ML14043A116
| ML14043A116 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 01/30/2014 |
| From: | Powell G T South Texas |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NOC-AE-13003068, TAC MF1110, TAC MF1111 | |
| Download: ML14043A116 (10) | |
Text
Nuclear Operating CompanySouth Texas Project Electric Generating Station PO Bav 289 Wadswlorth.
T7&as 77483 _/vv_--January 30, 2014NOC-AE-13003068 10 CFR 50.54(f)U.S. Nuclear Regulatory Commission Attention:
Document Control DeskWashington, DC 20555-0001 South Texas ProjectUnits 1 & 2Docket Nos. STN 50-498, STN 50-499STPNOC Update to Response to NRC 10 CFR 50.54(f)
Request for Information Regarding Near-Term Task Force Recommendation 2.3, Flooding
-Review of Available Physical Margin(APM) Assessments (TAC Nos. MF1110 and MF1111)
References:
- 1. Letter from NRC to All Power Reactor Licensees, "Request for Information Pursuant to Title 10 of the Code of Federal Regulations 50.54(f)
Regarding Recommendations 2.1, 2.3 and 9.3, of the Near-Term Task Force Review ofthe Insights from the Fukushima Dai-ichi Accident",
March 12, 2012(ML12056A046)
- 2. Letter from NRC to A.P. Heymer, NEI, "Endorsement of Nuclear EnergyInstitute (NEI) 12-07, 'Guidelines for Performing Verification Walkdowns ofPlant Flood Protection Features"',
May 31, 2012 (ML12144A142)
- 3. Letter from D.W. Rencurrel, STPNOC, to NRC Document Control Desk,"Final Response to NRC Request for Information Pursuant to 10 CFR50.54(f)
Regarding the Flooding Aspects of Recommendation 2.3 of theNear-Term Task Force Review of Insights from the Fukushima Dai-IchiAccident",
November 26, 2012 (ML1 2340A1 56)4. Letter from NRC to All Power Reactor Licensees, "Request for Additional Information Associated with Near-Term Task Force Recommendation 2.3,Flooding Walkdowns",
December 23, 2013 (ML1 3325A891)
On March 12, 2012, the NRC staff issued Reference 1 requesting information pursuant to Title10 of the Code of Federal Regulations 50.54(f).
Enclosure 4 of that letter contains specificRequested Information associated with Near-Term Task Force Recommendation 2.3 forFlooding.
Per Reference 2, the NRC endorsed Nuclear Energy Institute (NEI) 12-07,"Guidelines for Performing Verification Walkdowns of Plant Flood Protection Features,"
datedMay 31, 2012. By Reference 3, South Texas Project Nuclear Operating Company (STPNOC)submitted the final report in response to the request for information.
AV~STI: 33801033 NOC-AE-13003068 Page 2 of 3NEI 12-07 requires that licensees define "small margin",
assess the available physical margin(APM) associated with flood protection
- features, determine if the margin provided is small, andevaluate whether any of the margins have potentially significant consequences.
Those withpotential consequences are to be documented and resolved through the corrective actionprocess.
The results of this effort are to be maintained on site for future NRC audits.Following the NRC staff's initial review of the walkdown
- reports, regulatory site audits wereconducted at a sampling of plants. Based on the walkdown report reviews and site audits, thestaff identified additional information necessary to allow them to complete its assessments.
Accordingly, by Reference 4 the NRC staff has issued a request for additional information (RAI)which licensees are required to respond by January 31, 2014.The RAI questions and the STPNOC responses are provided in the enclosed attachment.
There are no commitments in this letter.If there are any questions regarding this letter, please contact Wendy Brost at (361) 972-8516 orme at (361) 972-7566.
I declare under penalty of perjury that the foregoing is true and correct.Executed on30. 7at-4G.T. PowellSite Vice President web
Attachment:
- 1. STPNOC Update to Response to NRC 10 CFR 50.54(f)
Request forInformation Regarding Near-Term Task Force Recommendation 2.3, Flooding
-Review of Available Physical Margin (APM) Assessments NOC-AE-1 3003068Page 3 of 3cc:(paper copy)(electronic copy)Regional Administrator, Region IVU. S. Nuclear Regulatory Commission 1600 East Lamar Boulevard Arlington, TX 76011-4511 Balwant K. SingalSenior Project ManagerU.S. Nuclear Regulatory Commission One White Flint North (MS 8 B13)11555 Rockville PikeRockville, MD 20852NRC Resident Inspector U. S. Nuclear Regulatory Commission P. 0. Box 289, Mail Code: MN1 16Wadsworth, TX 77483Jim CollinsCity of AustinElectric Utility Department 721 Barton Springs RoadAustin, TX 78704A. H. Gutterman, EsquireMorgan, Lewis & Bockius LLPBalwant K. SingalU. S. Nuclear Regulatory Commission John RaganChris O'HaraJim von SuskilNRG South Texas LPKevin PolioRichard PehaL.D. BlaylockCity Public ServicePeter NemethCrain Caton & James, P.C.C. MeleCity of AustinRichard A. RatliffRobert FreeTexas Department of State Health Services Attachment 1NOC-AE-1 3003068Page 1 of 7STPNOC Update to Response to NRC 10 CFR 50.54(f)
Request for Information Regarding Near-Term Task Force Recommendation 2.3, Flooding
-Review of Available Physical Margin(APM) Assessments Note: References described in this Attachment are found at the end of the Attachment.
APM RAI Question 1:Confirmation that the process for evaluating APM was reviewedSTPNOC Response:
STPNOC has reviewed the process used to evaluate the APM of flood protection features (FPF) atthe South Texas Project Electric Generating Station (STP 1 & 2).APM RAI Question 2:Confirmation that the APM process is now or was always consistent with the guidance in NEI 12-07and discussed in this RAI.STPNOC Response:
The original walkdown effort, documented in Reference 1, was performed in accordance with theguidance provided in NEI 12-07. This RAI response provides additional clarifications which confirmconsistency of the physical margin analysis with NEI 12-07 and the NRC guidance discussed in theRAI.APM RAI Question 3:If changes are necessary, a general description of any process changes to establish thisconsistency.
STPNOC Response:
No changes are necessary to establish consistency with NEI 12-07.APM RAI Question 4:As a result of the audits and subsequent interactions with industry during public meetings, NRC staffrecognized that evaluation of APM for seals (e.g., flood doors, penetrations, flood gates, etc.) waschallenging for some licensees.
Generally, licensees were expected to use either Approach A orApproach B (described below) to determine the APM for seals:
Attachment 1NOC-AE-1 3003068Page 2 of 7a) If seal pressure ratings were known, the seal ratings were used to determine APM (similarto example 2 in Section 3.13 of NEI 12-07). A numerical value for APM was documented.
No further action was performed if the APM value was greater than the pre-established small-margin threshold value. If the APM value was small, an assessment of "significant consequences" was performed and the guidance in NEI 12-07 Section 5.8 was followed.
b) If the seal pressure rating was not known, the APM for seals in a flood barrier is assumedto be greater than the pre-established small-margin threshold value if the following conditions were met: (1) the APM for the barrier in which the seal is located is greater thanthe small-margin threshold value and there is evidence that the seals weredesigned/procured, installed, and controlled as flooding seals in accordance with theflooding licensing basis. Note that in order to determine that the-seal has been controlled as a flooding seal, it was only necessary to determine that the seal configuration has beengoverned by the plant's design control process since installation.
In this case, the APM forthe seal could have been documented as "not small".As part of the RAI response, state if either Approach A or Approach B was used as part of the initialwalkdowns or as part of actions taken in response to this RAI. No additional actions are necessary ifeither Approach A or B was used.If neither Approach A or B was used to determine the APM values for seals (either as part of thewalkdowns or as part of actions taken in response to this RAI), then perform the following twoactions:" Enter the condition into the CAP (note: it is acceptable to utilize a single CAP entry to capturethis issue for multiple seals). CAP disposition of "undetermined" APM values for seals shouldconsider the guidance provided in NEI 12-07, Section 5.8. The CAP disposition shouldconfirm all seals can perform their intended safety function against floods up to the currentlicensing basis flood height. Disposition may occur as part of the Integrated Assessment.
Ifan Integrated Assessment is not performed, determine whether there are significant consequences associated with exceeding the capacity of the seals and take interim action(s),
if necessary, via the CAP processes.
These actions do not need to be complete prior to theRAI response.
" Report the APM as "undetermined" and provide the CAP reference in the RAI response.
STPNOC Response:
The STPNOC analysis of the flooding protection feature (FPF) program compliance with NEI 12-07is based on several elements.
" The site configuration management and design change programs assure the FPFs for STP I& 2 are designed,
- procured, installed, maintained and controlled to the required protection forthe design-basis flood level.* The review of the APM performed for this RAI confirmed that these FPFs provide the APMnecessary to assure the plant design-basis flood level, established in the UFSAR, will not beexceeded.
" Due to the availability of recent additional flooding analyses for the site, the analysis alsoevaluated the conservatism of the current licensing basis flood levels and established thereis additional margin due to this conservatism, further demonstrating that the design-basis flood level will not be exceeded.
Attachment 1NOC-AE-1 3003068Page 3 of 7NEI 12-07, Section 5.8, "Documentation of Available Physical Margin" indicated that the size of themargin should be evaluated and based on issues such as complexity and uncertainty of thelicensing basis flood evaluation (Reference 2). STP I & 2 has access to three recent flood analysesfor the site, based on more recent flooding analysis methodologies and modeling technologies, which reduce the uncertainty associated with the design-basis flood level and demonstrate that thedesign-basis flood level is higher than would be required by the use of current analysis techniques.
These more recent analyses establish that the flooding levels are not expected to reach the currentlicensing basis flood level.The impact of this conclusion in the APM analysis for STPI & 2 is that, while APM is a comparison against the design-basis flood level, there is additional margin associated with the conservatism ofthe design-basis flood level which should be added to the APM and considered in the evaluation ofwhether the design-basis flood level is sufficient to provide protection against postulated floodingevents.On this basis, the STPNOC program meets the requirements of Approach A, as defined in this RAI.The pressure ratings of all of the FPFs are known and documented in the flooding protection designdocuments and the corresponding technical information is available in plant records.
The reviewperformed in this RAI has established a single bounding APM value applicable to all of the siteFPFs.The bounding APM confirms that the design-basis flood level is not exceeded.
While the margin formost items is significantly larger than the "small margin" established in Reference 3, there are alimited number of items where the design-basis for the FPFs is equal to, but does not exceed, thedesign-basis flood level. The analysis, based on using current methodologies and recently available flooding
- analyses, has established there are no "significant consequences" for these installations, since the excessive conservatism of the design-basis flood level provides sufficient additional marginso the design-basis flood level is not expected to be exceeded.
STP Configuration Management and Design Change ProgramsAt STP 1 & 2, FPF design characteristics and pressure ratings are known and contained incontrolled design documents that define the key characteristics of each FPF, including technical information about the flooding pressure rating. The FPFs in these programs have been, andcontinue to be, designed,
- procured, installed, and controlled in accordance with the floodinglicensing basis.The site procedures detailing these programs are as follows:* Site procedure OPGPO3-ZA-0109, "Configuration Management Program" defines thecomponents of the S TPNOC configuration management program (CMP).o The CMP consists of a set of controlled processes to ensure that designated facilityStructures,
- Systems, Components and Supporting Software (SSCS) conform to licenseand design requirements and that their physical and functional characteristics arecorrectly reflected in design, operating, maintenance, procurement and trainingdocuments.
o The CMP applies a graded approach to scope and control of SSCS via Design Control,Configuration
- Control, and Exemptions.
- Design Control -A formal process for controlling design attributes, requirements and basis changes to the physical plant and design documentation which ensuresadherence to the requirements of IOCFR50.
Attachment 1NOC-AE-1 3003068Page 4 of 7" Configuration Control -The process of maintaining conformance betweendocumentation and associated SSCS." Exemptions
-SSCS or portions
- thereof, which have been specifically approved bythe Vice President, Engineering to be excluded from CMP entirely or to variousdegrees.
These SSCS or portions thereof may therefore be subject to DesignControl and/or Configuration Control and/or Exempt from all CMP controls.
- Site procedure OPGPO4-ZA-0328, "Engineering Document Processing",
establishes generaladministrative requirements for classifying, preparing,
- revising, retiring,
- voiding, andsuperseding engineering related documents.
o Part of this procedure requires assignment of a Priority to station documents
-documents associated with the "flood protection features" fall within priority 2-5.Therefore, documentation for these features is defined as "design controlled" and theflood protection features are in design control.* Site procedure OPGPO4-ZE-0309, "Design Change Package",
provides the controls andprocesses to implement permanent design changes (both physical and non-physical) to theplant. This procedure applies to the processing of permanent Design Changes to Structures,
- Systems, and Components (SSCs) within Design Control per the CMP.o All changes to the flood protection features are performed and implemented under thedesign and configuration management program.* Site procedure OPGPO4-ZE-0312, "Design Change Implementation",
establishes requirements for controlling the implementation,
- testing, and processing of documentation associated with physical changes to Systems, Structures and Components (SSCs) in theplant. This procedure is applicable to all Major and Minor Modifications, and Minor ChangeDesign Change Package (DCP), as determined by the cognizant Implementation and/orDesign Organizations.
o Any change to a flood protection feature due to redesign or maintenance activities isevaluated for impact to the design/licensing basis.* Site procedure OPGPO3-ZA-0090, "Work Control Program",
describes the high levelrequirements and process for managing work at the station through work identification, workscreening and processing, work activity scheduling, work activity
- planning, and work activityexecution and closeout.
The Work Process Program applies to activities performed on plantSSCs included in the CMP.The controlled FPF design documents identify the key characteristics of each item, including information such as location, type, supplier, model number. The corresponding technical information for each type of FPF, such as pressure rating, pressure test results, and supplier technical information is available in the design documents.
Since all FPFs are controlled by an approved site configuration management and design changeprogram, it can be concluded that they meet the flooding design-basis requirements.
Therefore, S TPNOC is able to conclude that the bounding value for APM for the S TP 1 & 2 site is greater thanor equal to zero feet and meets the design-basis.
Analysis of the Available Physical MarginSTPNOC has determined there are no significant safety consequences associated with the smallbounding site APM due to the conservative design-basis flood for STP I & 2. This additional conservative margin can be shown by more recent flood analyses for the site.
Attachment 1NOC-AE-1 3003068Page 5 of 7As described in the Updated Final Safety Analysis Report (UFSAR) for STP 1 & 2, the design-basis flood for the plant was established by considering an extremely improbable failure of the MainCooling Reservoir (MCR). This MCR breach modeling analysis incorporated a number ofconservative assumptions that produced conservative and bounding design-basis flood levels at thesafety related facilities.
Some of the notable assumptions include:" A several hundred feet long section of the failed MCR embankment would translate downstream several tens of feet off from its original location.
This failure scenario was initially modeled by assuming the removal of a 400ft long embankment section.
To provide furtherconservatism, the postulated breach section was increased from 400ft to 4000ft,incrementally, to determine the most critical flooding impact to the site. An approximately 2000ft breach was found to produce the highest flood levels, which were subsequently adopted as the design-basis flood levels.* Although historical embankment and dam failure events typically involve a time lapse fromthe onset of failure to full development of breach, an instantaneous removal of the section ofthe embankment was conservatively adopted for the STP analysis instead of a more realistic breach rate.* The MCR breach analysis did not take any credit for flow retardation and dispersion that, inreality, would be provided by the circulating water intake pipes, circulating water intake anddischarge structures, and various other obstructions between the embankment and plantstructures.
" The upstream model boundaries were specified to correspond to a constant initial water levelof the MCR (50.5ft MSL). The use of a static water level boundary condition is highlyconservative, in that the water level at the breach is expected to drop with time with thereservoir storage is being depleted during an actual embankment failure event.As described in the Flood Hazard Reevaluation Report (Reference 3), significant new flooding levelinformation is available to demonstrate the conservatism of the current design-basis flood levelsdiscussed above. This conservatism is corroborated by a qualitative comparison with the resultsfrom three recent MCR breach model studies.
The three recent model studies are:(1) A MCR breach modeling analysis using the FLDWA V breach computer program developed by the National Weather Service (NWS) in conjunction with the RMA2 hydrodynamic computer program developed by the United States Army Corps of Engineers (USA CE),adopted a conservative but more realistic breaching
- scenario, both in the length of thebreach section and the breach rate (i.e., typically expressed as time to full breach),
than theUFSAR analysis.
(2) An independent MCR breach model analysis using the Delft3D-FLOW hydrodynamic computer program.
It adopts the same conservative approach as the UFSAR analysis.
Inparticular, the length of the breach section (also referred to as the breach width) wasincrementally increased in the simulation to maximize the resulting flood levels at the pointsof interests, and full breach was assumed to occur instantaneously.
This analysis is includedhere as another point of reference to demonstrate the conservatism in the current flooddesign-basis for STP I & 2.(3) A 2012 MCR breach flooding analysis conducted for STP 1 & 2 to acquire a betterunderstanding of the site conditions that would be expected following the very unlikely eventof a failure of the MCR embankment (Reference 4). The simulations were performed usingthe BREACH modeling program of NWS and the USA CE RMA2 hydrodynamic computerprogram.
Attachment 1NOC-AE-1 3003068Page 6 of 7These recently completed modeling studies show reductions in the maximum water levels usingcurrent modeling techniques and bases versus the design-basis'flood level established when theplant was initially licensedConclusion In summary, the analysis of the physical margin has achieved the following:
- The flooding protection features control program has been confirmed to assure that thesefeatures are designed,
- procured, installed, maintained and controlled to assure they continueto provide the protection required to assure the current design-basis flood levels is notexceeded.
- The review of the physical margin has confirmed that the current licensing-basis flood levelwill not be exceeded by the flooding level which the plant will experience.
" Recent site flood analyses have been used to establish that the current licensing-basis floodlevels are very conservative.
Due to the conservative design-basis flood for STP I & 2STPNOC has determined that there are nosignificant safety consequences associated with the small bounding site APM.
Attachment 1NOC-AE-1 3003068Page 7 of 7References
- 1. Letter from D. W Rencurrel, STPNOC, to NRC Document Control Desk, "Final Response to NRCRequest for Information Pursuant to 10 CFR 50.54(o Regarding the Flooding Aspects ofRecommendation 2.3 of the Near-Term Task Force Review of Insights from the Fukushima Dai-Ichi Accident',
November 26, 2012 (ML 12340A 156)2. Letter from J.H. Riley, NEI, to NRC Document Control Desk, NEI 12-07, Revision 0, "Guidelines for Performing Verification Walkdowns of Plant Flood Protection Features",
May 2012(ML12144A401)
- 3. Letter from G. T. Powell, STPNOC, to NRC Document Control Desk, "Response to NRC Requestfor Information Pursuant to 10 CFR 50.54(0 Regarding Recommendation
- 2. 1 Flooding of theNear Term Task Force Review of Insights from the Fukushima Dai-ichi
- Accident, Enclosure 2,Required Response 2, Flood Hazard Reevaluation Report",
March 11, 2013 (ML13079A806)