ML15051A368
| ML15051A368 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 02/16/2015 |
| From: | Mark D. Sartain Virginia Electric & Power Co (VEPCO) |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 15-022 | |
| Download: ML15051A368 (6) | |
Text
VIRGINIA ELECTRIC AND POWER COMPANY RICHMOND, VIRGINIA 23261 February 16, 2015 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555-0001 Serial No.:
NAPS/ETS:
Docket Nos.:
License Nos.:
10 CFR 50.90 15-022 RO 50-338/339 NPF-4/7 VIRGINIA ELECTRIC AND POWER COMPANY NORTH ANNA POWER STATION UNITS 1 AND 2 RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION PROPOSED LICENSE AMENDMENT REQUEST CLARIFICATION OF REACTOR COOLANT SYSTEM HEATUP AND COOLDOWN TECHNICAL SPECIFICATION FIGURES In a letter dated August 27, 2014 (Serial No.14-424), Virginia Electric and Power Company (Dominion) submitted a license amendment request to revise the North Anna Power Station Units I and 2 Technical Specifications (TS). TS Figures 3.4.3-1 and 3.4.3-2, North Anna Units 1 and 2 Reactor Coolant System Heatup Limitations and North Anna Units 1 and 2 Reactor Coolant System Cooldown Limitations, respectively, are being revised for clarification and to be fully representative of the allowable operating conditions during Reactor Coolant System (RCS) startup and cooldown evolutions. Specifically, the revisions to TS Figures 3.4.3-1 and 3.4.3-2 are the extension of the temperature axes to reflect temperatures up to RCS full power operation, the extension of the pressure axes to less than 0 psig to bound RCS conditions to support vacuum-assist fill of the RCS loops, and the addition of information regarding the reactor boltup temperature.
Associated TS 3.4.3 Bases changes were provided for information.
In a January 14, 2015 e-mail from Dr. V. Sreenivas, the NRC requested additional information (RAI) to complete the review of the proposed amendment. The attachment to this letter contains Dominion's response to the RAI.
Should you have any questions or require additional information, please contact Mr. Jay Leberstien at (540) 894-2574.
Respectfully, Mark D. Sartain Vice President - Nuclear Engineering COMMONWEALTH OF VIRGINIA )
I Vicki L. Null NOTARY PUBLIC Commonwealth of Virginia Reg. # 140542 MyComission Expires May 31, 2018I i
I COUNTY OF HENRICO
)
The foregoing document was acknowledged before me, in and for the County and Commonwealth aforesaid, today by Mr. Mark D. Sartain, who is Vice President - Nuclear Engineering, of Virginia Electric and Power Company. He has affirmed before me that he is duly authorized to execute and file the foregoing document in behalf of that company, and that the statements in the document are true to the best of his knowledge and belief.
Acknowledged before me this &.-day of-2015.
My Commission Expires: L4
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Notary Public
Serial No.15-022 Docket Nos. 50-338/339 Page 2 of 2 Commitments contained in this letter:
- 1. If the revision of the fluence model indicates the neutron fluence exposure of the inlet and outlet nozzles would be greater than lx1017 n/cm 2 (E > 1 MeV) at the end of the licensed operating period, Dominion will advise the NRC accordingly and provide a schedule for submittal of revised P-T limit curves for North Anna Units 1 and 2, if necessary.
Attachment
- 1. Response to Request for Additional Information cc:
U.S. Nuclear Regulatory Commission - Region II Marquis One Tower 245 Peachtree Center Avenue, NE Suite 1200 Atlanta, GA 30303-1257 State Health Commissioner Virginia Department of Health James Madison Building - 7 th floor 109 Governor Street Suite 730 Richmond, VA 23219 Dr. V. Sreenivas NRC Project Manager-North Anna U.S. Nuclear Regulatory Commission One White Flint North Mail Stop 08 G-9A 11555 Rockville Pike Rockville, MD 20852-2738 Ms. Karen Cotton-Gross NRC Project Manager - North Anna U.S. Nuclear Regulatory Commission One White Flint North Mail Stop 08 G-9A 11555 Rockville Pike Rockville, MD 20852-2738 NRC Senior Resident Inspector North Anna Power Station
Serial No.15-022 Docket Nos. 50-338/339 Attachment Response to Request for Additional Information Virginia Electric and Power Company (Dominion)
North Anna Power Station Units I and 2
Serial No.15-022 Docket Nos. 50-338/339 Page 1 of 3 REQUEST FOR ADDITIONAL INFORMATION PROPOSED CHANGES TO NORTH ANNA POWER STATION UNITS I AND 2 REGARDING CLARIFICATION OF REACTOR COOLANT SYSTEM HEATUP AND COOLDOWN TECHNICAL SPECIFICATION FIGURES NORTH ANNA POWER STATION. UNITS 1 AND 2 By letter dated August 27, 2014, Virginia Electric Power Company (Dominion, the licensee) provided a proposed license amendment request, "Clarification of Reactor Coolant System Heatup and Cooldown Technical Specification Figures" (Agencywide Documents Access and Management System (ADAMS)
Accession Number ML14246A190). The licensee submitted a request for changes to the North Anna Power Station (North Anna) Units 1 and 2 Technical Specifications pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.90. The proposed amendment would revise Figures 3.4.3-1, "Reactor Coolant System Heatup Limitations" and 3.4.3-2, "Reactor Coolant System Cooldown Limitations," to address vacuum fill operations.
RAI 1
BACKGROUND 10 CFR Part 50, Appendix G requires that pressure-temperature (P-T) limits be developed to bound all ferritic materials in the reactor vessel (RV). Further, Sections I and IV.A of 10 CFR, Part 50, Appendix G specify that all ferritic reactor coolant pressure boundary (RCPB) components outside of the RV must meet the applicable requirements of American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),
Section
- III, "Rules for Construction of Nuclear Facility Components."
ISSUE As clarified in Regulatory Information Summary (RIS) 2014-11, Information on Licensing Applications for Fracture Toughness Requirements for Ferritic Reactor Coolant Pressure Boundary Components (ADAMS Accession No. ML14149A165), P-T limit calculations for ferritic RV components other than those materials with the highest reference temperature, may define curves that are more limiting than those calculated for the RV beltline shell materials because the consideration of stress levels from structural discontinuities (such as nozzles) may produce a lower allowable pressure.
REQUEST Describe how the P-T limit curves for North Anna Units 1 and 2 consider all ferritic pressure boundary components of the reactor vessel that are predicted to experience a neutron fluence exposure greater than lx10 7 n/cm 2 (E > 1 MeV) at the end of the licensed operating period.
Serial No.15-022 Docket Nos. 50-338/339 Page 2 of 3 If the current P-T limit curves do not consider all ferritic pressure boundary components of the reactor vessel that are predicted to experience a neutron fluence exposure greater than 1x10 17 n/cm 2 (E > 1 MeV) at the end of the licensed operating period, provide appropriately revised P-T limit curves to the NRC for review.
Dominion Response The existing P-T limits curves for North Anna Units 1 and 2 are based upon the ferritic pressure boundary materials from the reactor flange, as well as those materials classified as the traditional beltline materials immediately surrounding the reactor vessel core.
The existing fluence projections are based upon the NRC approved fluence methodology (99-242) described in VEP-NAF-3, Reactor Vessel Fluence Analysis Methodology as applied in WCAP-15112 R1, North Anna Units 1 and 2 WOG Reactor Vessel 60-Year Evaluation Minigroup Heatup and Cooldown Limit Curves for Normal Operation. These fluence calculations were performed with a methodology consistent with the requirements of NRC Regulatory Guide (RG) 1.190, Calculational and Dosimetry Methods for Determining Pressure Vessel Neutron Fluence.
At the time the P-T limits curves for North Anna Units 1 and 2 were developed, the fluence model used to project neutron fluence exposure was limited to the ferritic pressure boundary materials immediately adjacent to the reactor core. The geometry of the core consists of vertical baffles of different widths such that the reactor is octant symmetric. The axial extent of the current model extends from approximately 1-foot below the active fuel to approximately 16.6 inches above the active fuel. The inlet and outlet nozzles are located outside the axial extent of the current fluence model. The fluence around the circumference of the reactor vessel varies from a minimum value to a maximum value corresponding to the core geometry and symmetry. Neutron fluence projections are typically determined at various azimuthal locations to ensure the maximum calculated neutron fluence.
To ensure the P-T limits curves are bounding, the maximum calculated fluence values for each of the traditional beltline materials have been determined at various azimuthal locations around the reactor vessel and combined with the initial material properties and margins to identify the most limiting adjusted material properties. The resulting limiting material properties have been used in combination with stress intensity formulas for a postulated 1/4T and 3/4T flaw to produce conservative P-T limits curves for North Anna Units 1 and 2. Details of the methodology used to produce the P-T limits curves for North Anna Units 1 and 2 are outlined in WCAP-14040-A, Methodology Used to Develop Cold Overpressure Mitigating System Setpoints and RCS Heatup and Cooldown Limit Curves.
Since the fluence model is limited to approximately 1-foot below the active fuel to approximately 16.6 inches above the active fuel, and the inlet and outlet nozzles are located outside this region, the precise position of a demarcation line around the
A Serial No.15-022 Docket Nos. 50-338/339 Page 3 of 3 circumference of the reactor vessel for a neutron fluence threshold of 1 x 1017 n/cm 2 (E
> 1 MeV) has not been determined to date.
When the P-T limits curves were constructed, the maximum fluence projections typically determined at incremental azimuthal locations were used to produce the various adjusted reference temperatures for the materials adjacent to the core. However, the existing P-T limits curves did not use adjusted reference temperature values for the inlet and outlet nozzles because the fluence projections are beyond the limits of the model and are thought to have neutron fluence exposures less than 1 x 1017 n/cm 2 (E > 1 MeV).
Upon receipt of the NRC RAI, Dominion initiated discussions with Westinghouse to determine a schedule for amending the axial extent of the fluence model to encompass the reactor vessel inlet and outlet nozzles. Westinghouse indicated they can complete the requested revision of the fluence model by August 31, 2015. Following completion of the fluence model revision, Dominion will be able to validate whether the inlet and outlet nozzles will have a neutron fluence of less than lx1017 n/cm 2 (E > 1 MeV) at the end of the licensed operating period.
The existing P-T limits curves for North Anna Units 1 and 2 are considered conservative based upon information available at the time the fluence values were determined, since maximum fluence values have been combined with material properties representing the traditional beltline region in a manner that produces limiting adjusted material properties. Based on available information from the existing fluence model, the position of the active region of the core, and the location of the inlet and outlet nozzles, it is expected that revision of the fluence model will confirm that neutron fluence exposure of the inlet and outlet nozzles is less than lx1017 n/cm 2 (E > 1 MeV) at the end of the licensed operating period. Once the fluence model is revised, and the inlet and outlet nozzles are confirmed to have less than lx1017 n/cm 2 (E > 1 MeV), it can be concluded that ferritic pressure boundary components of the reactor vessel that are predicted to experience a neutron fluence exposure greater than 1 x10 17 n/cm 2 (E > 1 MeV) at the end of the licensed operating period have been used to derive the existing P-T limits curves for North Anna Units 1 and 2.
Although not expected, should the revision of the fluence model indicate the neutron fluence exposure of the inlet and outlet nozzles would be greater than 1x10 17 n/cm 2 (E > 1 MeV) at the end of the licensed operating period, Dominion will advise the NRC accordingly and provide a schedule for submittal of revised TS P-T limits curves for North Anna Units 1 and 2, if necessary.