NL-13-0954, Proposed Path to Closure of Generic Safety Issue-191, Assessment of Debris Accumulation on Pressurized-Water Reactor Sump Performance.
| ML13137A131 | |
| Person / Time | |
|---|---|
| Site: | Farley  |
| Issue date: | 05/16/2013 |
| From: | Pierce C Southern Nuclear Operating Co, Southern Co |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| NL-13-0954, GL-04-002 | |
| Download: ML13137A131 (13) | |
Text
Charles R. Pierce Southern Nuclear Regulatory Affairs Director Operating Companv, Inc.
40 Inverness Center Parkway Post Offi ce Box 1295 Birmingham, Alabama 35201 Tel 205. 992 .7872 Fax 205.992.7601 SOUTHERN COMPANY A
May 16, 2013 Docket Nos.: 50-348 NL-13-0954 50-364 U. S. Nuclear Regulatory Commission ATIN: Document Control Desk Washington, D. C. 20555-0001 Joseph M. Farley Nuclear Plant Proposed Path to Closure of Generic Safety Issue-191 ,
"Assessment of Debris Accumulation on Pressurized-Water Reactor Sump Performance"
References:
(1) Generic Letter (GL) 2004-02: Potential Impact of Debris Blockage on Emergency Recirculation During Design Basis Accidents at Pressurized Water Reactors.
(2) December 23, 2010, Staff Requirements - SECY-10-0113 - Closure Options for Generic Safety Issue - 191 , Assessment of Debris Accumulation on Pressurized-Water Reactor Sump Performance.
(3) October 12, 2011, Pressurized Water Reactor Owners Group (PWROG),
Topical Report (TR) WCAP-16793-NP, Revision 2, "Evaluation of Long Term Core Cooling Considering Particulate Fibrous and Chemical Debris in the Recirculating Fluid".
(4) May 4,2012, Nuclear Energy Institute (NEI) to the U.S. Nuclear Regulatory Commission (NRC), Office of Nuclear Reactor Regulation, Director, Division of Safety Systems -
Subject:
GSI-191 - Current Status and Recommended Actions for Closure.
(5) July 9,2012, SECY-12-0093 - Closure Options for Generic Safety Issue 191, Assessment of Debris Accumulation on Pressurized-Water Reactor Sump Performance.
(6) November 15, 2012, Nuclear Energy Institute (NEI) to the U.S. Nuclear Regulatory Commission (NRC), Office of Nuclear Reactor Regulation, Director, Division of Safety Systems -
Subject:
GSI-191 - Revised Schedule for Licensee Submittal of Resolution Path.
(7) November 21,2012, Nuclear Regulatory Commission Review of Generic Safety Issue-191 Nuclear Energy Institute revised Schedule for Licensee Submittal of Resolution Path.
(8) December 14,2012, Staff Requirements - SECY-12-0093 - Closure Options for Generic Safety Issue - 191, Assessment of Debris Accumulation on Pressurized-Water Reactor Sump Performance.
(9) April 8, 2013, Final Safety Evaluation for Pressurized Water reactor Owners Group Topical Report WCAP-16793-NP, Revision 2, "Evaluation of Long-Term Cooling Considering Particulate Fibrous and Chemical Debris in the Recirculating Fluid."
U.S. Nuclear Regulatory Commission NL-13-0954 Page 2 Ladies and Gentlemen:
In Reference (4), NEI highlighted the current industry status and recommended actions for closure of Generic Safety Issue (GSI)-191 based on licensees providing a docketed submittal to the NRC by December 31, 2012, outlining a GSI-191 resolution path and schedule pursuant to the Commission direction in Reference (2). By Reference (6), NEI recommended to NRC that licensees delay submittal of GSI-191 resolution path and schedule until January 31, 2013, or 30 days following placement of both the Commission response to Reference (5) and the NRC staff safety evaluation (SE) on Reference (3) into the public record . In Reference (8) the Commission approved the staff's recommendation in Reference (5) to allow licensees the flexibility to choose any of the three options discussed in the paper to resolve GSI-191 . Further the Commission encouraged the staff to remain open to staggering licensee submittals and the associated NRC reviews to accommodate the availability of staff and licensee resources. The SE Reference (9) for Reference (3) was made publicly available by NRC on April 16, 2013.
An industry template was developed by NEI for the identification of a resolution path and schedule, and to describe defense-in-depth and mitigation measures to support the proposed resolution schedule. The NEI template was used for the development of Enclosure 1 for Joseph M. Farley Nuclear Plant (FNP) Units 1 and 2, and provides a resolution path forward and schedule for resolution, summary of actions completed for GL 2004-02, and defense-in-depth and mitigation measures which will be established and maintained throughout the resolution period.
The NRC commitments contained in this letter are provided as a table in Enclosure 2. If you have any questions, please contact Ken McElroy at (205) 992-7369.
Mr. C. R. Pierce states he is Regulatory Affairs Director of Southern Nuclear Operating Company, is authorized to execute this oath on behalf of Southern Nuclear Operating Company and, to the best of his knowledge and belief, the facts set forth in this letter are true.
Respectfully submitted, C. R. Pierce Regulatory Affairs Director CRP/rmj/lac df!a:: s;y'rit r;t:ethis ~ day of rD ~ , 2013.
NotarY Public My commission expires: If-z-/3
U. Nuclear Regulatory Commission NL-13-0954 Page 3
Enclosures:
- 1. Path Forward and Schedule for Resolution of 91 List Regulatory Commitments cc:
Kuczynski, Chairman, President & CEO Mr. D. Bost, Vice President & Chief Nuclear Officer Mr. T. A. Lynch, President -
Mr. B. L. Ivey, Vice - Regulatory Mr. J. Adams, Vice President - Fleet Operations CFA04.054 Mr. V. M. McCree, Regional Administrator Ms. A. Brown, NRR Project Manager - Farley Mr. K. Niebaum, Senior Resident-Mr. J. Sowa, Senior Resident Farley
Joseph M. Farley Nuclear Plant t'rc)pc)se.a Path to Closure of Generic Safety 91, "Assessment of Debris Accumulation on Pressurized-Water Reactor Sump Performance" Enclosure 1 Path Forward and Schedule for Resolution of GSI-191 NL~13~0954 Path Forward and Schedule for Resolution of GSI~191 Introduction Southern Nuclear Operating Company (SNC) has selected Option Deterministic, for Farley Nuclear Plant (FNP), and intends to refinements to evaluation methods and acceptance criteria. support use of this path, and continued operation for the period required to complete the necessary analysis and testing, SNC has evaluated design and procedural capabilities that exist to identify and mitigate sump strainer and blockage. A description of these detection and mitigative measures are provided later in this document.
Additionally, a summary of existing margins and conservatisms that exist for FNP are also included in this document.
Farley has essentially 100% reflective metal insulation in containment and has only a small amount of fiber in containment, consisting of the fiber content of latent debris, and a limited amount Temp-Mat insulation. With the conservative assumptions on transport and bypass, FNP could exceed 15 grams of fiber per fuel assembly limit specified in WCAP-16793-NP, Revision 2.
Characterization of Strainer Head loss Status SNC previously provided of strainer head loss testing, including impact of chemical effects, in References 1 and The results of this testing demonstrate acceptable results with regard allowable head loss.
Characterization of In-Vessel Effects SNC intends to follow the resolution strategy proposed by Pressurized Water Owners Group (PWROG) for establishing in-vessel debris limits for the type of plant design that exists at FNP, Units 1 and 2.
SNC does not currently have open commitments within the Units 1 and 2 commitment management system to provide additional updates or information to the NRC regarding GL 2004-02.
Resolution Schedule SNC plans to achieve closure of GSI-191 and address 2004-02 per the following schedule.
SNC is currently in the of scheduling a meeting with the NRC to discuss this proposed resolution path.
The Proposed Modification and Testing Schedule, as currently expected, is given below:
- Fall 2013: U1 outage - confirm Temp-Mat location in U1 Zone of Influence (ZOI)
- 201 Evaluate Modifications, develop plan for potential need to replace Temp-Mat
- 1014 301 write spec, get bids, place order, get design drawings
- 3014 - 2015: Design Window
- 3014: Strainer if Required
- 2015: Review
- 2015 - 1016: Work Order Planning
- Within six months of the NRC for the PWROG WCAP that will establish a final determination of scope (if any) of insulation replacement or remediation, SNC will submit a final updated supplemental response to support closure of GL 2004-02 for FNP Unit 1 & 2.
- If SNC determines that proposed testing or analysis resolution path will not viable, then an alternate resolution will discussed with the NRC to gain acceptance of the proposed path and to establish an acceptable completion schedule within 6 months of the NRC for the PWROG WCAP.
- SNC will update the current licensing basis (UFSAR) and complete the identified removal or modification of insulation debris sources in containment per plant modification procedures and processes (10 50.71 (e>> within 18 months following NRC of the updated supplemental response for FNP, Units 1 and To support closure of GSI-191 and to address 2004-02, SNC has completed the following actions for FNP, Units 1 and
- The Temp Mat locations in the Unit 2 ZOI have been confirmed.
- FNP installed the strainers practicable for the space available within containment for each unit. congested nature of the lower containment elevation resulted in the need for significant removal and relocation of structural steel and other eqUipment In addition the in strainer were reduced to a nominally 3/32 inch from the 1/8 inch hole in the original Thus the potential for debris passing through the strainer and causing plugging of the down stream emergency core COOling system (ECCS) equipment is minimized.
FNP contracted with General Electric Company (GE) to provide sump strainers that requirements GL 2004-02. provided FNP with seven horizontal stacked disk strainers 4 of Enclosure 2 to and one stacked disk strainer (see Figure 3 of Enclosure 2 to Reference 2). The strainers were installed in both Unit 1 and Unit 2. Unit 1 has the only vertical stacked strainer installed on the Train Containment Spray pump suction.
-2 to NL-13-0954 Path Forward and Schedule Resolution of GSI-1 91 The strainers for Unit 1 and Unit 2 are located outside the bio-wall between the bio wall and containment outside wall (see Figures 1 and 2 of Enclosure 2 to Reference 2).
This location protects the strainers from missile impacts.
For Unit 1, the passive strainer solution is shown in Figure 1 Enclosure 2 to
- 2. Each strainer assembly for both residual heat removal (RHR) strainers and containment spray system (CSS) A-Train consists of two modular horizontal stacked strainer sub-units connected to the post loss of coolant accident (LOCA) pump suction through piping. The 8-Train strainer assembly consists of modular vertical disk strainer sub-units connected to a plenum that assists in directing flow to the post LOCA pump suction inlet located within the plenum boundary.
The RHR strainer assembly, either A-Train or 8-Train, is composed of two strainer sub units per sump, each consisting of stacked disks that are 40" X 40" and provide a total of approximately 878 of perforated plate surface area. The CSS A-Train strainer assembly consists of one strainer sub-unit with (22) 40" X 40" stacked disks and the other with (10) 40" X 40" stacked disks, providing a total of approximately 638 fF of perforated plate surface area. The CSS 8-Train strainer assembly is composed of strainer sub-units, each with (13) 30" X 30" vertical stacked disks, and provides a total of approximately 389 ft2 of perforated plate surface area.
For Unit the solution is shown in Figure strainer assembly for RHR and CSS consists of two modular horizontal stacked disk strainers connected to the sump through piping. RHR strainer assemblies, both A-Train and are composed of two strainers per sump, each consisting of stacked disks that are 40" X 40" and provide a total of approximately 878 ft2 of perforated surface area. The A-Train strainer assembly consists of one strainer with (22) 40" X 40" stacked disks and the other with (10) 40" X 40 disks, providing a total of approximately 638 ft2 of perforated plate surface area. The CSS 8-Train strainer assembly is composed of two strainers, one with (10) 40" X 40" stacked disks and the other with (22) X 30" disks, and provides a total of approximately ft2 of perforated plate surface area.
- To prevent the potential for plugging and creating a hold-up volume, the refueling cavity drain covers are removed during modes requiring operability. This assures that water which is routed into refueling cavity will drain into the ECCS sump thus increasing sump level.
- interceptors are installed inside containment both Units 1 and 2. No is taken in the analysis for the resulting reduced debris transport.
- high head branch flow line orifices were installed and the associated throttle valves were changed to ensure that adequate in the valve will prevent debris from plugging.
- Completed latent debris sampling and characterization, including other debris sources, labels,
- Completed debris generation debris transport analyses.
- Completed VH~'SHI downstream effects analysis.
-3 to NL-13-0954 Path Forward and Schedule for Resolution of 91
- Completed net positive suction head (NPSH) analysis.
- Procedural and program controls are in place to ensure materials used in the containments will not result in an increase of the debris loading beyond the analyzed values. This includes controls for containment coatings, and insulation.
The following provides a summary description of the margins and conservatisms associated with the resolution actions taken to date. margins and conservatisms provide support for the extension of required to address GL 2004-02 for FNP, Units 1 and
- Detailed analyses of debris generation and transport ensure that a bounding quantity a limiting mix of debris are assumed at the containment sump screen following a design basis accident (DBA). Using the results of analyses, conservative evaluations were performed to determine worst-case screen head loss. Other conservatisms were applied to ensure that net positive suction head (NPSH) margins were conservatively calculated and conservative testing was done to demonstrate that vortexing and air ingestion would not occur.
The following is a list of significant conservatisms in FNP ECCS sump design, testing and analysis. It is provided to demonstrate that a conservative holistic approach for the resolution of GSI-191 is in effect FNP.
- Debris interceptors are installed in both FNP Units 1 and 2 containments. No credit is taken in either the or testing for debris captured by these interceptors.
interceptors are located in debris flow path between the large-break loss-ot-coolant accident (LBLOCA) zone of influence and the ECCS sump screens in the secondary shield wall access pOints. While the amount of debris intercepted by these interceptors is not quantified, they provide defense-In-depth.
- No credit was taken for near field debris settling. arrangement for FNP was highly stirred using multiple mechanical mixers along with test facility flow to lift the debris and chemical surrogates to extent practicable so that maximum amount practicable is upon screens. As sump has many quiescent areas, it is reasonable to expect that significant settling of coating debris would occur following an LOCA scenario, and much less debris would transport and lift upon the screens than tested.
- FNP has separate sump screens for each RHA and containment spray (CS) pump. There are a total of four screens in unit. Screen testing was done with the assumption that only one train of RHR and CS operate (2 of 4 screens), thus, doubling amount of debris loading to each screen as compared to all four pumps operating.
to NL-13-0954 Path Forward and Schedule for Resolution of GSI-191 Assuming only one of the four pumps failed to operate would reduce the amount of debris deposited on each screen to approximately 2/3 of the values.
/II To generate the total debris loading for the screens, the debris quantity for the limiting break location that generated the most coatings debris is combined with the debris quantity from one location that the most insulation debris. In reality, are two separate break locations that cannot occur simultaneously. Thus, the tested debris loading for the screens is maximized.
/II FNP assumed that all failures of acceptable coating in the ZOI were as chips.
FNP is a low fiber plant, this is more conservative than the assumption that coating failed as particulates. FNP specific testing demonstrated that chips increase head loss more than particulates for the (very low fiber) debris loading.
/II Nonqualified containment coatings are ali assumed to fail. Electric Power Research Institute (EPRI) report, "Design Accident Testing of Pressurized Water Reactor Unqualified Original Equipment Manufacturer Coatings," for original equipment manufacturer (OEM) coating failures documented testing on various types of unqualified coatings, alkyds, epoxies and inorganic zinc. A 100% failure of aU unqualified coatings is conservative, since EPRI report indicated that only about 20% of unqualified OEM coatings actually detached as a result of autoclave DBA testing.
/II The head loss associated with the Reflective Metal Insulation (AMI) transported to the sump was treated as separate from the head with the other debris. This is considered conservative, as a mixed debris bed containing AMI would be expected to have a lower head loss.
/II All debris is assumed to be present the sump screens immediately upon initiation of AHA recirculation. No credit was taken for time to transport while sump continues to fill, due to continued addition of water to the sump resulting from containment spray operation.
/II For testing purposes, twice the inventoried quantity of unqualified labels was to detach and transport to the sump screens. In reality, many of the are tightly adhered and many are protected from direct containment spray and likely would remain in place. In the event of detachment, many of labels would not transported to the sump screens due to torturous paths between the labels and the screens.
/II Two hundred pounds of latent was assumed for testing purposes wrlile surveyed value was 125 pounds. In addition, the debris was assumed to be 15% fiber NEI guidance, although the source of fiber in the FNP containment is very limited as FI\IP is primarily a RMI insulation plant. Very limited amounts of fibrous insulation are installed on the steam generator instrument lines and around the reactor nozzle penetrations. All latent fiber in containment and other fiber within the break ZOI are assumed to transport to the sump screens.
/II Measured tested screen head losses were increased by 43% to account for uncertainties. conservatively increased head loss values were used NPSH margins.
E1 to NL-13-0954 Path Forward and Schedule for Resolution of GSI-191
- FNP does not credit containment pressure above pre-accident pressure for net positive suction head available (NPSHa) calculations. In reality. post LOCA pressures in containment would provide significant NPSH margin above calculated values. Analysis shows this would add a minimum 16 feet of NPSHa immediately upon initiation of recirculation and would increase during the event.
- A very detailed and conservative calculation is used to determine minimum sump level. The containment sump level calculations were performed using "stacked" conservatisms. For example, maximum reduction in Refueling Water Storage Tank (RWST) mass due to level instrument uncertainty was assumed even thought this would involve opposing instrument uncertainties; positive on the high end of the instrument range and negative on the low end of the In addition, minimum allowable initial water volumes were assumed for both the accumulators and the RWST. Also, switch over to recirculation is assumed to occur instantaneously at the RWST low level set points. Operator action time is for the operator to manually perform swap over from injection to recirculation mode. During this time, additional inventory is added to the ECCS sump. A realistic value for containment sump level would at least 6 inches higher than used for NPSH calculations.
- Testing for FNP's screens was conducted at lower than minimum sump In addition, maximum ECCS pump flows were used for these These tests clearly demonstrated that FNP screens are not susceptible to ingestion under worst case LBLOCA or small-break loss-of-coolant accident (SBLOCA) conditions.
The following describes the plant specific design features and procedural capabilities that exist detecting and mitigating a strainer blockage or fuel blockage condition:
- Training on monitoring of indications of and responses to sump clogging; enhancement of ECCS logs to provide additional detail concerning the recognition and response to sump suction screen fouling; new training materials and job performance measures addressing the need for long-term monitoring of the recirculation phase; how to recognize sump blockage is taking place; and actions to be taken if blockage is encounte red.
- Guidance reduce depletion of the RWST and initiate makeup to the RWST from normal and alternate sources during efforts to restore normal ECCS flowpaths.
- Containment exit inspections with logged material accounting procedures, and comparable controls for emergency entries into containment; and post-outage recirculation sump cleanliness and material control procedures to ensure sumps are free of debris (trash, protective clothing. etc).
- Post-refueling and heat-up procedures to inspect cavity drains are properly restored with their blind flanges and drain covers removed.
to NL-13-0954 Path Forward and Schedule for Resolution of GSI-191
- Inspections to ensure subsystem inlets are not restricted by debris and sump components (trash racks, screens, etc.) show no evidence of abnormal corrosion or structural distress, and that the sump screens are correctly configured.
Additionally, the following actions have been implemented to provide further Defense in Depth
- SNC completed the installation of new sump on Units 1 and 2. These strainers have increased the available surface area to with debris in the recirculation water.
Although these measures are not expected to be required based on the very low probability of an event would challenge either the capability of the strainer to provide necessary flow to the and systems, or result in significant quantities of debris being transported to the reactor vessel that would inhibit the necessary cooling fuel, they do provide additional assurance that health and safety of the public would be maintained. These measures provide support for the extension of time required to completely address 2004-02 for Units 1 and 2.
In addition to the in depth measures listed above, SNC is currently evaluating the recommendations made by Westinghouse in DW-12-01 and will also evaluate any other recommendations made for mitigative After evaluations are complete, revisions to or Operations training will be made if necessary.
Conclusion SNC expects that the GSI-191 resolution path for FNP, Units 1 and 2 is acceptable, based on the information provided in this document. The execution of the actions identified in this document will result in successful resolution of GSI-191 and closure of GL 2004-02.
References
- 1. SNC letter NL-08-0551 from L. M. Stinson to NRC, "Joseph M. Nuclear Plant Final Supplemental Response to NRC Generic Letter 2004-02," April 2008 (ADAMS Accession No. ML081210452)
SNC letter NL-08-2173 from H. Jones to "IRC, "Joseph M. Farley Nuclear Plant Supplemental Response to NRC Generic 2004-02," February 28, 2008 (ADAMS Accession No. ML080660657)
- 3. SNC letter I\IL-09-0982 from M. J. Ajluni to NRC, "Joseph M. Farley Nuclear Plant Response to for Additional Information Regarding NRC Generic Letter 2004*
"July 27,2009 (ADAMS Accession No. ML092380647)
- 4. SNC letter from L. M. Stinson to NRC, "Joseph M. Farley Nuclear Plant Units 1 and 2 Generic Letter 2004-02 Response to Extension Request - Chemical Effects," December 7, 2007.
- 5. SNC letter NL-07-0892 from L. M. Stinson to NRC, "Joseph M. Farley Nuclear Plant Units 1 and 2 Extension Request for Completion of Corrective Actions Associated with Generic Letter 2004-02," July 3,2007.
E1-7
M. Farley Nuclear Plant Proposed Path to Closure of Generic Safety Issue 91,"Assessment of Debris Accumulation on Pressurized-Water Reactor Sump Performance" Enclosure 2 List of Regulatory Commitments to NL-13-0954 List of Regulatory Commitments List of Regulatory Commitments The following table identifies the regulatory commitments in this document. Any other statements in this submittal represent intended or planned actions. Such statements are provided for information purposes and are not considered to be regulatory commitments.
Commitment SNC will submit a final updated supplemental Within response to support of GL 2004-02 for Unit 1 & 2 If SNC determines that proposed testing or analysis resolution path will not viable, an alternate resolution path will discussed with the NRC to gain acceptance of the proposed path to establish an ac(:eptable com letion schedule SNC will update current licensing Within 18 months following NRC acceptance (UFSAR) and complete the identified removal of the updated supplemental response or modification of insulation debris sources in FNP, Units 1 and 2 containment per plant modification procedures rocesses 10 CFR e