ML082760283

Attachments 1 & 2, Calvert Cliffs Nuclear Power Plant Inc., Proposed Alternative ISI-020, and Proposed Alternative ISI-021

ML082760283
Person / Time
Site:	Calvert Cliffs
Issue date:	10/01/2008
From:	Constellation Energy Group
To:	Office of Nuclear Reactor Regulation
Shared Package
ML08260280	List: ML082760283
References
Download: ML082760283 (11)

Text

ATTACHMENT (1)

PROPOSED ALTERNATIVE ISI-020 Calvert Cliffs Nuclear Power Plant, Inc.

October 1, 2008

ATTACHMENT (1)

PROPOSED ALTERNATIVE ISI-020 American Society of Mechanical Engineers (ASME) Code Component(s) Affected The affected component is the Calvert Cliffs Nuclear Power Plant (CCNPP) Unit 2 reactor pressure vessel (RPV), specifically the following ASME Boiler and Pressure Vessel (BPV) Code Section XI (Reference 1) examination categories and item numbers covering examinations of the RPV. These examination categories and item numbers are from IWB-2500 and Table IWB-2500-1 of the ASME BPV, Code Section XI.

Examination Category Item No. Description B-A B1.11 Circumferential Shell Welds B-A B1.12 Longitudinal Shell Welds B-A B1.21 Circumferential Head Welds B-A B1.22 Meridional Shell Welds B-A B1.30 Shell-to-Flange Weld B-A B1.40 Head-to-Flange Weld B-D B3.90 Nozzle-to-Vessel Welds B-D B3.100 Nozzle Inner Radius Areas (Throughout this request the above examination categories are referred to as the subject examinations and the ASME BPV Code,Section XI, is referred to as the Code.)

Applicable Code Edition and Addenda

American Society of Mechanical Engineers Code Section XI, Rules and Inservice Inspection of Nuclear Power Plant Components, 1998 Edition (no Addenda).

Applicable Code Requirement

IWB-2412, Inspection Program B, requires volumetric examination of essentially 100% of RPV pressure retaining welds identified in Table IWB-2500-1 once each ten-year interval and also requires a surface exam of the head-to-flange weld. The Calvert Cliffs Unit 2 Third Ten-Year Inservice Inspection (ISI) interval is scheduled to end June 30, 2009.

Reason for Request

An alternative is requested from the requirement of IWA-2412, Inspection Program B, that the subject examinations of essentially 100% of RPV pressure retaining welds, examination categories B-A and B-D welds, be performed once each ten-year interval. Extension of the inspection interval for examination categories B-A and B-D welds from 10 years to up to 20 years will result in a reduction in personnel radiation exposure and examination costs.

Proposed Alternative and Basis for Use Calvert Cliffs Nuclear Power Plant proposes to defer the ASME Code required subject examinations of the Unit 2 RPV full penetration pressure retaining examination categories B-A and B-D welds for the third ISI interval until 2019 and to perform the fourth ISI of these welds on a 20-year inspection interval, instead of the current ten-year inspection interval. Therefore, the fourth ISI is proposed to be performed in 2039. These dates are consistent with the information provided to the Staff in Pressurized Water Reactor Owners Group letter OG-06-356 (Reference 2).

1

ATTACHMENT (1)

PROPOSED ALTERNATIVE ISI-020 In accordance with 10 CFR 50.55a(a)(3)(i), the proposed alternate inspection interval, which provides an acceptable level of quality and safety, is requested on the basis that the current inspection interval can be extended based on a negligible change in risk by satisfying the risk criteria specified in Regulatory Guide 1.174 (Reference 3).

The methodology used to demonstrate the acceptability of extending the third and fourth ISI intervals for examination categories B-A and B-D welds based on a negligible change in risk is contained in WCAP-16168-NP-A, Revision 2 (Reference 4). This methodology was used to develop a pilot plant analysis for Westinghouse, Combustion Engineering, and Babcock and Wilcox reactor vessel designs and is an extension of the work that was performed as part of the Nuclear Regulatory Commission Pressurized Thermal Shock (PTS) Risk Re-Evaluation (Reference 5). The critical parameters for demonstrating that this pilot plant analysis is applicable on a plant specific basis, as identified in WCAP-16168-NP-A, Revision 2, are identified in Table 1. By demonstrating that each plant specific parameter is bounded by the corresponding pilot plant parameter, the application of the methodology to the Calvert Cliffs Unit 2 RPV is acceptable. The comparison of pilot plant parameters and plant specific parameters is shown in Table 1 below.

Table 1. Critical Parameters for Application of Bounding Analysis Additional Plant Specific Evaluation Parameter Pilot Plant Basis Basis Required?

Dominant PTS Transients in the No NRC PTS Risk Study PTS Generalization NRC PTS Risk Study are (Reference 5) Study (Reference 6) applicable 2.89E-10 Events per No Through Wall Cracking 3.16E-7 Events per year year (Calculated per Frequency (Reference 1)

Reference 5)

Bounded by 13 No Frequency and Severity of Design 13 heatup/cooldowns per heatup/cooldowns Basis Transients year (Reference 1) per year Cladding Layers No Single Layer (Reference 1) Single Layer (Single/Multiple)

Additional information relative to the Calvert Cliffs Unit 2 RPV inspection is provided in Table 2. This information confirms that satisfactory examinations have been performed on the Calvert Cliffs Unit 2 RPV.

2

ATTACHMENT (1)

PROPOSED ALTERNATIVE ISI-020 Table 2. Additional Information Pertaining to RPV Inspection Inspection methodology: ASME Section XI and Regulatory Guide 1.150 (Reference 7) inspections were Performance Demonstration Initiative (PDI) qualified per Reference 8 and were therefore performed in accordance with the requirements of ASME Section XI Appendix VIII.

Number of past inspections: All welds have been inspected at least twice with the exception of 5 lower head Meridional welds which have been inspected once.

Number of indications found: A total of 9 indications were detected in the most recent ISI. All 9 indications are acceptable in accordance with IWB-3500 of Section XI of the ASME Code. Four of these indications are located in the reactor vessel beltline region. Three of these indications meet the Allowable Number of Flaws requirements for the proposed voluntary PTS Rule (10 CFR 50.61a) in SECY-07-0104 (Reference 9). One indication, in plate material with a through-wall extent of 0.60, does not meet the requirements in SECY-07-0104.

Additional information regarding this flaw is provided in Table 3 below.

Proposed inspection schedule The third ISI is currently scheduled for 2009. The third ISI is for balance of plant life: proposed to be performed in 2019. The fourth ISI is proposed to be performed in 2039.

Table 3 provides additional information relative to the calculation of the through wall cracking frequency (TWCF) parameter for Calvert Cliffs Unit 2.

Table 3. Details of TWCF Calculation at 60 EFPY Inputs Reactor Coolant System Temperature, TRCS[°F]: 548 Twall [inches]: 8.625 Fluence [1019 Region/Component Cu Ni P Mn Un-Irradiated

1. Material Neutron/cm2, Description [wt%] [wt%] [wt%] [wt%] RTNDT(u) [°F]

E>1 MeV]

1 Low. Shell Axial Weld Linde 0091 .240 .160 .014 1.630 -80 7.22 2 Low. Shell Axial Weld Linde 0091 .240 .160 .014 1.630 -80 7.22 3 Low. Shell Axial Weld Linde 0091 .240 .160 .014 1.630 -80 7.22 4 Int. Shell Axial Weld Linde 124 .160 .100 .012 1.630 -56 7.22 5 Int. Shell Axial Weld Linde 124 .160 .100 .012 1.630 -56 7.22 6 Int. Shell Axial Weld Linde 124 .160 .100 .012 1.630 -56 7.22 7 Int./Low. Circ Weld Linde 0091 .210 .060 .014 1.630 -60 7.22 8 Lower Shell Plate A 533B .150 .600 .005 1.45 -8 7.22 9 Lower Shell Plate A 533B .140 .660 .005 1.45 20 7.22 10 Lower Shell Plate A 533B .110 .740 .006 1.45 -16 7.22 11 Inter. Shell Plate A 533B .150 .560 .006 1.45 10 7.22 12 Inter. Shell Plate A 533B .140 .550 .005 1.45 5 7.22 13 Inter. Shell Plate A 533B .110 .560 .007 1.45 10 7.22 3

ATTACHMENT (1)

PROPOSED ALTERNATIVE ISI-020 Table 3. Details of TWCF Calculation at 60 EFPY Outputs Methodology Used to Calculate T30: NUREG-1874 Controlling Material Fluence [1019 RTMAX-XX Region # Neutron/cm2, (flux) T30 [°F] TWCF95-XX

[R]

(From E>1 MeV]

Above)

Axial Weld - AW 9 639.17 7.22 3.81E+10 159.48 8.45E-11 Circumferential Weld - CW 9 639.17 7.22 3.81E+10 159.48 1.63E-16 Plate - PL 9 639.17 7.22 3.81E+10 159.48 3.50E-11 TWCF95-TOTAL (AWTWCF95-AW + PLTWCF95-PL + CWTWCF95-CW) 2.89E-10 As indicated in Table 2, there are four flaws in the beltline region of the reactor vessel. Three of these flaws meet the Allowable Number of Flaws criteria in SECY-07-0104. However, one flaw, with a through wall extent of 0.60 inches exceeds the criteria. The location of all four flaws relative to the beltline materials is illustrated in Figure 1. The circled numbers in Figure 1 correspond to the regions in Table 3. While one flaw is outside the limits in SECY-07-0104 it is not expected that this flaw would increase the Calvert Cliffs Unit 2 TWCF value above that of the pilot plant for the following reasons:

• This plate which the flaw is located in has a maximum RTNDT + T30 of 141.74°F and is not the limiting material in the beltline region. Furthermore, the peak fluence occurs at the 10, 80, 100, 170, 190, 260, 280, and 350 degree positions and was used to calculate the T30 shift for this plate.

The fluence at the 30 degree position where longitudinal weld 2-203A is located in less than 60% of that of the peak fluence. Therefore, the actual RTNDT + T30 at the specific location of this flaw is less than 141.74°F

• The total number of flaws detected in the Calvert Cliffs Unit 2 beltline is far less than that allowed in Tables 2 and 3 of SECY-07-0104.

• The TWCF for the Calvert Cliffs Unit 2 reactor vessel is more than 3 orders of magnitude below that for the bounding pilot plant vessel in WCAP-16168-NP-A, Revision 2.

Duration of Proposed Alternative This proposed alternative is applicable to the Calvert Cliffs Unit 2 ISI program for the remainder of the renewed licensed lifetime of the RPV for the examination categories B-A and B-D welds.

References

1. ASME Boiler and Pressure Vessel Code,Section XI, 1998 Edition, with no Addenda

2. OG-06-356, Plan for Plant Specific Implementation of Extended Inservice Inspection Interval per WCAP-16168-NP, Revision 1, Risk-Informed Extension of the Reactor Vessel In-Service Inspection Interval. MUHP 5097-99, Task 2059, October 31, 2006

3. NRC Regulatory Guide 1.174, Revision 1, An Approach for Using Probabilistic Risk Assessment in Risk-Informed Decisions on Plant-Specific Changes to the Licensing Basis, November 2002

4. WCAP-16168-NP-A, Revision 2, Risk-Informed Extension of Reactor Vessel In-Service Inspection Interval, June 2008 4

ATTACHMENT (1)

PROPOSED ALTERNATIVE ISI-020

5. NUREG-1874, Recommended Screening Limits for Pressurized Thermal Shock," March, 2007

6. NRC Letter Report, Generalization of Plant-Specific Pressurized Thermal Shock (PTS) Risk Results to Additional Plants, December 14, 2004

7. NRC Regulatory Guide 1.150, Revision 1, Ultrasonic Testing of Reactor Vessel Welds During Preservice. and Inservice Examinations, February 1983

8. S. Bajwa (NRC) to C. H. Cruse (CCNPP), Relief request from the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code) requirements to use Performance Demonstration Initiative Program - Reactor Pressure Second Ten-Year Inservice Inspection Interval - Calvert Cliffs Nuclear Power Plant Unit Nos. 1 and 2 (TAC Nos. M99819 and M99820, January 5, 1998

9. SECY-07-0104, Proposed Rulemaking - Alternate Fracture Toughness Requirements for Protection against Pressurized Thermal Shock, Enclosure 1, June 25, 2007 (ADAMS Accession Number ML070570141) 5

ATTACHMENT (1)

PROPOSED ALTERNATIVE ISI-020 Figure 1: Calvert Cliffs Unit 2 Beltline Flaw Map 6

ATTACHMENT (2)

PROPOSED ALTERNATIVE ISI-021 Calvert Cliffs Nuclear Power Plant, Inc.

October 1, 2008

ATTACHMENT (2)

PROPOSED ALTERNATIVE ISI-021 American Society of Mechanical Engineers (ASME) Code Component(s) Affected The affected component is the Calvert Cliffs Nuclear Power Plant (CCNPP) Unit 2 reactor pressure vessel (RPV), specifically the following ASME Boiler and Pressure Vessel (BPV) Code Section XI (Reference 1) examination categories and item numbers covering examinations of the RPV. These examination categories and item numbers are from IWB-2500 and Table IWB-2500-1 of the ASME BPV, Code Section XI.

Examination Category Item No. Description B-N-2 B13.50 Interior Attachments Within Beltline Region B-N-2 B13.60 Interior Attachments Beyond Beltline Region B-N-3 B13.70 Core Support Structure (Throughout this request the above examination categories are referred to as the subject examinations and the ASME BPV Code Section XI is referred to as the Code.)

Applicable Code Edition and Addenda

American Society of Mechanical Engineers Code Section XI, Rules and Inservice Inspection of Nuclear Power Plant Components, 1998 Edition (no Addenda).

Applicable Code Requirement

In accordance with IWA-2430(d)(1), each inspection interval may be reduced or extended by as much as one year. Adjustments shall not cause successive intervals to be altered more than one year from the original pattern of intervals.

Additionally, Table IWB-2500-1, examination categories B-N-2 and B-N-3, item numbers B13.50, B13.60, and B13.70 requires a visual examination of the accessible interior attachment welds within and beyond the beltline region and a visual examination of the accessible core support structure surfaces of the RPV once each ten-year interval. The CCNPP Unit 2 Third Ten-Year Inservice Inspection (ISI) interval is scheduled to end June 30, 2009.

Reason for Request

In Westinghouse Topical Report WCAP-16168-NP-A, Revision 2 (Reference 2), the Pressurized Water Reactor Owners Group provided the technical and regulatory basis for decreasing the frequency of inspections by extending the ASME Code Section XI ISI interval from the current 10 years to 20 years for ASME Code Section XI examination categories B-A and B-D RPV welds. The Nuclear Regulatory Commission approved the topical report by letter dated May 8, 2008 (Reference 3). To implement the change presented in Reference 2, we are submitting Attachment (1) (ISI-20), in accordance with the Safety Evaluation (Reference 3) to request an alternative from the Code requirements pursuant to 10 CFR 50.55a(a)(3)(i) on the basis that the alternative inspection interval (20 years) provides an acceptable level of quality and safety. In Attachment (1) we identified 2019 and 2039 as the years in which future inspections of the examination categories B-A and B-D RPV welds will be performed. The intent of this relief request (ISI-21) is to allow deferral of the subject examinations to the same time (2019 and 2039 refueling outages) as the examination categories B-A and B-D RPV welds described in Attachment (1).

During the ten-year ISI of the RPV shell, lower head, and nozzle welds in 1999, CCNPP also performed visual examinations of the RPV interior attachments and the core support structure. Since the core support structure (called a core barrel on Combustion Engineering designed plants) requires removal to 1

ATTACHMENT (2)

PROPOSED ALTERNATIVE ISI-021 facilitate examination of the RPV shell, lower head, and nozzle welds, the visual examinations of ASME examination categories B-N-2 and B-N-3 have historically been performed during the same outage at the end of the ISI interval.

Calvert Cliffs Nuclear Power Plant has also committed to the development and implementation of a plant specific Reactor Vessel Internals (RVI) inspection program and subsequent submittal to the Nuclear Regulatory Commission two years prior to the period of extended operation. Calvert Cliffs Nuclear Power Plant may elect to perform the enhanced examinations for the RVI inspection program coincident with the core barrel removal in 2019. To complete the full scope of the RVI examination it is expected to require a complete core offload and removal of all internals to facilitate implementation of the examinations. Portions of the RVI inspection may be performed prior to this time as may be prescribed in that program.

Performing all core barrel removed related examinations during the same refueling outage will result in significant savings in dose and outage duration since the same equipment and personnel used for visual and volumetric examination of the RPV shell welds and nozzle welds from the RPV interior can be used to implement the required RVI examinations. Additionally, removing the RPV internals only once to accommodate all the examinations discussed in this relief request would result in significant savings in radiation exposure.

Proposed Alternative and Basis for Use The third ten-year ISI interval for CCNPP began on July 1, 1999 and is scheduled to conclude on June 30, 2009. With the allowed one-year extension of IWA-2430(d)(1), the interval may be extended to June 30, 2010.

Calvert Cliffs Nuclear Power Plant proposes to perform the subject examinations for the third ten-year ISI interval on or before June 30, 2019. The subject examinations are currently scheduled to be performed during the spring 2009 refueling outage. The proposed alternative inspection would enable the subject examinations to be performed during the 2019 refueling outage and the 2039 refueling outage with the risk-informed extension of the RV ISI. In accordance with 10 CFR 50.55a(a)(3)(ii), this interval extension is requested on the basis that performing the examination of the RPV interior attachments and core support structure separate in time from the RPV shell, head, and nozzle welds would result in hardship or unusual difficulty without a compensating increase in quality or safety.

The full scope examination required by ASME examination categories B-N-2 and B-N-3 requires the removal of all the fuel and the core barrel from the RPV. An unnecessary risk is created by removal of the core barrel to perform a visual examination without a compensating increase in quality or safety.

Further, the radiation exposure to establish the conditions for and perform the ASME examination categories B-N-2 and B-N-3 examinations would essentially double if the subject examinations were performed separate in time from the RPV shell, lower head, and nozzle weld examinations.

The visual examinations of the RPV interior attachments and the core support structure have been performed several times at CCNPP with no relevant indications noted during the examinations. The examinations were last performed during the 1999 refueling outage with acceptable results. Additionally, review of industry surveys indicate that these examinations have been performed many times by the industry without any significant findings relevant to the Calvert Cliffs reactor vessel design.

As stated in Reference 2, it must be recognized that all reactor coolant pressure boundary failures occurring to date have been identified as a result of leakage, and were discovered by visual examination.

The proposed RV ISI interval extension does not alter the visual examination interval. The reactor vessel 2

ATTACHMENT (2)

PROPOSED ALTERNATIVE ISI-021 would undergo, as a minimum, the Section XI Examination Category B-P pressure tests and visual examinations conducted at the end of each refueling before plant start-up, as well as leak tests with visual examinations that precede each start-up following maintenance or repair activities. The minimum visual examinations discussed in Reference 2 are not the subject examinations (i.e., B-N-2 and B-N-3) of this relief request. During the 2009 refueling outage, CCNPP will be performing the ASME examination category B-N-1 visual examination. This examination will include the space that is made accessible for examination by the removal of components during normal refueling outages. This examination is required once each period and will provide reasonable assurance of structural integrity. As discussed further in Reference 2, defenses against human errors are preserved with the increase in inspection interval. Specifically, the increase in the inspection interval reduces the frequency for which the RV lower internals need to be removed thereby reducing the possibility for human error and damage to the core.

Therefore, in accordance with 10 CFR 50.55a(a)(3)(ii), this interval change from 10 to 20 years for the subject examinations is requested on the basis that compliance with the specified requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.

Duration of Proposed Alternative This proposed alternative is applicable to the third and fourth ten-year ISI for the examination categories B-N-2 and B-N-3, Item Numbers B13.50, B13.60, and B13.70 visual examinations.

References

1. ASME Boiler and Pressure Vessel Code,Section XI, 1998 Edition with no Addenda

2. WCAP-16168-NP-A, Revision 2, Risk-Informed Extension of Reactor Vessel In-Service Inspection Interval, June 2008

3. Final Safety Evaluation For Pressurized Water Reactor Owners Group (PWROG) Topical Report (TR) WCAP-16168-NP, Revision 2, Risk-Informed Extension Of The Reactor Vessel In-Service Inspection Interval (TAC No. MC9768), Dated May 8, 2008 3