ML14206B064
| ML14206B064 | |
| Person / Time | |
|---|---|
| Site: | Fort Calhoun  |
| Issue date: | 07/25/2014 |
| From: | Cortopassi L Omaha Public Power District |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LlC-14-0087 | |
| Download: ML14206B064 (7) | |
Text
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jjjjjjjj Omaha Public Power Oislrict 444 South 1(fh Street Mall Omaha, NE 68102-2247 LlC-14-0087 July 25, 2014 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001 Fort Calhoun Station, Unit No. 1 Renewed Facility Operating License No. DPR-40 NRC Docket No. 50-285 10 CFR 50.54(f)
Subject:
OPPD Response to NRC Request for Additional Information Regarding the Fort Calhoun Station Unit No. 1 Seismic Hazard and Screening Report
Reference:
Letter from NRC (M. Balazik) to OPPD (L. P. Cortopassi), Fort Calhoun Station Unit 1 - Request for Additional Information Associated With Near-Term Task Force Recommendation 2.1, Seismic Hazard and Screening Report, dated July 16,2014 (NRC-14-0089)
This letter is responding to the NRC staff's request for additional information (RAI) regarding the Seismic Hazards and Screening Report at Fort Calhoun Station. The Omaha Public Power District's (OPPD) response to the NRC RAI is attached.
This letter contains no new regulatory commitments.
If you should have any questions regarding this submittal or require additional information, please contact Mr. Bill R. Hansher, Supervisor-Nuclear Licensing, at 402-533-6894.
I declare under penalty of perjury that the foregoing is true and correct.
Executed on July 25, 2014.
ouis P. Cortopassi Site Vice President and CNO LPC/JKG/brh
Attachment:
OPPD Response to NRC Request for Additional Information Regarding the Fort Calhoun Station Unit No. 1 Seismic Hazard and Screening Report Employment with Equal Opportunity
LlC-14-0087 Attachment Page 1 OPPD Response to NRC Request for Additional Information Regarding the Fort Calhoun Station Unit No.1 Seismic Hazard and Screening Report
LI C-14-0087 Attachment Page 2 REQUEST FOR ADDITIONAL INFORMATION NEAR-TERM TASK FORCE RECOMMENDATION 2.1, SEISMIC HAZARD AND SCREENING REPORT OMAHA PUBLIC POWER DISTRICT FORT CALHOUN STATION, UNIT 1 DOCKET NO. 50-285 On March 12, 2012, the U.S. Nuclear Regulatory Commission (NRC) issued a request for information pursuant to Title 10 of the Code of Federal Regulations, Part 50 (10 CFR),
Section 50.54(f) (hereafter referred to as the 50.54 (f) letter) (Agencywide Documents Access and Management System (ADAMS) Accession No. ML12053A340). The purpose of the request was to gather information concerning, in part, the seismic hazards at operating reactor sites and to enable the NRC staff to determine whether licenses should be modified, suspended, or revoked. To respond to the 50.54(f) letter, Omaha Public Power District (OPPD) committed to follow the Electric Power Research Institute (EPRI)
Report, "Seismic Evaluation Guidance: Screening, Prioritization and Implementation Details (SPID) for the Resolution of Fukushima Near-Term Task Force Recommendation 2.1: Seismic," (ADAMS Accession No. ML12333A170) as supplemented by the EPRI Report, "Seismic Evaluation Guidance: Augmented Approach for the Resolution of Fukushima Near-Term Task Force (NTTF) Recommendation 2.1: Seismic" (referred to as the Expedited Approach) (ADAMS Accession No. ML13102A142). OPPD submitted the re-evaluated seismic hazards (ADAMS Accession No. ML14097A087) for Fort Calhoun Station (FCS) in March 2014. The NRC staff conducted the screening and prioritization review of the submittal by assessing OPPD's screening evaluation and hazard analysis utilizing the endorsed SPID guidance. Accordingly, during the NRC screening and prioritization process, the staff identified that a determination could not be made and interactions with OPPD were needed to reach resolution. The staff identified FCS as a "conditional screen-in" for the purposes of prioritizing and conducting additional evaluations. On May 9,2014, the NRC staff issued a letter (ADAMS Accession No. ML14111A147) documenting the NRC staff's screening results.
In accordance with the SPID and Expedited Approach guidance, the re-evaluated seismic hazard determines if additional seismic risk evaluations are warranted for a plant. The SPID guidance provides criteria for a plant with ground motion response spectra (GMRS) above the safe shutdown earthquake, but bounded by the Individual Plant Examination for External Events (IPEEE) capacity spectrum. To use the IPEEE capacity spectrum to screen out of conducting a seismic risk evaluation, the licensee needed to demonstrate the adequacy of FCS's IPEEE evaluation by meeting the criteria in the SPID. If the IPEEE capacity is greater than the GMRS in the 1-10 Hz range, the plant screens out of conducting a seismic risk.
The following additional information is requested to support the NRC's final screening determination for FCS based on IPEEE adequacy:
LlC-14-0087 Attachment Page 3
- 1.
Prior to restart of the unit, the as found condition of Class I structural members inside containment and in the auxiliary building were determined to be outside the current licensing basis.
These issues are documented in a May 14, 2014, inspection report, "Fort Calhoun -
NRC Integrated Inspection Report Number 05000285/2014007" (ADAMS Accession No ML14134A410). In the FCS seismic hazard and screening report submittal of March 31, 2014, the licensee indicated that it will not perform a risk evaluation because the FCS Individual Plant Examination of External Events (IPEEE) Hazard Spectra (IHS) exceeds the calculated Ground Motion Response Spectra (GMRS).
To support your conclusion, please describe how these structural elements were evaluated and found to have sufficient seismic capacity consistent with the IHS.
OPPD Response:
As part of the post-restart commitments stated in the Integrated Report to Support Restart of the Fort Calhoun Station and Post-Restart Commitments for Sustained Improvement, (Reference 1)
OPPD committed to evaluate the structural design margin for containment internal structures (CIS) and resolve any deficiencies to restore full structural design margin as described in the FCS licensing basis (Enclosure 2 of Reference 1). The commitment noted for the CIS element response for beam 22A and 22B is being addressed through several proposed modifications which will be performed during the 2015 refueling outage. Subsequent modifications are being planned for the 2016 refueling outage and being tracked through the corrective action program (CAP). Auxiliary building structural design basis issues are also being resolved through CAP.
Once the modifications are completed then the condition is expected to restore the design basis including IPEEE.
As noted in the Reference 2, Fort Calhoun Station Closure of Confirmatory Action Letter:
"In May 2012, OPPD identified discrepancies between design calculations and design drawings for a concrete beam and a floor slab. Based on the results from its extent-of-condition review, OPPD identified other containment internal structure deficiencies that did not conform to the licensing basis. Although portions of the containment internal structure were found to be non-conforming to the design basis, OPPD was able to demonstrate the structure was operable and fully capable of performing its function under all design basis accident loading conditions.
The NRC determined that OPPD appropriately evaluated the cause and extent-of-condition for this issue and independently verified that OPPD has actions in place via the corrective action process to restore the containment internal structure to its design criteria in a timely manner.
Following completion of NRC inspection activities, on November 7, 2013, the IMC 0350 Panel and NRC staff involved in reviewing Restart Checklist Item 2.d conducted discussions and determined this item had been adequately addressed by OPPD and therefore closed it. "
For the IPEEE assessment, the containment, CIS and auxiliary building were screened out at the 0.3g peak ground acceleration (PGA) in accordance with EPRI NP-6041-SL Seismic Margin Assessment (SMA) methodology (Reference 7). Table 2-3 of NP-6041 allows the containment,
LI C-14-0087 Attachment Page 4 CIS and concrete or steel frame structures that have been dynamically analyzed for the safe shutdown earthquake (SSE) not less than 0.1 g PGA to be screened out with a High Confidence of Low Probability of Failure (HCLPF) of 0.3g PGA capacity.
The FCS structures were seismically (dynamically) analyzed and designed for an SSE with a 0.17g PGA in accordance with their licensing basis requirements. This screening is valid regardless of the concrete and steel design code year, meaning the FCS structures meet the IPEEE Hazard Spectrum (IHS) anchored to 0.3g PGA.
Structural design modifications are currently in progress and will be installed during the next two refueling outages. The design modifications will be designed to meet either current licensing basis or an amended licensing basis with respect to use of working stress design for the load cases not including SSE loads. Any amendment of the use of working stress design for the design earthquake (which is the Operating Basis Earthquake) does not affect SSE load cases for which ultimate strength design is utilized at FCS. The I PEEE screening is based solely on the SSE design of plant structures, and with the planned design modifications FCS is expected to meet the SSE design requirements. Therefore, the conclusion is that FCS buildings will satisfy the screening criteria for a 0.3g PGA HCLPF plant once it is in full compliance with its licensing basis.
- 2.
The FCS seismic hazard and screening report submittal indicated that a risk evaluation will not be performed because FCS's IPEEE high confidence of a low probability of failure spectrum exceeds the calculated GMRS.
However, in considering the soil erosion observed during the 2011 flood at the site, please explain if the erosion and related impact could have potentially weakened the foundation supporting materials, and therefore affected the estimation of the site-specific GMRS.
OPPD Response:
Included in the Fort Calhoun Station Integrated Performance Improvement Plan Rev. 3 (Reference 3), OPPD provided the Flooding Recovery Action Plan that documented the actions necessary for the repair and restoration of FCS operations post 2011 flooding.
OPPD documented facility geotechnical and structural assessments in a report herein called "Assessment Report" that was prepared in response to FCS Flooding Recovery Action Plan 4.1 Element, Plant and Facility Geotechnical and Structural Assessment. Soil bore testing, and static and dynamic cone penetration testing were completed to locate and characterize the extent of loose soils. The Assessment Report compared geotechnical data for pre-and post-flood soil and concluded that there was no observable difference in the overall geotechnical conditions at the FCS site. The Assessment Report concluded that the foundation materials had not been disturbed and were not significantly weakened by prolonged inundation during the 2011 flood. Comparison of seismic refraction data from the pre and post flood investigations revealed similar magnitude of seismic wave velocities over the full depth of the overburden soils, and no observable differences in pre and post flood conditions. The Assessment Report identified and evaluated the geotechnical and structural effects of the 2011 flood on Priority 1 and 2 structures at the FCS site. The Priority 1 structures are those structures and systems that directly support plant operations. The Priority 2 structures are those that do not directly support plant operations. The Assessment Report evaluated direct impacts of floodwater from the 2011 Missouri River flood on the soil and/or rock that supports the FCS structures and how that may have negatively impacted those structures.
LlC-14-00B?
Attachment Page 5 The detailed geotechnical and structural assessment was provided to the NRC as part of the Flood Recovery Plan and the action items related to such were identified as closed in Reference
- 4. The action items associated with flooding impact of sub-surface water on soils and structures were closed out by the NRC in two inspection reports (Le., References 5 and 6). The action items included verification of no geotechnical or structural impact to the turbine building, the auxiliary building, or containment due to the 2011 flood. The Assessment Report noted above concluded that further safety related assessments would be performed in a few areas as discussed below.
As part of the 2011 flood and floodwater assessment, further separate evaluations were performed and documented outside the Assessment Report to investigate additional isolated concerns related to potential loss of lateral support and further seismic impacts of the soils.
Calculations and analyses were performed to evaluate lateral and vertical extents of postulated potential Negatively Affected Soil (NAS) under key structures such as the turbine building, the auxiliary building, and containment.
These calculations concluded that even if there were postulated NAS beneath the auxiliary building or containment, the structural integrity would be maintained and the design basis seismic floor response spectra used for equipment qualification remains unaffected. The postulated (exposed) piles were shown to be capable of sustaining the seismic demand and maintaining the structural integrity. Even under the extreme postulation that all piles beneath the auxiliary building were surrounded by potential NAS and up to 10 feet of the piles were completely (laterally) unsupported by the soil, the seismic response of the buildings was found to be less than the original design basis. The evaluation concluded that under worst-case postulated scenarios that the auxiliary building and containment continue to meet the design basis criterion for Class 1 structures. A calculation was also performed that explored the potential postulated effects of NAS on the Alternate Seismic Criteria and Methodologies (ASCM) predicted seismic response results for the turbine building, the auxiliary building, and containment. This study concluded that the potential postulated effect of NAS around the piles to the postulated depth and with the postulated properties below the turbine building, the auxiliary building, and containment is to reduce the seismic response of the structures and the ASCM is considered to remain conservatively bounding. The calculations concluded that from a plant design basis perspective, the soil characteristics were not significantly impacted. However, to ensure consideration for potential postulated NAS under key structures where soil measurements were not taken, the safety related evaluations noted above were performed, which illustrated that the design basis seismic response and integrity were maintained.
The NRC documented review of these safety related calculations in Reference 5.
Since extensive post-flood soil testing and evaluations demonstrated that the plant original design basis is bounded and maintained regarding soil impacts, no reconciliation is required to confirm that the IPEEE curve remains valid for screening. Additionally, the data from the 2012 geotechnical testing was part of the information provided for utilization in the development of the new site Ground Motion Response Spectra (GMRS) curves, which addresses the concern raised by NRC staff regarding soil characteristics considerations for development of the new seismic GMRS curves developed by EPRI (Ref. OPPD Letter to EPRI FCS-FRP-GEN-12-001 dated October 30, 2012 posted on NRC eportal, Transmittal of Soils data, IEEElSSE Seismic Spectra and Control Point Elevation Information). This reference document identifies that the soil and rock dynamic properties used in the new GMRS were taken from site measurements, 196? (original), 2011, and 2012.
LI C-14-0087 Attachment Page 6
References:
- 1.
Letter from OPPD (L. P. Cortopassi) to NRC (Document Control Desk), Integrated Report to Support Restart of Fort Calhoun Station and Post-Restart Commitments for Sustained Improvement. dated December 2,2013 (LlC-13-0164)
- 2.
Letter from the NRC (M. L. Dapas) to OPPD (L. P. Cortopassi), Fort Calhoun Station Closure of Confirmatory Action Letter, dated December 17, 2013 (EA-13-020)(NRC 0155)
- 3.
Letter from OPPD (L. P. Cortopassi) to NRC (Document Control Desk), Fort Calhoun Station Integrated Performance Improvement Plan Rev. 3, dated July 9,2012 (LlC 0098)
- 4.
Letter from NRC (M. L. Dapas) to OPPD (L. P. Cortopassi), Current Status of U.S.
Nuclear Regulatory Commission Inspection Manual Chapter 0350 Panel Fort Calhoun Station Restart Checklist and Basis Documents, dated November 15, 2013 (NRC 0147)(EA-13-020)
- 5.
Letter from NRC (M. Hay) to OPPD (L. P. Cortopassi), Fort Calhoun - NRC Integrated Inspection Report Number (0500028512013016),
dated December 11, 2013 (ML133458304)
- 6.
Letter from NRC (M. Hay) to OPPD (L. P. Cortopassi), Fort Calhoun - NRC Integrated Inspection Report Number (0500028512013005), dated August 9, 2013 (NRC 01 04)(ML133458304)
- 7.
EPRI NP-6041-SL Rev. 1, A Methodology for Assessment of Nuclear Plant Seismic Margin, August 1991