change would revise the operating licenses to allow the update of the DCPP Final Safety Analysis Report Update (FSARU) to use a revised steam generator (SG) voltage-based repair criteria probability of detection (POD) method using plant specific SG tube inspection results. The proposed POD method is referred to as the probability of prior cycle detection (POPCD) method.

The POPCD method is to be used on a permanent basis for all remaining cycles for DCPP Units 1 and 2 until SG replacement, starting with DCPP Unit 1 Cycle 13 and DCPP Unit 2 Cycle 13.

Technical Specification (TS) 5.5.9, Steam Generator (SG) Tube Surveillance Program," and TS 5.6.10, "Steam Generator (SG) Tube Inspection Report," are based on Generic Letter (GL) 95-05, "Voltage-Based Repair Criteria for Westinghouse Steam Generator Tubes Affected by Outside Diameter Stress Corrosion Cracking," dated August 3, 1995, which requires the application of a POD of 0.6 to all previous bobbin indications for the determination of the beginning of cycle (BOC) indication voltage distribution for operational assessment. The use of the POPCD method to determine the BOC voltage distribution is an exception to GL 95-05 and requires prior NRC review and approval.

The NRC approved a DCPP-specific POPCD method in the NRC Amendment No. 164 to Facility Operating License No. DPR-82 in a letter to PG&E dated October 21, 2003, for use in DCPP Unit 2 Cycle 12. The POPCD method in this application is identical to the method approved by the NRC in Amendment No. 164. Upon NRC approval to use the POPCD method for outside diameter stress corrosion cracking (ODSCC) alternate repair criteria (ARC) applications for DCPP Units 1 and 2, PG&E will adopt the outlier growth method for application to ODSCC ARC coincident with the use of the POPCD method.

2.0 PROPOSED CHANGE

The requested change would allow use of the POPCD method to determine the BOC voltage distribution for the SG operational assessment. This exception to GL 95-05 does not require a change to the TS since Section 5.5.9, 'Steam Generator (SG) Tube Surveillance Program," and Section 5.6.10, "Steam Generator (SG) Tube Inspection Report," do not specify the bobbin POD to be used or the bobbin indications which are to be used for determination of the BOC indication voltage distribution for the operational assessment.

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Enclosure 1 PG&E Letter DCL-04-028 The proposed FSARU changes are provided for information only in Enclosure 2.

3.0 BACKGROUND

3.1 SG Voltage-based Repair Criteria The SG tubes constitute more than half of the reactor coolant pressure boundary (RCPB) area. Design of the RCPB for structural and leakage integrity is a requirement under Title 10 of the Code of Federal Regulations, Part 50 (10 CFR 50), Appendix A. Specific requirements governing the maintenance and inspection of SG tube integrity are in the DCPP TS, Section Xl of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code, and Regulatory Guide 1.83. DCPP also implements the requirements of NEI 97-06. These include requirements for periodic inservice inspection of the tubing, flaw acceptance criteria (i.e., repair limits for plugging), and primary-to-secondary leakage limits. These requirements, coupled with the broad scope of plant operational and maintenance programs, have formed the basis for assuring adequate SG tube integrity.

SG tube plugging limits are specified in the DCPP TS. The current DCPP TS require that flawed tubes be removed from service by plugging if the depths of the flaws are greater than or equal to 40 percent through-wall, unless the degradation is subject to voltage-based ODSCC repair criteria, W* repair criteria, or primary water stress corrosion cracking within dented tube support plate (TSP) repair criteria. The TS 5.5.9 repair limits ensure that tubes accepted for continued service will retain adequate structural and leakage integrity during normal operating, transient, and postulated accident conditions, consistent with General Design Criteria 14, 15, 30, 31, and 32 of 10 CFR 50, Appendix A. Structural integrity refers to maintaining adequate margins against gross failure, rupture, and collapse of the SG tubing. Leakage integrity refers to limiting primary-to-secondary leakage to within acceptable limits.

The generic criteria for voltage-based limits for ODSCC are contained in GL 95-05. These criteria rely on empirically derived correlations between a nondestructive inspection parameter, the bobbin coil voltage, and tube burst pressure and leak rate. The GL guidance ensures structural and leakage integrity continue to be maintained at acceptable levels consistent with the requirements of 10 CFR 50 and the guideline values in 10 CFR 100 through augmented SG tube inspections and more restrictive operational leakage limits.

GL 95-05 focuses on maintaining tube structural integrity during the full range of normal, transient, and postulated accident conditions with 2

Enclosure 1 PG&E Letter DCL-04-028 adequate allowance for eddy current test uncertainty and flaw growth projected to occur during the next operating cycle. In order to ensure the structural and leakage integrity of the tube until the next scheduled inspection, GL 95-05 specifies a methodology to determine the conditional burst probability and the total primary-to-secondary leak rate from an affected SG during a postulated main steam line break (MSLB) event.

The methodology in WCAP-14277, Revision 1, 'SLB Leak Rate and Tube Burst Probability Analysis Methods for ODSCC at TSP Intersections,"

dated December 1996, is used to implement the GL 95-05 structural integrity methodology.

A probabilistic analysis to quantify the potential for SG tube ruptures given a MSLB event is performed per WCAP-14277, Revision 1, and compared to a reporting threshold value of 1x10-2 per cycle as required by GL 95-05.

This threshold value provides assurance that the probability of burst (POB) is acceptable considering the assumptions of the calculation and the results of the staffs generic risk assessment for SGs contained in NUREG-0844, "NRC Integrated Program for the Resolution of Unresolved Safety Issues A-3, A-4, and A-5 Regarding Steam Generator Tube Integrity." Failure to meet this threshold value indicates ODSCC confined to within the thickness of the TSP could contribute a significant fraction to the overall conditional probability of tube rupture from all forms of degradation assumed and evaluated as acceptable in NUREG-0844.

The calculation of conditional burst probability is, in part, a function of the POD and the resulting indication voltage distribution at BOC. The indication voltage distribution at BOC is based on consideration of all previous bobbin indications that were detected at the BOC, including those that were plugged. The POB threshold value of 1x1 0-2 per cycle is contained in the DCPP Unit 1 and 2 TS 5.6.10.d.5 NRC reporting limit, which requires that PG&E notify the NRC and provide an assessment of safety significance, prior to returning the SGs to service, if the calculated conditional POB based on the projected end of cycle (EOC) voltage distribution exceeds 1x1- 2.

The voltage-based ODSCC repair criteria are briefly described in FSARU section 5.5.2.5.4,"Voltage-Based Alternate Repair Criteria." The use of voltage-based ARC for ODSCC indications at SG TSP intersections was approved by the NRC in Amendment Nos. 124 and 122 to Facility Operating License Nos. DPR-80 and DPR-82, respectively, for DCPP Units 1 and 2 in a letter to PG&E dated March 12,1998. PG&E requested the use of the voltage-based ARC for ODSCC at SG TSP intersections in PG&E letter DCL-97-034, "License Amendment Request 97-03, Voltage-Based Altemate Steam Generator Tube Repair Limit for Outside Diameter Stress Corrosion Cracking at Tube Support Plate Intersections,"

dated February 26, 1997. In letter DCL-97-034, as an alternative to using 3

Enclosure I PG&E Letter DCL-04-028 a very conservative constant POD value of 0.6, PG&E requested the use of a revised POD method. This revised POD is a more realistic POD that is a function of indication voltage and is referred to as the POPCD method. Section 3.1.3 of the NRC safety evaluation for License Amendment Nos. 124 and 122 for DCPP Units 1 and 2 respectively, addressed the structural and leakage integrity assessments related to the ARC and stated that "PG&E will be permitted to use a revised POD, in lieu of a constant value of 0.6, if and when a revised POD is approved by the NRC. Until that occurs, PG&E will have to use a constant value of 0.6."

Based on the requirements of License Amendment Nos. 124 and 122, the use of a POD other than a POD of 0.6 in ODSCC ARC structural and leakage assessments requires prior NRC review and approval.

3.2. POPCD Method PG&E requested application of a plant-specific POPCD method for Unit 2 Cycle 12 in PG&E letter DCL-03-078, uLicense Amendment Request 03-10, Revised Steam Generator Voltage-based Repair Criteria Probability of Detection Method for Diablo Canyon Unit 2 Cycle 12," dated June 26, 2003, as supplemented by PG&E letters dated September 3, 2003 (DCL-03-109) and September 30, 2003 (DCL-03-123). The plant-specific POPCD method included all applicable data from DCPP Units 1 and 2. The NRC approved application of the DCPP-specific POPCD method for DCPP Unit 2 Cycle 12 by Amendment No. 164 to Facility Operating License No. DPR-82 in a letter to PG&E dated October 21, 2003.

The POPCD method requested in letter DCL-03-078 was based, in part, on the POPCD method described in EPRI Topical Report NP 7480-L, Addendum 5, "Steam Generator Tubing Outside Diameter Stress Corrosion Cracking at Tube Support Plates Database for Alternate Repair Limits, Update 2002," dated January 2003, transmitted to the NRC in Nuclear Energy Institute letter, uSteam Generator Degradation Specific Management Database, Addendum 5," dated February 13, 2003.

However, in response to NRC questions, PG&E letters DCL-03-078, DCL-03-109, and DCL-03-123 modified and updated specific details related to classification of indications, voltage bin width, regression analysis, and reporting requirements.

3.3. Purpose for Proposed Amendments The use of a constant POD of 0.6 for determination of the indication voltage distribution for the BOC is nonconservative for indications below about 0.5 volts and excessively conservative for indications above I volt.

The POPCD method to determine POD provides a more realistic POD that is a function of voltage. Application of the POPCD method reduces 4

Enclosure I PG&E Letter DCL-04-028 preventive plugging of SG tubes which maintains reactor coolant system flow margin and reduces personnel dose during refueling outages.

4.0. TECHNICAL ANALYSIS Sections 4.1, 4.2, and 4.3 describe the proposed POPCD method for this LAR and addresses three technical aspects: POPCD method, growth rate considerations, and prior cycle benchmarking of POPCD.

4.1 POPCD Method The POPCD method discussed in Section 4.1 is identical to the method previously approved by the NRC for use in DCPP Unit 2 Cycle 12 by Amendment No. 164 to Facility Operating License No. DPR-82 in a letter to PG&E dated October 21, 2003.

4.1.1 POPCD Definition POPCD is calculated as the ratio of indications reported at the prior inspection to the total indications found at the subsequent inspection (all indications reported in the prior cycle plus new indications). POPCD for the EOC n inspection (EOC,) is defined as:

EOCn+1 RPC EOC, bobbin confirmed plus detected, RPC not RPC confirmed plus inspected and not inspected bobbin detected + and repaired at at EOCn EOCn POPCD=

EOCn+1 RPC EOCn bobbin New EOCn+1 RPC confirmed plus + detected, RPC + confirmed or only not RPC confirmed plus RPC detected plus inspected and not inspected not RPC inspected bobbin detected and repaired at indications (i.e., not at EOCn EOCn detected at EOCn)

Notes for POPCD definition:

1. Rotating pancake coil (RPC) inspection is intended to include an RPC probe or equivalent such as a Plus Point coil.

2. RPC confirmed means a bobbin flaw signal was detected with a RPC probe.

3. Not RPC inspected means a flaw signal was detected with a bobbin probe and was not further inspected with a RPC probe.

4. EOCn bobbin indications that were RPC no detectable degradation (NDD) at EOCn, and at EOCn+, are either RPC detected or bobbin 5

Enclosure 1 PG&E Letter DCL-04-028 detected without RPC inspection, are treated as new indications (undetected at EOCn) for DCPP Units 1 and 2 POPCD, as previously requested by the NRC for DCPP Unit 2 Cycle 12 in NRC Question 1 of PG&E letter DCL-03-123.

This definition of POPCD is based on the premise that all indications that can contribute significantly to burst and leakage for voltage-based repair criteria application can be confirmed by RPC inspections. The term RPC is meant to include an RPC probe or equivalent, which includes a Plus Point coil. The POPCD definition that is used for ODSCC ARC analyses is based on RPC confirmed indications plus indications not RPC inspected.

EOC,+, RPC NDD results are excluded from POPCD. This application of the RPC results is applied to exclude from the POPCD method the probable false bobbin calls that would not contribute to tube integrity concerns at EOC.+ 1 for both previously reported and new indications. The use of RPC confirmation provides a measure of confidence that irrelevant prior and new bobbin calls are not allowed to influence the POD either as an increase or a decrease in the POD. The intent is that the EOCn+1 RPC should define the significance of the bobbin indication for POD considerations such that the insignificant RPC NDD indications are excluded from the POPCD method for both previously reported and new bobbin indications.

The POPCD method treats all new indications at an inspection as having been undetected at the prior inspection even though some of the new indications may have initiated during the operating cycle. The application of the POPCD method for operational assessment then accounts for newly initiated indications as well as previously undetected indications.

PG&E will apply the POPCD method using only the DCPP Units 1 and 2 inspection results because there is an adequate database to define a plant-specific POPCD. There have been seven ODSCC ARC inspections at DCPP, four on Unit 2 and three on Unit 1, such that there are five cycles of ARC operation where the POPCD method data can be evaluated (two from Unit I and three from Unit 2). Application of a plant specific POPCD method requires satisfaction of minimum data requirements for which guidelines were described in PG&E letter DCL-03-121 dated September 30, 2003. DCPP Units 1 and 2 meet these guidelines and, as such, a DCPP-specific POPCD distribution will be applied for ARC applications. Noise analyses performed for the two DCPP units did not show any significant differences in noise levels at TSP intersections between the two units. Since only DCPP data are applied for the proposed POPCD method, the noise data in the DCPP POPCD database directly applies for ARC applications.

6

Enclosure 1 PG&E Letter DCL-04-028 The single-cycle basis for the POPCD method evaluation assumes that large flaws would be detected during the EOCn+1 inspection. This assumption is supported by the industry POPCD database of 37 inspections. The multi-cycle development of a POPCD database over sequential inspections provides additional assurance that the potential for large undetected indications is included in POPCD. If an indication is undetected, it can be expected to grow over subsequent inspections to a detectable level. When detected, it is included at the BOC voltage as an undetected or new indication. As an example, for a 3-volt undetected indication, it can be expected that further growth would lead to detection at the next inspection and the indication would be included in the POPCD data as a 3-volt undetected indication. The largest undetected indication in the industry POPCD database is 3.2 volts, and the largest undetected indication in the DCPP database is less than 1.5 volts.

4.1.2 Classification of Indications and Assignment for POPCD Analyses Table 1 identifies all potential classifications for tracking bobbin coil indications between EOCn and EOC,+,. The classification of an indication is dependent upon whether the indication is bobbin detected at each cycle and whether the indication is confirmed by RPC inspection or not RPC inspected. The letters in the columns of Table I reflect the column for entering data in the Table 2 reporting format for POPCD data results. The format for reporting POPCD data reflected in Table 2 is used to develop the POPCD distributions following the guidelines described in this subsection. The columns provide the source of input data including the basis for defining the Cycle n voltage for the indications. Guidelines for assigning bobbin voltages to bobbin NDD indications are provided at the end of this subsection. The rows show the 0.1 voltage bin widths used for calculating the DCPP Units 1 and 2 POPCD distribution.

The Table 2 format is modified compared to Table 2 of letter DCL-03-109 (POPCD data table which provided NRC basis for Amendment No. 164 to Facility Operating License No. DPR-82) to reflect a standardization of terminology consistent with Table 1. The POPCD method calculation in Table 2 is unchanged from that in Table 2 of letter DCL-03-109. The DCPP Units 1 and 2 POPCD distribution curve is shown in Figure 1 (same as the UDCPP New NRC POPCD" curve in Figure 3 of letter DCL-03-109),

and the associated POPCD loglogistic regression parameters are provided in Table 5 (same as the "New NRC POPCD LogLogistic" table in Table 3 of letter DCL-03-109). The loglogistic regression parameters were defined in Section 4.2 of letter DCL-03-078.

Indications that were not detected at EOCr or EOCn+1 by the standard bobbin inspection, but that are detected during EOC,+, as a result of other RPC inspection activities are considered as new EOCn+ 1 RPC confirmed 7

Enclosure 1 PG&E Letter DCL-04-028 indications for the POPCD method analyses for EOCn (column F in Table 2). These indications will continue to be included as new indications in subsequent cycles unless the indication is reported in the normal bobbin coil inspection at a cycle following EOCn+1 . Thus, the indications will be considered as undetected at a minimum of two cycles, the EOCn and EOCn+1 inspections.

EOCn bobbin indications that were RPC NDD at EOCn, and at EOCn+1 are either RPC detected or bobbin detected without RPC inspection, are treated as new indications. This treatment of RPC NDD indications represents a departure from the generic POPCD methods described in EPRI Topical Report NP 7480-L, Addendum 5, but was necessary to obtain NRC approval of the POPCD method for DCPP Unit 2 Cycle 12, as discussed in PG&E's response to NRC Question 1 of PG&E letter DCL-03-123). In order to expedite NRC review of this LAR, it is again acceptable to PG&E to define the EOCn RPC NDD bobbin indications as undetected in the POPCD method calculations. There are three subsets of these indications reported in column G in Table 2: EOCn+1 bobbin indications detected by RPC, EOC,+ 1 bobbin indications with no RPC inspection; and EOCn+1 indications detected only by RPC inspection.

The following indications are considered to be false bobbin coil calls and are not included in the POPCD method analyses. The numbers are tabulated in column H in Table 2.

• Bobbin indications reported at EOCn but found to be NDD by RPC inspection at EOCn+i. EOCn bobbin indications confirmed by RPC at EOCn and found to be RPC NDD at EOCn+1 are not expected to occur but would be excluded from the POPCD method analyses if they would occur since the Cycle n+1 inspection would expect to find a larger indication if the EOC, indication was not a false call.

• Bobbin indications reported at EOCn but not found by the bobbin inspection at EOCn+1 . These indications are classified as indications not reportable (INR) and require resolution analysis to confirm that an indication is not present at EOCn+1 . Again, the Cycle n+1 inspection would expect to find a larger indication if the EOCn indication was not a false call.

• New bobbin indications reported at EOCn+1 but found to be NDD by RPC inspection at EOCn+i. RPC NDD indications at EOCn+1 are assumed to be false bobbin calls for POPCD method applications.

The following guidelines will be applied for determination of detection and bobbin voltages for the POPCD method analyses:

8

Enclosure I PG&E Letter DCL-04-028

• All determinations of detection at EOC, and voltages assigned to EOC, detected indications are to be based on the inspection records for the EOCn inspection.

• Lookback analyses are applied to assign voltages for new indications detected at EOCn+1 such that EOCn voltages are not available from the inspection records.

• For indications remaining bobbin NDD at EOCn by the lookback analyses, the EOCn bobbin voltage will be obtained by subtracting the average growth rate from the EOC,+ 1 voltage.

• When new EOCn+1 indications are found by RPC inspection but not reported as EOCn+1 bobbin indications, the voltages for EOCn+1 may be obtained by identifying the flaw based on a review of the 200 kHz data or by applying the DCPP Units 1 and 2 specific bobbin voltage to RPC voltage correlation. Guidance for these methods is provided in Section 10.1 of EPRI Topical Report NP 7480-L, Addendum 5. These methods are also applied to obtain bobbin voltages for EOCn indications found only by RPC and repaired at EOCn.

• If the RPC inspection identifies more than one ODSCC indication at the same TSP intersection, the bobbin voltage assigned to the TSP is estimated as the square root of the sum of squares for the bobbin voltages inferred from the RPC indications. This is an approximation to the effect on bobbin voltage of multiple indications around the tube circumference.

• Indications found only by RPC inspection in deplugged tubes returned to service at EOCn are included as new indications at EOCn if found by bobbin and/or RPC at the EOCn+i inspection.

4.1.3 Calculation of the POPCD Distribution The POPCD data is used in statistical generalized linear model regression analyses to develop a POPCD cumulative distribution function. The loglogistic fitting and Monte Carlo techniques previously described in Section 4.2 of letter DCL-03-078 are applied. The data are sorted into 0.1 volt bins representing various voltage levels, and the POPCD distributions are developed using fits to weighted binary data, where weighting is based on the number of indications in each bin. Monte Carlo techniques are then used to apply the POPCD curves to the distribution of indications found during the outage to develop the next cycle BOC indication voltage distribution. The Monte Carlo techniques include 9

Enclosure 1 PG&E Letter DCL-04-028 simulation of the POD uncertainties such that uncertainties in both the upper and lower tails of the POPCD distributions are adequately addressed.

The p-value from the POPCD regression analysis is the probability of observing a value of x2 as small as the one calculated from the data. If the p-value is found to be greater than 5 percent, i.e., the probability of randomly observing a value as small as the one calculated would be greater than 5 percent, a default value of POD of 0.6 will be applied. The associated implication is that there could be sufficient noise at the location of the indications to interfere with the detection of the indications. For the regression results of the DCPP-specific POPCD, the p-value was calculated to be effectively zero.

4.1.4 Continuing Assessment and Reporting for POPCD Upon implementation of POPCD, if the EOC conditional MSLB burst probability, the projected MSLB leak rate, or the largest indications (number and size) are underpredicted by the previous cycle operational assessment, the following guidelines will be applied to assess the need for methods adjustments:

• The probable causes for the underpredictions will be assessed and documented in the 90-day report. If the underpredictions are significant relative to the burst probability reporting threshold or site specific allowable leak rate, an assessment must be made of the potential need to revise the ARC analysis methods, and this assessment must be documented in the ARC 90-day report. A significant underprediction of burst probability is defined as 10 percent of the reporting threshold, i.e., 0.001. A significant underprediction of MSLB leak rate is defined as 0.5 gpm. A method assessment will also be made for smaller burst probabilities (e.g., underpredicted by less than 0.001) or leak rates (e.g., underpredicted by less than 0.5 gpm) if the condition monitoring results are underpredicted by an order of magnitude.

• An assessment will also be made for significant underestimates of the number of indications based on the following criterion. If the total number of as-found indications is underestimated by greater than 15 percent, a methods assessment will be performed to determine the cause and corrective actions will be proposed in the 90-day report.

The evaluation will include an assessment of the need to increase the number of predicted low voltage indications at the BOC to determine the effect on EOC projections. An underestimate of the less than 1 volt population when accompanied by an increase in the population above 10

Enclosure I PG&E Letter DCL-04-028 1 volt may be partially attributable to conservative growth rates which would increase the population above about 1 volt.

Historically, there have been no ARC cases where undetected indications (POD effects) have led to a challenge to structural or leakage integrity.

These cases have been associated with underpredictions in growth rates.

Growth rates will typically be the first potential cause examined for ARC underpredictions. Potential POD effects as the cause for underpredictions will also be assessed if the probable cause for the low predictions is a larger than anticipated undetected indication or due to cumulative numbers of indications above about 1 volt. The 90-day report will document any recommended changes to POD or growth methodology indicated by the assessments.

Upon implementation of POPCD, the following additional information will be included in the 90-day report:

• The composite multi-cycle POPCD data of Table 2 will be updated in the 90-day report, along with the associated Figure 1 POPCD distribution curve and the Table 5 POPCD method regression parameters, to include data from the just completed cycle. A separate POPCD data table and POPCD distribution curve will also be provided to include only data from the just completed cycle.

• The composite multi-cycle POPCD matrix data of Tables 3 and 4 will be updated in the 90-day report to include data from the just completed cycle. Separate POPCD matrix data tables will also be provided to include only data from the just completed cycle.

• To assess the POPCD method for potential changes over time, the 90-day report will compare the multi-cycle POPCD distribution applied for the last operational assessment with the POPCD distribution obtained for only the last operating cycle. Differences in the two POPCD distributions will be assessed relative to the potential for significant changes in detection capability.

• For RPC confirmed indications at EOCn that are RPC NDD at EOCn+1 ,

an assessment is required for the cause of the "disappearing flaws" if the Plus Point voltage is greater than 0.5 volt. If there are a significant number of occurrences of these "disappearing flaws", the cause will be evaluated independent of the Plus Point voltage.

In support of this evaluation, Table 1 requires an RPC inspection at EOCn+1 for RPC confirmed indications at EOCn (either bobbin detected or bobbin NDD) that are bobbin NDD at EOCn+1. This inspection is 11

Enclosure 1 PG&E Letter DCL-04-028 necessary to ensure that all known ODSCC indications are included in the condition monitoring and operational assessments as well as properly categorized for the POPCD method evaluation.

4.2 Growth Rate Considerations for POPCD Applications 4.2.1 Provision for Outlier Growth Rates Calculations applying the POPCD method or 0.6 as the POD will not predict flaws which result from voltage growth rates which are higher than previously seen (e.g. the R44C45-2H flaw which was detected as a 21.5-volt flaw at DCPP in the Unit 2 refueling outage 11 (2R1 1) inspection and was detected as a 2.0-volt flaw in Unit 2 refueling outage 10 and left in service per the ODSCC ARC repair criteria) and both POD methods lead to underestimates of the 2R1 I maximum flaw size, burst probability, and leak rate. The overly conservative and arbitrary application of a POD of 0.6 has not changed any assessments for corrective actions following identification of a large growth rate indication. For smaller growth rate underpredictions, the application of a POD of 0.6 can mask a real growth rate issue by leading to artificially high burst and leakage predictions with an associated conclusion that no corrective action is necessary.

A high voltage growth rate can be expected to periodically occur and cannot be predicted for a specific cycle. Normal growth in depth can lead to a large voltage increase when the upper range of depth growth occurs for a near throughwall or short throughwall indication. This occurs as the result of the exponential dependence of voltage on depth and again on throughwall length and is inherent to the voltage-based methods for tube integrity assessments. For many occurrences of large growth rates with associated large EOC voltages, the indications have been pulled and destructively examined. When the largest indications found in ARC inspections have been destructively examined, all indications have demonstrated burst pressures exceeding APMSLB and leak rates generally consistent with the ARC correlations.

Preliminary ARC guidelines have been drafted by EPRI to address preventive repair of ODSCC indications at less than the ARC repair limit to reduce the likelihood of finding a large voltage indication at the next inspection. Specifically, for 7/8 inch tubing, the draft guidelines suggest that consideration be given to preventive repair of ODSCC indications found to have a Plus Point maximum voltage greater than or equal to 1.9 volts (1.9 Plus Point volts corresponds to about 95 percent maximum ODSCC depth based on applying a typical amplitude sizing correlation).

To ensure that greater than or equal to 1.9 volt Plus Point indications are detected, the guidelines recommend an augmented inspection program.

12

Enclosure 1 PG&E Letter DCL-04-028 Since a Plus Point to bobbin voltage ratio of about 1.1 bounds most ODSCC indications, the guidelines suggest that a 20 percent Plus Point sample inspection be performed for indications greater than 1.7 bobbin volts. If this sample inspection of bobbin indications between 1.7 volts and the 7/8 inch GL 95-05 repair limit of 2.0 volts identifies Plus Point indications greater than 1.9 volts, the inspection should be expanded to include all bobbin indications between 1.7 and 2.0 volts.

If a plant applies locked TSPs to prevent burst and has a repair limit greater than the GL 95-05 limits, there is no need to apply the above preventive repair guidelines unless leakage from a single large voltage indication would potentially cause leakage limits to be exceeded.

The EPRI guidelines and technical basis are targeted for NRC submittal in April 2004. Since the guidelines apply to preventive repair, implementation of these guidelines is optional on a plant specific basis.

PG&E has elected to adopt these guidelines starting in April 2004 inspections (1R12), and the DCPP implementing procedure has been revised to incorporate the guidelines.

EPRI is also developing an outlier growth method for application to ODSCC ARC coincident with the use of the POPCD method. Upon completion of the method development, expected by April 2004, the outlier growth methodology will be submitted to the NRC, and PG&E will provide the NRC with revised EOC 12 projections and EOC 13 projections using the outlier growth method. Upon NRC approval to use the POPCD method for ODSCC ARC applications for DCPP Units 1 and 2, PG&E will adopt the outlier growth method for application to ODSCC ARC coincident with the use of the POPCD method.

4.2.2 Development of Growth Rate Distributions Conservative growth rates should be used in the operational assessments for ARC analyses. The outlier growth method noted above is one technique for adding conservatism to the growth distributions. GL 95-05 requires the use of the most limiting of the two previous growth rate distributions for the next operating cycle, and WCAP-14277, Revision 1, recommends that the more conservative growth (relative to predicting leakage and burst) between the distributions for the specific SG, and for all SGs collectively, should be used.

GL 95-05 notes that a single growth distribution in terms of delta volts rather than percent delta volts can be used provided the conservatism of this approach continues to be supported by operational experience. This requires an assessment for the potential onset of voltage dependent growth (VDG). The onset of VDG can generally be seen from plots of 13

Enclosure 1 PG&E Letter DCL-04-028 voltage growth versus BOC voltage. The occurrence of a higher frequency of large growths or increased growth rates with increased BOC voltage is an indication of the presence of VDG. Methods for calculating VDG distributions are described in Attachment 2 to Enclosure 4 of PG&E letter DCL-03-076 dated June 23, 2003. These methods define techniques for determining break points in voltage bins with each bin defining a separate growth distribution. At DCPP Units 1 and 2, the onset of VDG has been identified and the VDG methods are being applied for operational assessments.

4.3 Benchmarking of POPCD DCPP Unit 1 and DCPP Unit 2 multiple cycle benchmarking analyses were performed and the results support the adequacy of the POPCD methodology for ARC applications at DCPP Units 1 and 2. These analyses were submitted to the NRC in PG&E letter DCL-04-019, dated March 16, 2004, for DCPP Unit 1, and PG&E letter DCL-03-121 dated September 30, 2003, for DCPP Unit 2. Both the DCPP Unit 1 and Unit 2 analyses address NRC questions contained in PG&E letter DCL-03-121.

The results of the POPCD method benchmarking analyses indicate that the methodology used to predict EOC conditions is generally conservative.

For DCPP Unit 1, the prior cycle benchmarking results show that the methodology used to predict EOC leak rate and POB is conservative in all cases. For DCPP Unit 2, some predictions were not conservative, but the underpredictions were not significant relative to the as-found inspection results. Underpredictions when applying the POPCD method are more likely to be due to growth rate uncertainties than POPCD method uncertainties. DCPP Unit 2 benchmarking results show that use of a constant POD of 0.6 results in excessively conservative projections and would have entirely masked the increased growth rate issues for Unit 2 Cycle 11 if the 21.5-volt R44C45-2H indication had not occurred.

Extensive industry benchmarking using the POPCD method has been performed and documented in EPRI Topical Report NP 7480-L, Addendum 5, and showed that POPCD method projections were in agreement with the actual EOC voltage distribution. The results show that use of a constant POD of 0.6 is nonconservative below about 0.5 volts and very conservative above 1 volt, which leads to excessively conservative probability of burst and leakage predictions.

The DCPP POPCD method results for bobbin coil detection are in good agreement with POD results obtained from the industry POPCD results, Argonne National Lab round-robin testing, and an EPRI POD obtained from blind testing of analysts.

14

Enclosure I PG&E Letter DCL-04-028 4.4 Conclusions The current licensed ARC methodology of using a uniform POD value of 0.6, based on GL 95-05, results in an overly conservative and counter intuitive estimate of the number and severity of indications remaining in the SGs following the inspection. The POPCD method is a more realistic POD that is a function of indication voltage.

Based on industry and DCPP-specific bobbin detection data for ODSCC within the SG TSP region, large voltage bobbin indications that can individually challenge structural or leakage integrity can be detected with near 100 percent certainty and would not be left in service. These large voltage indications should not be included in the BOC voltage distribution, other than as inferred from the voltage dependent POD, for the purpose of the operational assessment. The POPCD method approach to POD considers the potential for missing indications that might challenge structural or leakage integrity by applying the POPCD data from successive inspections. The DCPP Units 1 and 2 POPCD database includes data from at least 3 successive inspections for each unit. If a large indication was missed in one inspection, it would continue to grow until finally detected in a later inspection. Therefore, the use of the POPCD method to determine the BOC voltage distribution will improve EOC projections and lead to appropriate estimates of the margin in SG tube structural and leakage integrity. Application of the POPCD method reduces preventive plugging of SG tubes which maintains reactor coolant system flow margin and reduces personnel dose during refueling outages.

5.0 REGULATORY ANALYSIS

5.1 No Significant Hazards Consideration PG&E has evaluated whether or not a significant hazards consideration is involved with the proposed amendment by focusing on the three standards set forth in 10 CFR 50.92, "Issuance of amendment," as discussed below:

1. Does the proposed change involve a significant increase in the probability or consequences of an accident previously evaluated?

Response: No.

The use of a revised steam generator (SG) voltage-based repair criteria probability of detection (POD) method, the probability of prior cycle detection (POPCD) method, to determine the beginning of cycle (BOC) indication voltage distribution for the Diablo Canyon Power Plant (DCPP)

Units 1 and 2 operational assessments does not increase the probability 15

Enclosure 1 PG&E Letter DCL-04-028 of an accident. Based on industry and plant specific bobbin detection data for outside diameter stress corrosion cracks (ODSCC) within the SG tube support plate (TSP) region, large voltage bobbin indications which individually can challenge structural or leakage integrity can be detected with near 100 percent certainty. Since large voltage ODSCC bobbin indications within the SG TSP can be detected, they will not be left in service, and therefore these indications should not be included in the voltage distribution for the purpose of operational assessments. The POPCD method improves the estimate of potentially undetected indications for operational assessments, but does not directly affect the inspection results. Since large voltage indications are detected, they will not result in an increase in the probability of a steam generator tube rupture (SGTR) accident or an increase in the consequences of a SGTR or main steam line break (MSLB) accident.

Therefore, the proposed change does not involve a significant increase in the probability or consequences of an accident previously evaluated.

2. Does the proposed change create the possibility of a new or different accident from any accident previously evaluated?

Response: No.

The use of the POPCD method to determine the BOC voltage distribution for the DCPP Units 1 and 2 operational assessments concerns the SG tubes and can only affect numerical predictions of probabilities for the SGTR accident. Since the SGTR accident is already considered in the Final Safety Analysis Report Update, there in no possibility to create a design basis accident that has not been previously evaluated.

Therefore, the proposed change does not create the possibility of a new or different accident from any accident previously evaluated.

3. Does the proposed change involve a significant reduction in a margin of safety?

Response: No.

The use of the POPCD method to determine the BOC voltage distribution for the DCPP Units 1 and 2 operational assessments does not involve a significant reduction in a margin of safety. The applicable margin of safety potentially impacted is the Technical Specification 5.6.10, "Steam Generator (SG) Tube Inspection Report," projected end-of-cycle leakage for a MSLB accident and the projected end-of-cycle probability of burst.

Based on industry and plant specific bobbin detection data for ODSCC within the SG TSP region, large voltage bobbin indications that can 16

Enclosure 1 PG&E Letter DCL-04-028 individually challenge structural or leakage integrity can be detected with near 100 percent certainty and will not be left in service. Therefore these indications should not be included in the voltage distribution for the purpose of operational assessments. Since these large voltage indications are detected, they will not result in a significant increase in the actual end-of-cycle leakage for a MSLB accident or the actual end-of-cycle probability of burst. The POPCD method approach to POD considers the potential for missing indications that might challenge structural or leakage integrity by applying the POPCD data from successive inspections. If a large indication was missed in one inspection, it would continue to grow until finally detected in a later inspection.

Based on the above evaluation, PG&E concludes that the proposed change presents no significant hazards consideration under the standards set forth in 10 CFR 50.92(c), and accordingly, a finding of "no significant hazards consideration" is justified.

5.2. Applicable Regulatory Requirements/Criteria GL 95-05 requires the application of a POD of 0.6 to all previous bobbin indications for the determination of the indication voltage distribution for the BOC, unless another POD methodology is approved by the NRC.

This LAR requests NRC approval to use another POD methodology.

Therefore, the use of another POD methodology approved by the NRC will continue to meet the requirements of GL 95-05.

In conclusion, based on the considerations discussed above, (1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public.

6.0 ENVIRONMENTAL CONSIDERATION

PG&E has evaluated the proposed amendment and has determined that the proposed amendment does not involve (i) a significant hazards consideration, (ii) a significant change in the types or significant increase in the amounts of any effluent that may be released offsite, or (iii) a significant increase in individual or cumulative occupational radiation exposure. Accordingly, the proposed amendment meets the eligibility criterion for categorical exclusion set forth in 10 CFR 51.22(c)(9). Therefore, pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the proposed amendment.

17

Enclosure I PG&E Letter DCL-04-028

7.0 REFERENCES

1. Generic Letter 95-05, 'Voltage-Based Repair Criteria for Westinghouse Steam Generator Tubes Affected by Outside Diameter Stress Corrosion Cracking," dated August 3, 1995

2. PG&E letter DCL-97-034, "License Amendment Request 97-03, Voltage-Based Alternate Steam Generator Tube Repair Limit for Outside Diameter Stress Corrosion Cracking at Tube Support Plate Intersections,"

dated February 26, 1997

3. NRC Letter for Amendment Nos. 124 and 122 for Diablo Canyon Power Plant Units I and 2 respectively, "Issuance of Amendments for Diablo Canyon Nuclear Power Plant, Unit No. 1 (TAC No. M97254) and Unit No. 2 (TAC No. M97255)," dated March 12, 1998

4. EPRI Topical Report NP 7480-L, Addendum 5, "Steam Generator Tubing Outside Diameter Stress Corrosion Cracking at Tube Support Plates Database for Alternate Repair Limits, Update 2002," dated January 2003

5. Nuclear Energy Institute Letter, A. Marion (NEI) to Document Control Desk (NRC), "Steam Generator Degradation Specific Management Database, Addendum 5," dated February 13, 2003

6. WCAP-14277, Revision 1, "SLB Leak Rate and Tube Burst Probability Analysis Methods for ODSCC at TSP Intersections," dated December 1996

7. NUREG-0844, "NRC Integrated Program for the Resolution of Unresolved Safety Issues A-3, A-4, and A-5 Regarding Steam Generator Tube Integrity"

8. PG&E letter DCL-03-076, "Special Report 03 Results of Steam Generator Inspections for Diablo Canyon Power Plant Unit 2 Eleventh Refueling Outage," dated June 23, 2003

9. PG&E letter DCL-03-078, "License Amendment Request 03-10, Revised Steam Generator Voltage-based Repair Criteria Probability of Detection Method for Diablo Canyon Unit 2 Cycle 12," dated June 26, 2003

10. PG&E letter DCL-03-109, "Supplemental Information to Support License Amendment Request 03-10, 'Revised Steam Generator Voltage-based Repair Criteria Probability of Detection Method for Diablo Canyon Unit 2 Cycle 12,"' dated September 3, 2003

11. PG&E letter DCL-03-123, "Response to NRC Request for Additional Information Regarding License Amendment Request 03-10, 'Revised Steam Generator Voltage-based Repair Criteria Probability of Detection Method for Diablo Canyon Unit 2 Cycle 12,"' dated September 30, 2003

12. PG&E letter DCL-03-121, "PG&E Response to NRC Questions on 2R11 Steam Generator Tube Inspections," dated September 30, 2003

13. NRC Letter for Amendment No. 164 for Diablo Canyon Power Plant Unit 2, "Diablo Canyon Nuclear Power Plant, Unit No. 2 - Issuance of Amendment -

Revised Steam Generator Voltage-based Repair Criteria Probability of Detection Method for Diablo Canyon Unit 2 Cycle 12 (TAC No. MB9742),"

dated October 21, 2003

14. PG&E letter DCL-04-019, "DCPP Unit 1 Voltage-Based Repair Criteria Benchmarking and EOC-12 Projections," dated March 16, 2004 18

Enclosure 1 PG&E Letter DCL-04-028 Table I - POPCD Matrix Table for Tracking Indications Between EOC, and EOC~,,

l BDD at EOCn+ 1 BND at EOCn,1 EOCn BDD w/o RPC BDD w/RDD BDD w/RND BND w/o RPC BND w/RDD BND w/RND Not Not Not Not Not Not l Plugged

= Plugged Plugged Pgugged Plu gged Plugged Plugged Plugged Plugged d Plugged Plugged C _

BDD BDD w/o RPC Not Plugged B B A A H H H H A A H H at BOO wI ROD Plugged C____ ___

EOCn Not Plugged C B B A A H (2) H (2) H (1) H(1) A A H (2) H(2)

BDD w/ RND Plugged H _ l l Not Plugged G (3) G (3) G (3) G (3) H H H H G (3) G (3) H H Plugged  :: I BND w/o RPC Not Plugged _ E E D D H H No Count No Count F F No Count No Count BNDJ at BND w/ RDD Plugged F _  : _ V EOCn Not Plugged E E D D H(2) H(2) H(1) H (1) F F H (2) H(2)

BND wi RND Plugged II ._ . ._._ _-_=_.

I Not Plugged E E D D H H No Count No Count F F No Count No Count General Notes:

The column letters correspond to the column letters in POPCD Table 2.

BDD = Bobbin detected indication BND = Bobbin no detectable degradation (NDD) intersection RDD = RPC detected indication RND = RPC no detectable degradation intersection No Count = Intersections having no bobbin or RPC indication at either EOCn or EOCn+o. These are not needed for POPCD.

Sgecific Notes:

1) For EOCn bobbin indications that are confirmed by RPC or detected only by RPC, EOCn+1 RPC will be performed when bobbin is NDD and the number in this category will be "0"for future inspections.

2) If indications are RPC confirmed at EOCn but RPC NDD at EOCn+,, and the Plus Point voltage is greater than 0.5 volts the causative factors for this change in RPC detection will be discussed in the ARC 90-day report. If there are a significant number of these occurrences of this category, independent of the Plus Point voltage, the cause will be evaluated in the 90-day report.

3) EOCn bobbin indications that were RPC NDD at EOCn, and at EOCn+1 are either RPC detected or bobbin detected without RPC inspection, are treated as undetected at EOCn in accordance with NRC request.

19

Enclosure 1 PG&E Letter DCL-04-028 Columrn A I B l C I D I E I I G I H I I I J I K Table 2. POPCD Data Table Delectles et FCM Pk D sdeu t EOCOll(Nw bbdloadlws4 EOC,Bobbinbd. MPC IOC Bbbin.

COnfRiNe£4EOC.A BDD~onf I a~fR IBPM.

R b

d. RC E

etrA NoIRPC IOCA Bobbin1d. RepairedSt BDflMl.D RPC EOCA 0( IBDD I PM - cm.-d .t IwEOC.,,BobbiPC Iw ABND CoII_

sru . RPC _OP

_w

- BDD,/ RDD N OC., BolbilotRPC w.Fu4Only byWRPC

-nrA BNh/fCflflfP pI #rvu AM -v U~~u uu-_

NlflP n a EOC FM Sp -r lrto

_N ....

vtEOC.

E I

wIr EOC Rnn Knrunu u

IMP, i.

fD

_uIvD>

uu _

Dobbie MMRPC u

1 r

j Endude kim

.U DU- VP.lICI Trabi or POPCD POP CD Evuagalrn Vu" .. BID/RD _-NI/RDO BO I MRD -_BDD W RPC BOwo RPC -bPlggOd at EDC OND/RWD-_ B0,/D BNW IDD _BDD o-RPC BN/ROD _ BNDIRDO BIDDIRND _ EOO/ROD All BND sRPC IOoDndon IM POPCD f r Bin IBWo RPeC _. W0/ROD BN/ R _ORM

-RN D BNDI RNO-* BDD*o RPC BFND I RND_ NDI RDD_ OO/RHO -* I ROD t EOCn+1 t EOCr Detdctv Volftr Bin PM d.iAOW -*RiniI M F/ND I RW , Plumedd ECn nI IEOCa iNoitni 1

0 37 061060 I -

.31-1.40 7

I 0a 1,OD01 1.000 1.00C IcO 100 1 amV 3 41-3.50 .

4.114.20 . 1 Wm 4B1-490 9

1) POPCD foreachvolia bincalculated an(Detection A EOCnDetdction atEOCn+ NoDdthtionat EOCr)Bycolirm, POPCD * (A4B+W.B6C.DnE+F+G)'

21EOCnRPCUWDbobbin indications air tnaad ds newindicitionsptr NRC rquest

3) Incledusindicalions a EConpugd r EOCnrmdnowindications at EOCn+l,notreportedinIh bobbin inspection.

andbund onlyby RPCiactionfd derms. rmxd residuals orother asonsforth RPCminpetion.

m ann . Oa. 4...- -- l - . O.hk i- rn- I- - r-or ---

1.

r , .-.-. fr - -

20

Enclosure I PG&E Letter DCL-04-028 Table 3 - DCPP Units I and 2 POPCD Matrix for Indications in Three Voltage Bins POPCD Matrix for Indications <=1 .00v at EOCn

__ _ OO at EOCn+1 S__ _ _ _ _ _ _ _ _ E__ND at EOCn+1 _ _ _ _ _

___________________Plugged 1 Plugged I Plugged Plugged Plugged JPlugged Plugged Plu~ggead Plugged1 Plugged Plugged Plugged Plugged 11 _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ _ _ _ _ _

BDD BDD wtoRPC Not Plugged ____ 40 968 132 158 0 33 0 24 0 0 0 0 at ADD wI RDD Plugged 43 __ __ _ __ _ _ _ _ _

EOnNot Plugged ___ 1 242 17 185 0 I 0 0 0 4 0 1 EOnBDO wIRND Plugged 2 ________

___Not Pluged 3 66 7 33 0 48 0 30 0 0 0 3 Plugged__ _ _ __ _ _ __ _ _ __ _ ___ _ _ __ _ _ __ _ __ _ _ _

BND SNDw/oRPC NotPlugged 43 1721 89 420 4 88 1No Count No Count 24 91 No Count No Count at BN IRDD Plugged 18 __ __ __ _ __ _ __ _ _ _

______Not Plugged 0 2 0 1 oCutN on 1 N on oCu Eocn Pi_ ed__ _

_____ _____ ____ POPCD Matrix for Indications >11.00v and <=2.00v at EOCn_ _ _ _ _ _ _ _ _

___BOO at EOCn+1 - OND at EOCn+1 EOnBDDw/RPC I SDD DD I BDD wQ~/RND BNDwRPo I SAIDwDID A NDwRN 1

_________________ Plugged Plugged Plugged Plugged JPluggedJ Pluggedj Plugged Plugged Plugged Plugged Plugged Plugged Plugged 9 _ _ __ _ _ _ _ _ _ _ _ _ _ _

BDD ADD w/oRPC Not Plugged _ 0 52 130 4 0 2 0 0 0 0 0 0 at BDD wIRDD Plu ged 3 _ __ _ _ _ _ _ _ _ _

EOnNot Plugged __ 1 25 is 7 0 0 0 0 0 0 0 0 E DO wRND Plugged I-

_______ Not Plugged ___ 0 1 0 1 0 2 0 0 0 0 0 0 Plugg d I_______-[N 1BNO AND wlo RPC Not lugd0 14 3 11 1 3 NoCuntl No Count[ 0 0 NCount No Count at AND wI RDD Pued 0 _____ ____

EOCn Not Piued0 0 0 0 0 ONoCountl No Countl 0 No Cont No Co BN_____w otPlggdD 0 0 0 0 0 NoCunt! 0 No Con0 NoCutoon

______ _____ _____ _____ _____POPCD Matrix for Indications >2.00v at EOCn _ _ _ _ _ _ _ _ _

_______ DOat EOCn+1 -BND at EOCn+1 __

EOnPugd

_uggd AOnDDw/RPC Plugged__

Not Plugged ADD w/DD (Not j I ADD w/RND N-ot- j BNDw RPC I Plugged Plugged Plugged Plugged Plugged Plugged Plugged Plugged Not NDwIRDD N IAND w/RND d Plugged No Plugged 0 _ _ _ _ _ __ _ _

EBDD BDD w16RPC Not Plugged ___ 0 0 0 0 0 0 0 0 0 0 0 0 at BDD wIRDD Plungd 32 __

EOnNot Plugged 0 0 0 0 0 0 0 0 0 0 0 0 AOn DD wI RND Plugged 0 __

Not Plunged ___ 0 0 0 0 0 0 0 0 0 0 0 0 BND AND wlo RPC Not Plugged I___ 0 0 0 0 0 0 No Count No Count 0 0 No Count No Count at AND w/ RDD Plugged 0 ___ _ _ I-_ _ _

EOnNot Plugged o___ 0 0 0 0 0 No Count No Count 0 0 No Count No Coun ENOIRNnPugged _ _ _ _ _ _ _ I_ _ _ _ _ _ _

BN /RDNot Plugg~ed 0 0-O 0 0 0 10 1No Counti No Count 0 0 No Count! No Coung ADD = Bobbin detected indication AND = Bobbin NDD intersection RDD = RPC detected indication RND = RPC NDD intersection 21

Enclosure 1 PG&E Letter DCL-04-028 Table 4 - DCPP Units I and 2 POPCD Matrix for All Indications POPCD Matrix for All Indications BDD at EOCn, 1 BND at EOCn, 1 EOCn BDD w/o RPC BDD w/RDD BDD w/RND BND w/o RPC BND w/RDD BND w/RND Pu P

I Not Not d Plugged Plugged Plugged Plug d_

Not Not Not Not Plugged Plugged Plugged Plugged Plugged Pluged Plugged Plugged 20 _

BD BDD w/o RPC Not Plugged _ 40 1020 262 162 0 35 0 24 0 0 0 0 at BDD w/RDD Plugged 78 .

EOCn Not Plugged _ 2 267 32 192 0 1 0 0 0 4 0 1 BDD wI RND Plugged 3 _

_____D Not Plugged 3 67 7 34 0 50 0 30 0 0 0 3 Plugged  : I_ _i_

BND w/o RPC Not Plugged 43 1735 92 431 5 91 No Count No Count 24 91 No Count No Count at BND wI RDD Plugged 18 _.

EOCn Not Plugged _ 0 2 0 11 0 0 No Count No Count 3 21 No Count No Count BND WI RND Plugged _I I _I nt Nooun Not No Plugged Pluged 0 1 1

3 r 5

5l r 0 5 No Count No Count 11 7 No Count No Count ns BDD = Bobbin detected indication BND = Bobbin no detectable degradation intersection RDD = RPC detected indication RND = RPC no detectable degradation intersection No Count = Intersections having no bobbin or RPC indication at either EOCn or EOC,+ 1 . These are not needed for POPCD.

22

Enclosure 1 PG&E Letter DCL-04-028 Table 5: DCPP-Specific POPCD LogLogistic Parameters Parameter LogLogistic Number of Data Points 4688 a.0 (intercept) 1.644 a.1 (slope) 4.659 VI1 0.00522 V12 0.01043 V22 0.02654 Deviance 5221 MSE 0.1890 Binary TRUE Chi-Square 885.5 Degrees of Freedom 4686 p-Value <2.9E-07 23

Enclosure 1 PG&E Letter DCL-04-028 Figure 1 DCPP Units 1 and 2 POPCD Distribution Approved for Unit 2 Cycle 12 in LA 164 1.0 -_

0.9 _

0.8 -_

i 0.7-0 _

, 0.6 vC

, 0.5 I.- -

Cl

0.4 S._

C; a-0.2 0.1 _

0.0 0.1 1.0 10.0 Bobbin Coil Volts 24

Enclosure 2 PG&E Letter DCL-04-028 Final Safety Analysis Report Update Markup (For information only)

DCPP UNITS 1 & 2 FSAR UPDATE 6.5.2.5.4 Voltage-Based Alternate Repair Criteria The voltage-based repair limits in the Technical Specifications implement the guidance in GL 95-05 and are applicable only to Westinghouse-designed SGs with outside diameter stress corrosion cracking (ODSCC) located at the tube-to-tube support plate intersections. The voltage-based repair limits are not applicable to other forms of SG tube degradation nor are they applicable to ODSCC that occurs at other locations within the SG. Additionally, the repair criteria apply only to indications where the degradation mechanism is dominantly axial ODSCC with no significant cracks extending outside the thickness of the support plate. Refer to GL 95-05 for additional description of the degradation morphology.

The lower voltage repair limit for 7/8 inch diameter SG tubing is 2.0 volts in accordance with GL 95-05. Calculation of the upper voltage repair limit requires a derivation of the voltage structural limit from the burst versus voltage empirical correlation and then the subsequent derivation of the upper voltage repair limit from the structural limit.

The voltage structural limit is the voltage from the burst pressure/bobbin voltage correlation, at the 95 percent prediction interval curve reduced to account for the lower 95/95 percent tolerance bound for tubing material properties at 6500F (i.e., the 95-percent LTL curve). The voltage structural limit must be adjusted downward to account for potential flaw growth during an operating interval and to account for NDE uncertainty. The upper voltage repair limit, VURL, is determined from the structural voltage limit by applying the following equation:

VURL = VSL - VGR - VNDE where VGR represents the allowance for flaw growth between inspections and VNDE represents the allowance for potential sources of error in the measurement of the bobbin coil voltage. Further discussion of the assumptions necessary to determine the upper voltage repair limit are discussed in GL 95-05.

The upper voltage repair limit mid-cycle equation in GL 95-05 and in the Technical Specifications should only be used during unplanned inspections in which eddy current data is acquired for indications at the tube support plates.

For the operational assessment for Unit I and Unit 2, the Probability Of Prior Cycle Detection (POPCD) voltage-based probability of detection (POD) method, as described in letter DCL-04-028, is used to determine the beginning of cycle voltage distributions. The POPCD method is an exception to the GL 95-05 guidance that requires the application of a POD of 0.6 to all previous bobbin indications. The use of the POPCD method for the Unit 1 and Unit 2 operational assessments was approved by the NRC in amendments / to the Unit 1 and Unit 2 Operating Licenses.

The Technical Specifications implement several reporting requirements recommended by GL 95-05 for situations which the NRC wants to be notified prior to returning the SGs to service.

For the purposes of this reporting requirement, leakage and conditional burst probability can be calculated based on the as-found voltage distribution rather than the projected end-of-cycle voltage distribution (refer to GL 95-05 for more information) when it is not practical to complete these calculations using the projected EOC voltage distributions prior to returning the SGs to service. Note that if leakage and conditional burst probability were calculated using the measured EOC voltage distribution for the purposes of addressing the GL Section 6.a.1 and 6.a.3 reporting criteria, then the results of the projected EOC voltage distribution should be provided per the GL Section 6.b(c) criteria.