ML12138A135
| ML12138A135 | |
| Person / Time | |
|---|---|
| Site: | Nine Mile Point  |
| Issue date: | 05/07/2012 |
| From: | Swift P Constellation Energy Nuclear Group |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| Download: ML12138A135 (13) | |
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P.O. Box 63 Lycoming, NY 13093 NINE MILE POINT NUCLEAR STATION May 7, 2012 U.S. Nuclear Regulatory Commission Washington, DC 20555-0001 ATTENTION:
SUBJECT:
Document Control Desk Nine Mile Point Nuclear Station Unit No. 1; Docket No. 50-220 Reactor Pressure Vessel Head Weld Flaw Evaluation - Response to NRC Request for Additional Information
REFERENCE:
(a) Letter from P. M. Swift (NMPNS) to Document Control Desk (NRC), dated June 28, 2011, Reactor Pressure Vessel Head Weld Flaw Evaluation Nine Mile Point Nuclear Station, LLC (NMPNS) hereby transmits supplemental information requested by the NRC in support of a previously submitted structural evaluation of a subsurface flaw indication found in a Nine Mile Point Unit 1 reactor pressure vessel (RPV) closure head weld during the 2011 refueling outage. The structural flaw evaluation (Reference a) was submitted for NRC staff review and approval in accordance with the requirements of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code,Section XI, Subsection IWB-3610 (2004 Edition). The supplemental information, provided in Attachments 1 and 2 to this letter, responds to the NRC request for additional information that was transmitted to NMPNS in an NRC email dated April 5, 2012.
This letter contains no new regulatory commitments. Should you have any questions regarding the information in this submittal, please contact John J. Dosa, Director Licensing, at (315) 349-5219.
Very truly yours, NL}%4 Paul M. Swift Manager Engineering Services
- 4700L
Document Control Desk May 7, 2012 Page 2 PMS/DEV Attachments:
- 1. Nine Mile Point Unit 1 - Response to NRC Request for Additional Information Regarding Reactor Pressure Vessel Head Weld Flaw Evaluation
- 2. Nine Mile Point Unit 1 -
Supplemental Information for Calculation SOVESSELM035 (SIA File No. 1100566.301), Reactor Pressure Vessel Head Flaw Evaluation cc:
Regional Administrator, Region I, NRC Project Manager, NRC Resident Inspector, NRC
ATTACHMENT 1 NINE MILE POINT UNIT 1 RESPONSE TO NRC REQUEST FOR ADDITIONAL INFORMATION REGARDING REACTOR PRESSURE VESSEL HEAD WELD FLAW EVALUATION Nine Mile Point Nuclear Station, LLC May 7, 2012
ATTACHMENT 1 NINE MILE POINT UNIT 1 RESPONSE TO NRC REQUEST FOR ADDITIONAL INFORMATION REGARDING REACTOR PRESSURE VESSEL HEAD WELD FLAW EVALUATION By letter dated June 28, 2011, Nine Mile Point Nuclear Station, LLC (NMPNS) submitted a structural evaluation of a subsurface flaw indication found in a Nine Mile Point Unit 1 (NMP1) reactor pressure vessel (RPV) closure head weld during the 2011 refueling outage. The structural flaw evaluation was submitted for NRC staff review and approval in accordance with the requirements of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code,Section XI, Subsection IWB-3610 (2004 Edition). This attachment provides supplemental information in response to the NRC request for additional information that was transmitted to NMPNS in an NRC email dated April 5, 2012. The NRC request is repeated (in italics), followed by the NMPNS response.
Request Section 63,2 includes a fatigue crack growth analysis. The actual applied stress intensity Kfor the large indication in the RPV head weld is assumed to be less than a stress intensity factor K of 63.25 ksi-inW based on the nominal safety factor with the minimum fracture toughness of the material.
Justify the assumed stress intensity factor K of 63.25 ksi-inA by calculating the maximum applied Kfor the large indication in the RPV head weld under normal operating conditions. Include a reference for the formula used to calculate the applied K
Response
The applied stress intensity factor (K) has been calculated by modeling the indication as a semi-elliptical subsurface crack in a plate. This model is from the ASME Code (2004 Edition),Section XI, Appendix A.
The results of this calculation, provided in Attachment 2, demonstrate that the applied stress intensity factor is much less than the value of 63.25 ksi-in"' that was used in the crack growth analysis provided in the June 28, 2011 NMPNS letter. Therefore, the analysis provided in the June 28, 2011 NMPNS letter is conservative.
I of I
ATTACHMENT 2 NINE MILE POINT UNIT 1 SUPPLEMENTAL INFORMATION FOR CALCULATION SOVESSELM035 (SIA FILE NO. 1100566.301)
REACTOR PRESSURE VESSEL HEAD FLAW EVALUATION Nine Mile Point Nuclear Station, LLC May 7, 2012
Structural Integrity Associates, Inc.
Response to RAI on Calculation Package 1100566.301 Issue:
Section 6.3.2 includes a fatigue crack growth analysis. The actual applied stress intensity K for the large indication in the RPV head weld is assumed to be less than a stress intensity factor K of 63.25 ksi-Vin based on the nominal safety factor with the minimum fracture toughness of the material.
Request:
Justify the assumed stress intensity factor K of 63.25 ksi-v'in by calculating the maximum applied K for the large indication in the RPV head weld under normal operating conditions.
Include a reference for the formula used to calculate the applied K.
SI Response:
In Calculation Package 1100566.301 [1], the indication in the reactor pressure vessel closure head was reported with the following dimensions:
Wall thickness at the indication, t:
5.4783 inches Closure head radius:
106.5016 inches Indication depth, 2a:
1.2319 inches Indication length, 1:
79 inches A crack model of semi-elliptical subsurface crack in a plate, shown in Figure 1, is used to calculate the stress intensity factor for the indication. This model is from ASME Boiler and Pressure Vessel Code, Section Xl, Appendix A [2]. As stated in A-3100 of Reference 2, the solutions for K, are based on flat plate geometry and can be used for subsurface flaws in cylinders for all values of R/t (the ratio of mean radius to thickness).
Per Appendix A, the stress intensity factors for subsurface flaws shall be calculated using the membrane and bending stresses at the flaw location by the following equation.
KI
[,mM, +crbMb (1) where a=
membrane stress Response to RAI on Calculation Package 1100566.301 Page 1 of 8
Structural Integrity Associates, Inc.
Ub = bending stress a
= half of the minor axis of the elliptical flaw Mm= correction factor for membrane stress from Figure 2 Mb = correction factor for bending stress from Figure 3 Q = flaw shape parameter I,
t65 Q = 1 + 4.593(/1
-qy (2) 1
= the major axis of the flaw a/I = flaw aspect ratio 0*a/l<0.5 qy = plastic zone correction factor calculated using the following equation q, =k[('mMm +O'bMb)/O'yo/6 (3) cy= material yield strength The axial stresses in the closure head are presented in Table 1 of Reference 1 for the load cases of pressure, boltup, heatup, cooldown and emergency blowdown transients. These through-wall stress distributions are linearly curve-fitted to obtain the membrane and bending stresses.
The stress intensity factors as shown in Equation 1 are calculated using Structural Integrity Associates' software pc-CRACK" [3] for a crack aspect ratio of a/I =(1.2319/2)/79=0.0078.
The stress intensity factors for individual load cases are presented in Figure 4. It shows that the stress intensity factor, K1, from the pressure load case is the highest while the heatup load case yields the lowest K1. Based on the distributions, it can be seen that the load combination of pressure + bolt up + emergency blowdown yields the highest K1. The total stress intensity factor from this load combination is shown in Figure 5. Also, the allowable fracture toughness, Kic, of 63.25 ksi-Vin is shown in Figure 5. It is shown that, only beyond a crack depth 2a of 3.4 inches (half crack depth a = 1.7 inches), the total stress intensity factor would exceed the material fracture toughness of 63.25 ksi--Vin. For the current reported indication of half crack depth at 0.616 inch, the applied stress intensity factor is about 20.39 ksi-Vfin. This applied stress intensity factor is much less than the 63.25 ksi-V/in used in the crack growth analysis in the Reference 1 calculation package.
Response to RAI on Calculation Package 1100566.301 Page 2 of 8 Response to RAI on Calculation Package 1100566.301 Page 2 of 8
V Structural Integrity Associates, Inc.
References:
- 1. SI Calculation 1100566.301, 'Reactor Pressure Vessel Head Flaw Evaluation,' Rev. 0.
- 2. ASME Boiler & Pressure Code,Section XI, Appendix A, 2004 Edition
- 3. pc-CRACK', Version 4.0.1.0, Structural Integrity Associates, December 2011.
Prepared by:
Verified by:
04/20/2012 Date David G. Dijamco Consultant 04/20/2012 Date S. S. (Stan) Tang Associate Approved by:
G. Angah Miessi Associate 04/20/2012 Date Response to RAI on Calculation Package 1100566.301 Page 3 of 8 Response to RAI on Calculation Package 1100566.301 Page 3 of 8
V Structural Integrity Associates, Inc.
Figure 1: Elliptical Subsurface Crack in a Plate Response to RAI on Calculation Package 1100566.301 Page 4 of 8 Response to RAI on Calculation Package 1100566.301 Page 4 of 8
v Structural Integrity Associates, Inc.
1.8 1.5 PoitT f Point 2
N IL C0p I
I 1.4 1.3 1.2 1.1 1.0 0
0.1 0.2 0.3 0.4 0.5 0.6 Flaw Eccentricity Ratio 2L.
point Point 2 I
I wall hicknessa eccentricity ouaw extreme of the minor diameter of.114m (closer to surface)
Inner extreme of the minor dawm of atllpst (further from surfae)}
FIG. A-3310-1 MEMBRANE STRESS CORRECTION FACTOR FOR SUBSURFACE FLAWS Figure 2: Membrane Stress Correction Factor for Subsurface Flaws Response to RAI on Calculation Package 1100566.301 Page 5 of 8
V Structural Integrity Associates, inc.
1.0 0.9 OR 0.7 OR 0.5 OA 0.3 0.2 0.1 0.0 Neutral axis Tension 5fda Comprssion side jIaIa
-0.2
-0.3
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GENERAL NOTE:
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If the flew center line is on the corn.
prtesive side of the neuttral axis.
the
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0.1 0.2 03 0.4 0.5 0.5
-0.7 Flew Eengltri*tly Ratio 2PA FIG. A-3310-2 SENDING STRESS CORRECTION FACTOR FOR SUBSURFACE FLAWS (For Deinitlons of Nomenclature, See Fig. A-3310-1)
Figure 3: Bending Stress Correction Factor for Subsurface Flaws Response to RAI on Calculation Package 1100566.301 Page 6 of 8
Structural Integrity Associates, Inc.
35 30 25 20
'~15
.10 5
0
-5 0
0.2 0.4 0.6 0.8 1
1.2 1.4 1.6 1.8 2
Half Crack Depth (in)
Figure 4: Stress Intensity Factors Response to RAI on Calculation Package 1100566.301 Page 7 of 8 Response to RAI on Calculation Package 1100566.301 Page 7 of 8
V Structural Integrity Associates, Inc.
70 60 50 40 S30 20 10 0
0 0.2 0.4 0.6 0.8 1
1.2 1.4 1.6 1.8 2
Half Crack Depth (in)
Figure 5: Stress Intensity Factor, Load Combination Response to RAI on Calculation Package 1100566.301 Page 8 of 8