ML14204A620
| ML14204A620 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 07/21/2014 |
| From: | Heacock D Dominion, Dominion Nuclear Connecticut |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 14-350 | |
| Download: ML14204A620 (9) | |
Text
Dominion Nuclear Connecticut, Inc. o 5000 Dominion Boulevard, Glen Alien, VA 23060 Web Address: www.dom.com July 21, 2014 U. S. Nuclear Regulatory Commission Serial No.14-350 Attention: Document Control Desk NSSL/MLC RO Washington, DC 20555 Docket No. 50-336 License No. DPR-65 DOMINION NUCLEAR CONNECTICUT. INC.
MILLSTONE POWER STATION UNIT 2 RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION REGARDING SEISMIC HAZARD AND SCREENING REPORT FOR SEISMIC RECOMMENDATION 2.1 By letter dated March 31, 2014, Dominion Nuclear Connecticut, Inc. (DNC) submitted the Response to March 12, 2012 Information Request Seismic Hazard and Screening Report for Recommendation 2.1 for Millstone Power Station (MPS) Units 2 (MPS2) and 3 (MPS3). In a letter dated July 16, 2014, the Nuclear Regulatory Commission transmitted a request for additional information (RAI) related to the submittal for MPS2. to this letter contains DNC's response to the RAI.
If you have any questions or require additional information, please contact Wanda Craft at (804) 273-4687.
Sincerely, David A. Heacock Chief Nuclear Officer Dominion Nuclear Connecticut, Inc...
I Commonweefth of VIMS 4 Reg. #140542 My Commission Expires May 31, 2016 COMMONWEALTH OF VIRGINIA
)
COUNTY OF HENRICO The foregoing document was acknowledged before me, in and for the County and Commonwealth aforesaid, today by David A. Heacock, who is Chief Nuclear Officer of Dominion Nuclear Connecticut, Inc.
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 yL=day of J, 2014.
My Commission Expires: 5- ".- .
No Notary u.oic
Serial No.14-350 Docket No. 50-336 Page 2 of 2 Commitments made in this letter: None Attachments:
- 1. Response to Request for Additional Information for the Response to March 12, 2012 Information Request Seismic Hazard and Screening Report for Recommendation 2.1 cc: U.S. Nuclear Regulatory Commission Region I 2100 Renaissance Blvd, Suite 100 King of Prussia, PA 19406-2713 Michael Balazik Project Manager U.S. Nuclear Regulatory Commission One White Flint North, Mail Stop 07 G13 11555 Rockville Pike Rockville, MD 20852-2738 Nicholas DiFrancesco Project Manager U.S. Nuclear Regulatory Commission One White Flint North, Mail Stop 08 D15 11555 Rockville Pike Rockville, MD 20852-2738 Juan Uribe Project Manager U.S. Nuclear Regulatory Commission One White Flint North, Mail Stop 11 F1 11555 Rockville Pike Rockville, MD 20852-2738 Mohan C. Thadani Senior Project Manager U.S. Nuclear Regulatory Commission One White Flint North, Mail Stop 08 B1 11555 Rockville Pike Rockville, MD 20852-2738 NRC Senior Resident Inspector Millstone Power Station
Serial No 14-350 Docket No. 50-336 Attachment I Response to Request for Additional Information for the Response to March 12, 2012 Information Request Seismic Hazard and Screening Report for Recommendation 2.1 Dominion Nuclear Connecticut, Inc.
Millstone Power Station Unit 2
Serial No 14-350 Docket No. 50-336 Attachment 1, Page 1 of 6 By letter dated March 31, 2014, Dominion Nuclear Connecticut, Inc. (DNC) submitted the Response to March 12, 2012 Information Request Seismic Hazard and Screening Report for Recommendation 2.1 for Millstone Power Station (MPS) Units 2 (MPS2) and 3 (MPS3).
In a letter dated July 16, 2014, the Nuclear Regulatory Commission transmitted a request for additional information (RAI) related to the submittal for MPS2. The response to the RAI is as follows:
Background
After reviewing Individual Plant Examination of External Events (IPEEE) Adequacy Evaluation and IPEEE High Confidence of a Low Probabilityof Failure (HCLPF)spectra (IHS) Development part of the Seismic Hazard and Screening Report for Millstone Power Station Unit 2 (MPS2), herein called Appendix B, and the earlier IPEEE submittal for MPS2, the NRC staff has two main requests for clarification as described below. The information on the clarificationswill be reviewed by the NRC staff as part of the NRC staff evaluation of the IPEEE adequacy and, if needed, to support a follow-on audit of the items addressedin the requests.
Request I As part of Appendix B, the licensee submitted a Peer-Review report which reviewed the HCLPFcapacity calculations used in the IPEEE Seismic Margin Analysis (SMA). Table 2 of the Peer-Review report lists 6 components for which the HCLPF peak ground acceleration(PGA) in the IPEEEreport for MPS2 is less than the plant HCLPF of 0.25g as shown in the table below (herein all HCLPFs are defined in terms of a 5-percent damping NUREG/CR-0098 rock spectral shape with the referred to PGA).
In agreement with the licensee submittal, Table 2 of the Peer-Review report describes how failure of three of those 6 structures, systems, and components (SSC) no longer affects the plant HCLPF and indicates that after a modification the revised HCLPF for another SSC increased to 0.29g. These components are the first four components in the table below.
The conclusion of the Peer-Review report is that once the licensee satisfactorilycompletes the actions listed in the notes column of the table below for the Battery Racks DB I and DB2 and for the Chilled Water Surge Tank, the plant level IPEEE HCLPF can be considered to be the NUREG/CR-0098 spectral shape (5-percent damping) anchored at
- 0. 25g PGA.
Serial No 14-350 Docket No. 50-336 Attachment 1, Page 2 of 6 SSC HCLPF SSC Table 3.2-3 S&A Notes IPEEE report Sheets 22S3-2-2 RSST Feeder Failure of enclosure no longer Breaker 0.19 0.19 affects the plant HCLPF (after a plant modification Block Wall 7.8 near 0.051 0.051 Failure does affect plant HCLPF Inverter 5 Inverter 5 Failure does affect plant HCLPF 120V AC Panel VR1 1 0.17 0.17 Failure does affect plant HCLPF and VR21 Dominion will locate an existing HCLPF calculation or Battery Racks DB1 and 0.13 0.13 reconstitute a calculation to DB2 (Battery 201A 201B) confirm that the HCLPF capacity is greater than 0.25g Dominion will locate an existing HCLPF calculation or Chilled Water Surge 0.22 0.136 reconstitute a calculation to Tank confirm that the HCLPF capacity is greater than 0.25g In Appendix B (Section B5.6, page B-24), the licensee states that subsequently to the Peer-Review report field walkdowns and evaluations were performed to reconstitute the HCLPF calculations for these two SSCs (Battery Racks DBI and DBI, and the Chilled Water Surge Tank). The conclusion in page B-24 of Appendix B is that the HCLPF capacity for each of these SSCs remains greater than or equal to the plant HCLPF capacity of 0.25g through modifications previously performed and/or evaluation of the as-built configuration. Appendix B refers to Dominion Engineering Technical Evaluation ETE-CEM-2014-0001 (Reference B7.27 of Appendix B) for the documentation of the evaluation of these two SSCs.
The new evaluations and related modifications result in an increase of the HCLPF for the two SSCs that are significant for the safety assessment, the Battery Racks DB I and DB 1, and the Chilled Water Surge Tank. However, these evaluations and modifications were not part of the IPEEE documentation previously reviewed by the NRC staff and were not part of the evaluations reviewed in the Peer-Review Report in Appendix B. To understand the details, scope and inputs for these new evaluations and related modifications for these two SSCs, the NRC staff requests:
- A detailed description of the methods and inputs for the new evaluations including how the new evaluations differed from the earlierevaluations for the MPS2 IPEEE,
Serial No 14-350 Docket No. 50-336 Attachment 1, Page 3 of 6 how the SSCs configurations changed from previously made modifications, and how the understanding of the as-built conditions changed from the earlier evaluations.
- A detailed description of the modifications to these SSCs, if any.
DNC Response For the MPS2 125V DC Main Station Battery Racks DB1 and DB2 and the Chilled Water Surge Tanks, the HCLPF evaluations were reconstituted and the HCLPF capacities for each of the components were demonstrated to be greater than or equal to the plant HCLPF capacity of 0.25g based on modifications previously performed and / or evaluation of the as-built configuration. The methods used in these two recent calculations are consistent with the guidance in the EPRI Seismic Margins Assessment Report NP-6041-SL, Revision 1 and the results of the analyses were independently verified. No new modifications were made to improve the HCLPF capacities of either the battery racks or the surge tank. Modifications to the DB1 and DB2 battery racks were made as a result of identified outliers discovered during resolution of Unresolved Safety Issue (USI) A-46. No new modifications, beyond those that were made and reported to the NRC during the IPEEE and USI A-46 resolution phase, were required as a result of the recent IPEEE adequacy review.
As stated in DNC's March 31, 2014 letter to the NRC, documentation demonstrating the appropriate capacity of either of these items could not be located; hence, the HCLPF evaluations for each of these components were reconstituted. A summary of these two evaluations is provided below.
Chilled Water Sur-qe Tank The Chilled Water Surge Tank is a vertical cylindrical tank that is 3'-9 1/4" long with an 18" outside diameter. The tank is supported on four 2.5" x 2.5" x 1/4" angles each welded to a 4" x 4" x 1/2" base plate. Each base plate has one anchor bolt to the floor. The anchorage of this tank was reported in the IPEEE submittal with a HCLPF capacity of 0.22g and was identified as an item for follow-up evaluation. This HCLPF calculation was based on conservatively assuming that the four 5/8" diameter anchor bolts were WEJ-IT wedge-type anchors. During the resolution of USI A-46, as documented in the screening evaluation work-sheet (SEWS) for this tank, the anchors were subsequently identified to be Hilti Kwik Bolts. The IPEEE open item associated with the Chilled Water Surge Tank was reported as closed in DNC letter Serial Number 04-398 dated August 13, 2004, however, documentation revising the HCLPF capacity could not be located. Hence, the calculation of HCLPF capacity was reconstituted, confirming HCLPF >0.25g.
In the initial HCLPF calculation that concluded the HCLPF capacity to be 0.22g, the allowable capacities for shear and tension had been reduced by a knock-down factor (KDF) applicable to the WEJ-IT anchor of 0.75 per the guidance of EPRI Report NP-5228-SL, Table 2.15. To confirm the bolt type documented in the USI A-46 SEWS, a walkdown
Serial No 14-350 Docket No. 50-336 Attachment 1, Page 4 of 6 of the tank anchorage was recently completed by a Seismic Qualification Utility Group (SQUG)-trained Seismic Capacity Engineer which concluded the bolts were Hilti Kwik Bolt expansion anchors and not WEJ-IT wedge-type anchors. In accordance with the SQUG Generic Implementation Procedure (GIP) Table C.2-2 and also EPRI NP-5228-SL, a KDF of 1.0 is justified for the tensile and shear capacities of Hilti Kwik Bolt expansion anchors.
Accordingly, the HCLPF capacity was calculated to be greater than the plant HCLPF capacity of 0.25g.
Battery Racks DB1 and DB2 The MPS2 125V DC Main Station Batteries DB1 and DB2 are supported by four battery racks, two located in the East Battery Room (DB1) and two located in the West Battery Room (DB2) in the Auxiliary Building. The battery racks consist of a two step frame. Each step carries a row of battery cells. These racks were reported to have a HCLPF capacity of 0.13g in the MPS2 IPEEE submittal based on the anchorage capacity of the battery racks and were identified as items for follow-up evaluation. This low capacity was governed by the battery racks located on the north side of both battery rooms. It resulted because of the reductions due to large gaps identified between the anchors and the concrete. As identified in the IPEEE submittal report, modifications were required to increase the capacity of the racks. Subsequent modifications were made to the north DB1 and DB2 racks to add seismic restraints. However, no modifications were necessary for the south DB1 and DB2 racks, for which the gaps were smaller. A design basis calculation was prepared to evaluate the adequacy of the racks for design basis loading and it was concluded that the modified north racks and the existing south racks were adequate. The IPEEE open item associated with the battery racks was reported as closed in Northeast Nuclear Energy Company letter Serial Number B17588 dated December 31, 1998, however no documentation could be located to indicate that the modifications for the north racks increased the HCLPF capacity > 0.25g; similarly, no documentation could be located to indicate that the south racks as-is have HCLPF capacity > 0.25g. Hence, the HCLPF capacity calculation was reconstituted.
For the unmodified south DB1 and DB2 battery racks, the largest gap between the anchors and the concrete floor was reported to be /" at two of the anchors on the south DB1 rack. The south DB2 rack had gaps up to 3/8" at some of the anchors. Recent walkdowns were performed to verify that the magnitudes of the gaps on the south side battery racks are unchanged from those previously measured during USI A-46/IPEEE Programs. The south racks were evaluated for the seismic demand corresponding to the IPEEE Review Level Earthquake (RLE). The HCLPF capacities for the anchorage, accounting for the reduction in capacity for the measured gaps, were calculated to be greater than the plant HCLPF capacity of 0.25g.
The north battery racks had been modified due to large gaps identified between the rack anchorage and concrete during the resolution to USI A-46 and IPEEE. Modifications were completed at that time to add a seismic brace in the longitudinal direction of the each rack to resist longitudinal seismic loads of the upper step battery cells. Further, two-bolt base plates were added at each front-to-back rack frame to provide a support to resist front-to-back seismic loads, as well as the longitudinal seismic shear loads of the lower step
Serial No 14-350 Docket No. 50-336 Attachment 1, Page 5 of 6 battery cells. These modifications to the north battery racks were confirmed to be installed as-designed by recent engineering walkdown. These modifications were not reflected in the 0.13g HCLPF capacity reported in the IPEEE submittal. The modifications offset the measured gaps by significantly reducing the shear loads applied to the anchor bolts which thereby reduces the potential for bolt bending. The reconstituted evaluation concluded that, by virtue of these modifications and the resulting significant reduction in anchor bolt shear loads, the north racks HCLPF capacity is also greater than the plant HCLPF capacity of 0.25g.
Request 2 Table 7.1-1, Opportunitiesfor Safety Enhancements,of the IPEEEsubmittal for MPS2 lists two SSCs identified as "items to be resolved". It is written in Table 7.1-1 that these two items are on the USI A-46 Safe Shutdown Equipment List (SSEL) and were being tracked under USI A-46. It is also written in Table 7.1-1 that the IPEEE program would support resolution of these items by providing relative risk significance of this issue in relation to all other USI A-46 issues. One of these two items was resolved with the Near Term Task Force 2.3 walkdowns. The remaining item is:
- Air operated valve 2-CHW-11, which has a heavy yoke that is independently braced.
The NRC staff requests the following:
- Detailed description on how was this item was resolved and what is its safety significance, if any, in terms of the plant IPEEEHCLPF of 0.25g.
DNC Response Air operated valve 2-CHW-1 1 is a part of the MPS2 Vital Chilled Water (CHW) System.
This system functions to provide chilled water to the Vital DC Switchgear Ventilation System for DC Switchgear Room cooling under emergency conditions. The vital CHW system is safety-related and seismic Category I. The vital CHW system has two trains of chilled water, each supplying the respective train of the Vital DC Switchgear Ventilation System. The Vital DC Switchgear Ventilation System, along with the associated vital CHW system, was determined to be a support system for the purposes of the IPEEE program evaluations. The Vital DC Switchgear Ventilation System and CHW system are not frontline systems, and do not directly affect the safe shutdown paths evaluated in the IPEEE Summary Report.
Valve 2-CHW-1 1 is designed to automatically close in an emergency condition in order to provide an isolation boundary between the vital CHW and the non-safety related, non-vital CHW subsystem. Failure of this valve to close, along with a pressure boundary failure of the non-safety related portion of the chilled water system, could result in failure of one of
Serial No 14-350 Docket No. 50-336 Attachment 1, Page 6 of 6 two trains of vital CHW to perform its safety function. However, the redundant vital CHW train would remain capable of providing chilled water to the respective Vital DC Switchgear Ventilation System such that the room cooling function would be maintained. In addition, a manual isolation valve (2-CHW-145) adjacent to 2-CHW-1 1 could be operated locally to provide the system isolation boundary.
Valve 2-CHW-1 1 was identified during reviews supporting the IPEEE Program as an opportunity for a safety enhancement item to be resolved. The valve actuator was determined to be supported independently from the piping system (i.e., braced directly to the structure) during the reviews and listed for further evaluation in the IPEEE Summary Report, Table 7.1-1.
The valve actuator and the piping near the valve body, although supported independently, are attached to the same structure such that stresses due to seismic differential displacements are minimal. This item was evaluated during the USI A-46 Program and determined to meet design basis requirements. The resolution of this item was completed and closure of the item was reported to the NRC in Northeast Nuclear Energy Company letter B17558 dated December 31, 1998.
As discussed above, the failure of this valve only affects a single train of a two train system such that the support function to provide Vital DC Switchgear Room cooling would be maintained despite failure of the valve. Also, the train isolation boundary can be accomplished by closure of an adjacent single manual isolation valve. As such, valve 2-CHW-1 1 has low safety significance related to the safe shutdown paths evaluated in the IPEEE Program. Therefore, the seismic capacity of valve 2-CHW-1 1 does not affect the MPS2 IPEEE plant HCLPF capacity of 0.25g.