ML081050034
| ML081050034 | |
| Person / Time | |
|---|---|
| Site: | Nine Mile Point  |
| Issue date: | 04/02/2008 |
| From: | Laughlin G Constellation Energy Group |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| TAC MD6620 | |
| Download: ML081050034 (6) | |
Text
Constellation Energy Nine Mile Point Nuclear Station P.O. Box 63 Lycoming, NY 13093 April 2, 2008 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 Submittal of Additional Engineering Evaluations for Two Reactor Pressure Vessel Weld Flaws in Accordance with Amended License Renewal Application Commitment - Response to NRC Request for Additional Information (TAC No.
MD6620)
(a) Letter from G. J. Laughlin (NMPNS) to Document Control Desk (NRC), dated August 22, 2007, Submittal of Additional Engineering Evaluations for Two Reactor Pressure Vessel Weld Flaws in Accordance with Amended License Renewal Application Commitment
REFERENCES:
(b) Letter from M. J. David (NRC) to K. J. Polson (NMPNS), dated February 12, 2008, Request for Additional Information Regarding Nine Mile Point Nuclear Station, Unit No. 1, Additional Engineering Evaluation of Two Reactor Pressure Vessel Weld Flaws (TAC No. MD6620)
Nine Mile Point Nuclear Station, LLC (NMPNS) hereby transmits supplemental information requested by the NRC in support of previously submitted engineering evaluations of subsurface flaws in two Nine Mile Point Unit 1 reactor pressure vessel (RPV) welds. These engineering evaluations, included in the initial submittal dated August 22, 2007 (Reference a), considered additional fatigue growth and the additional irradiation embrittlement (for beltline materials) associated with operation for an additional 20 years, in accordance with an Amended License Renewal Application commitment. The supplemental information, provided in Attachment I to this letter, responds to the request for additional information (RAI) documented in the NRC's letter dated February 12, 2008 (Reference b).
This letter contains no new regulatory commitments.
.A/'ei7'
Document Control Desk April 2, 2008 Page 2 Should you have any questions regarding the information in this submittal, please contact T. F. Syrell, Licensing Director, at (315) 349-5219.
Very truly yours, 2Ga/Jay Laughlin Manager Engineering Services GJL/DEV
Attachment:
1.
Nine Mile Point Unit 1 - Response to NRC Request for Additional Information Regarding the Additional Engineering Evaluations for RPV Welds RV-WD-140 and RV-WD-099 for the License Renewal Period cc:
S. J. Collins, NRC R. V. Guzman, NRC Resident Inspector, NRC
ATTACHMENT 1 NINE MILE POINT UNIT 1 RESPONSE TO NRC REQUEST FOR ADDITIONAL INFORMATION REGARDING THE ADDITIONAL ENGINEERING EVALUATIONS FOR RPV WELDS RV-WD-140 AND RV-WD-099 FOR THE LICENSE RENEWAL PERIOD Nine Mile Point Nuclear Station, LLC April 2, 2008
ATTACHMENT 1 NINE MILE POINT UNIT 1 RESPONSE TO NRC REQUEST FOR ADDITIONAL INFORMATION REGARDING THE ADDITIONAL ENGINEERING EVALUATIONS FOR RPV WELDS RV-WD-140 AND RV-WD-099 FOR THE LICENSE RENEWAL PERIOD By letter dated August 22, 2007, Nine Mile Point Nuclear Station, LLC (NMPNS) submitted engineering evaluations of subsurface flaws in two Nine Mile Point Unit 1 (NMP1) reactor pressure vessel (RPV) welds. These engineering evaluations considered additional fatigue growth and the additional irradiation embrittlement (for beltline materials) associated with operation for an additional 20 years, in accordance with an Amended License Renewal Application commitment. This attachment provides supplemental information in response to the request for additional information documented in the NRC's letter dated February 12, 2008. Each individual NRC question is repeated (in italics), followed by the NMPNS response.
Question 1 Page 7 of 22 of Attachment (1) of your August 22, 2007, submittal states, "Note that any potential future increases in the leak test pressure are bounded by this evaluation since a higher leak test pressure will yield a higher temperature..." The technical basis is insufficient because the submitted flaw evaluation is bounding only when the increase offracture toughness due to a higher temperature exceeds the increase of applied stress intensity factor due to higher test pressure. Either delete this statement, or amend your
.basis for this statement if you can demonstrate that the increase of fracture toughness due to a higher temperature exceeds the increase of the applied stress intensity factor due to higher test pressure.
Response
NMPNS agrees that there is not adequate technical basis provided in Attachment (1) of our letter dated August 22, 2007 to support the statement cited in the question. Therefore, please disregard the subject statement. As noted on page 3 of 22 of Attachment (1), the impact on final allowable flaw sizes of future pressure-temperature curves developed for the license renewal period will be evaluated in accordance with the NMPNS design change control process.
Question 2 Figure 2 on Page 9 of 22 is supposed to show three curves of allowable flaw depth for flaw eccentricity ratios of -0.38, -0.22, and -0.20. However, it shows only one curve. Please confirm that the allowable flaw depth is insensitive toflaw eccentricity ratios such that the three curves become one.
Response
Please see the response to Question 3 below.
Question 3 Please explain why Figure 2 on Page 9 of 22 appears to show that the allowable flaw depth is insensitive to flaw eccentricity ratios while Figure 3 on Page 14 of 22 shows that the allowable flaw depth is sensitive to flaw eccentricity ratios. This serves as a check of the integrity of your computer program for flaw evaluation.
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ATTACHMENT 1 NINE MILE POINT UNIT 1 RESPONSE TO NRC REQUEST FOR ADDITIONAL INFORMATION REGARDING THE ADDITIONAL ENGINEERING EVALUATIONS FOR RPV WELDS RV-WD-140 AND RV-WD-099 FOR THE LICENSE RENEWAL PERIOD
Response
Figure 2 on page 9 of 22 of Attachment (1) of the NMPNS submittal dated August 22, 2007 is based on the use of Kia fracture toughness. The allowable flaw sizes computed for the three eccentricity ratios (a/L) of -0.38, -0.22, and -0.20 are actually computed to be smaller than the IWB-3500 Acceptance Criteria.
Since the IWB-3500 Acceptance Criteria are considered to represent the smallest range of acceptable flaw sizes, the computed allowable flaw sizes are set equal to the IWB-3500 Acceptance Criteria, and all four curves are plotted coincident with each other.
On the other hand, Figure 3 on page 14 of 22 of Attachment (1) uses K1c fracture toughness. For this case, the allowable flaw sizes computed for the three eccentricity ratios of -0.38, -0.22, and -0.20 are larger than the IWB-3500 Acceptance Criteria due to the increased material toughness. For this case, the allowable flaw sizes are not set equal to the IWB-3500 Acceptance Criteria, so they retain their calculated values and are depicted in the figure accordingly.
Question 4 Page 12 of 22 states, "Per Constellation input, the peak fluence for the upper plate from Reference [3],
as used in Table 3 and this revised analysis, is 2.33 times higher than the peak fluence for the Weld
@225. " Please provide relevant pages from Reference [3] showing the fluence map of the reactor pressure vessel beltline region and mark on the map the weld location at 2250.
Response
The ratio of 2.33 between the peak neutron fluence for the upper plate and the peak neutron fluence for weld RV-WD-140 at the 2250 location, referenced on page 12 of 22 of Attachment (1) to the NMPNS letter dated August 22, 2007, was a design input to the calculation of pressure-temperature operating limit curves for license renewal that was documented in Reference [3] of Attachment (1). The 2.33 value was established based on preliminary, conservative projections of the fluence for 46 effective full power years (EFPY) of operation that were available at the time that the Reference [3] analysis was originated in 2005. As shown in Table 4 on page 13 of 22 of Attachment (1), application of the 2.33 factor resulted in a peak fluence of 1.16E+18 n/cm 2 at the 225' location of weld RV-WD-140. This represents the maximum fluence anywhere along the length of weld RV-WD-140.
In 2006, updated neutron fluence calculations, performed in accordance with Regulatory Guide 1.190, were completed with more accurate projections through 46 EFPY of operation. For weld RV-WD-140 at the 225' location, a peak fluence of 1.OE+18 n/cm 2 was calculated (again representing the maximum fluence anywhere along the length of weld RV-WD-140). Since the fluence value used in the weld RV-WD-140 flaw evaluation (1.16E+ 18 n/cm2) is greater than the final calculated fluence value (1.OE+ 18 n/cm 2), the calculated flaw sizes at weld RV-WD-140 are conservative. This conclusion is documented on page 3 of 22 of Attachment (1).
The location and orientation of reactor vessel weld RV-WD-140 are shown on Figure 1.
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ATTACHMENT 1 NINE MILE POINT UNIT 1 RESPONSE TO NRC REQUEST FOR ADDITIONAL INFORMATION REGARDING THE ADDITIONAL ENGINEERING EVALUATIONS FOR RPV WELDS RV-WD-140 AND RV-WD-099 FOR THE LICENSE RENEWAL PERIOD 0"
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1.8637 INCHES PER DEGREE Figure 1: Nine Mile Point Unit 1 Reactor Vessel Rollout Drawing 3 of 3