ML13136A047

Proposed Resolution Path for Closure of Generic Letter (GL) 2004-02 and Generic Safety Issue (GSI) 191, Pressurized Water Reactor Sump Performance

ML13136A047
Person / Time
Site:	Fort Calhoun
Issue date:	05/15/2013
From:	Cortopassi L Omaha Public Power District
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
GL-04-002, GSI-191, LIC-13-0058
Download: ML13136A047 (10)

Text

Employment with Equal Opportunity 444 South 16th Street Mall Omaha, NE 68102-2247 LIC-13-0058 May 15, 2013 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001

References:

Docket No. 50-285 (See Reference List on Page 3)

SUBJECT:

Proposed Resolution Path for Closure of Generic Letter (GL) 2004-02 and Generic Safety Issue (GSI) 191, Pressurized Water Reactor Sump Performance at Fort Calhoun Station Unit No. 1 The Omaha Public Power District (OPPD) provides the proposed resolution path for closure of Generic Letter 2004-02, Potential lmpact of Debris Blockage on Emergency Recirculation during Design Basis Accidents at Pressurized-Water Reactors (Reference 2) and Generic Safety Issue (GSI) 191, Assessment of Debris Accumulation on Pressurized-Water Reactor Sump Performance, at Fort Calhoun Station (FCS) Unit No. 1, in Enclosure 1.

In Reference 16, the Nuclear Energy Institute (NEI) highlighted the current industry status and recommended actions for closure of GSI-191 which were based on licensees providing a docketed submittal to the Nuclear Regulatory Commission (NRC) by December 31, 2012, that would outline a GSI-191 resolution path and schedule pursuant to the Commission direction (Reference 14). By Reference 19, NEI recommended to the NRC that licensees delay submittal of a GSI-191 resolution path and schedule until January 31, 2013, or 30 days following placement of both the Commissions response to Reference 17 and the NRC staffs safety evaluation (SE) for topical report WCAP-16793-NP, Revision 2 (Reference 15) on the public record. In Reference 21, the Commission approved the staffs recommendation in Reference 17 to allow licensees the flexibility to choose any of the three (3) 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 NRCs SE (Reference 22) for the WCAP (Reference 15) was made publicly available by the 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.

U. S. Nuclear Regulatory Commission LIC-13-0058 Page 2 of 4 The NEI template was used for the development of Enclosure 1 for Fort Calhoun Station, Unit No.1, 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. contains the commitment table identifying those actions delineated by OPPD in as regulatory commitments which are being tracked by action request AR 59106.

Any other actions discussed in this submittal represent intended or planned actions by OPPD, and as such are provided for information and are not regulatory commitments.

In accordance with 10 CFR 50.91, a copy of this submittal is being provided to the designated State of Nebraska official.

If you should have any questions regarding this submittal or require additional information, please contact the Supervisor - Nuclear Licensing, Mr. Bill R. Hansher at 402-533-6894.

I declare under penalty of perjury that the foregoing is true and correct.

Louis P. Cortopassi Site Vice President and CNO LPC/RWS/JKG/CO/dll

Enclosures:

1. Fort Calhoun Station, Unit No. 1 Resolution Path for Closure of Generic Letter (GL) 2004-02 and Generic Issue (GSI) 191, Pressurized Water Reactor Sump Performance

2. Regulatory Commitments c:

A. T. Howell, NRC Regional Administrator, Region IV L. E. Wilkins, NRC Project Manager J. M. Sebrosky, NRC Project Manager J. C. Kirkland, NRC Senior Resident Inspector Manager Radiation Control Program, Nebraska Health & Human Services, R & L Public Health Assurance, State of Nebraska

U. S. Nuclear Regulatory Commission LIC-13-0058 Page 3 of 4 Reference List

1.

Docket No. 50-285

2.

Letter from NRC (B. A. Boger), Generic Letter (GL) 2004-02, Potential lmpact of Debris Blockage on Emergency Recirculation during Design Basis Accidents at Pressurized-Water Reactors," dated September 13, 2004 (NRC-04-0115) (ML042360586)

3.

Letter from OPPD (R. L. Phelps) to NRC (Document Control Desk), "90-Day Response to Generic Letter 2004-02, Potential lmpact of Debris Blockage on Emergency Recirculation during Design Basis Accidents at Pressurized-Water Reactors," dated March 4, 2005 (LIC-05-0017) (ML050630538)

4.

Letter from OPPD (H. J. Faulhaber) to NRC (Document Control Desk), "Follow-Up Response to Generic Letter 2004-02, Potential lmpact of Debris Blockage on Emergency Recirculation during Design Basis Accidents at Pressurized-Water Reactors," dated August 31, 2005 (LIC-05-0101) (ML053070109)

5.

Letter from OPPD (H. J. Faulhaber) to NRC (Document Control Desk), "Request for Extension to the Completion Date for Corrective Actions taken in Response to Generic Letter 2004-02, Potential lmpact of Debris Blockage on Emergency Recirculation During Design Basis Accidents at Pressurized-Water Reactors and lnformation Regarding Actions taken as a Result of lnformation Notice 2005-26," dated November 18, 2005 (LIC 0131)

6.

Letter from OPPD (H. J. Faulhaber) to NRC (Document Control Desk), "Revised Request for an Extension to the Completion Date for Corrective Actions taken in Response to Generic Letter 2004-02," dated June 9, 2006 (LIC-06-0067)

7.

Letter from NRC (C. Haney) to OPPD (R. T. Ridenoure), "Fort Calhoun Station Unit No. 1 -

Generic Letter 2004-02, Potential lmpact of Debris Blockage on Emergency Recirculation during Design Basis Accidents at Pressurized Water Reactors, Extension Request Approval (TAC No. MD2323)," dated August 11, 2006 (NRC-06-0103)

8.

Letter from OPPD (D. J. Bannister) to NRC (Document Control Desk), "Fort Calhoun Station Unit No. 1 License Amendment Request (LAR), Modification of the Containment Spray System Actuation Logic," dated July 30, 2007, (LIC-07-0052) (ML072150293)

9.

Letter from OPPD (R. P. Clemens) to NRC (Document Control Desk), Fort Calhoun, Unit 1 - Supplemental Response to Generic Letter 2004-02, Potential Impact of Debris Blockage on Emergency Recirculation during Design Basis Accidents in Pressurized-Water Reactors, dated February 29, 2008 (LIC-08-0021) (ML082960244)

10. Letter from NRC (M. T. Markley) to OPPD (D. J. Bannister), "Issuance of Amendment Re:

Modification of Containment Spray System Actuation Logic and Dampers in Containment Air Cooling and Filtering System (TAC Nos. MD6204 and MD7043)," dated May 2, 2008 (NRC-08-0049)

11. Email from NRC (M. T. Markley) to OPPD (B. R. Hansher), Request for Additional Information, Fort Calhoun Station, Unit 1 - Supplemental Response to Generic Letter (GL) 2004-02 (TAC No. MC4686), dated July 28, 2008

12. Letter from OPPD (J. A. Reinhart) to NRC (Document Control Desk), Fort Calhoun, Unit 1

- Notice of Completion of Corrective Actions taken in Response to Generic Letter 2004-02 and Response to Request for Additional Information (RAI) for Fort Calhoun Station (FCS)

Unit No. 1, dated October 16, 2008 (LIC-08-0107) (ML082960244)

13. Summary of Teleconference Meeting with Omaha Public Power District to Discuss NRC Staff Request for Additional Information dated February 12, 2010 on Generic Letter 2004-02 for Fort Calhoun Station, Unit 1 (TAC No. MC4686), dated June 30, 2010 (ML101940301)

U. S. Nuclear Regulatory Commission LIC-13-0058 Page 4 of 4 Reference List (continued)

14. Staff Requirements - SECY-10-0113 - Closure Options for Generic Safety Issue - 191, Assessment of Debris Accumulation on Pressurized-Water Reactor Sump Performance, dated December 23, 2010

15. 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, dated October 12, 2011

16. Letter from NEI (John C. Butler) to NRC (William H. Ruland), GSI-191 - Current Status and Recommended Actions for Closure, dated May 4, 2012 (ML12142A316)

17. SECY-12-0093, Closure Options for Generic Safety Issue - 191, Assessment of Debris Accumulation on Pressurized-Water Reactor Sump Performance, dated July 9, 2012 (ML121310648)

18. Letter from NextEra Energy to NRC (Document Control Desk), Strainer Fiber Bypass Test Protocol, dated August 10, 2012 (ML12228A330)

19. Letter from NEI (John C. Butler) to NRC (William H. Ruland), GSI-191 - Revised Schedule for Licensee Submittal of Resolution Path, dated November 15, 2012 (ML12325A072)

20. Letter from NRC (William H. Ruland) to NEI (John C. Butler), Nuclear Regulatory Commission Review of Generic Safety Issue - 191 Nuclear Energy Institute Revised Schedule for Licensee Submittal of Resolution Path, dated November 21, 2012 (ML12326A497)

21. SRM-SECY-12-0093 - Closure Options for Generic Safety Issue-191, Assessment of Debris Accumulation on Pressurized-Water Reactor Sump Performance, dated December 14, 2012 (ML12349A378)

22. 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, dated April 8, 2013

23. Letter from OPPD (R. P. Clemens) to NRC (Document Control Desk), Fort Calhoun Station Unit No. 1, 60 Day Response to NRC Bulletin 2003-01, Potential Impact of Debris Blockage on Emergency Sump Recirculation at Pressurized-Water Reactors, dated August 8, 2003 (LIC-03-0105) (ML032240032)

24. Letter from OPPD (R. L. Phelps) to NRC (Document Control Desk), Response to Requests for Additional Information on the Fort Calhoun Station Unit No. 1 Response to NRC Bulletin 2003-01, Potential Impact of Debris Blockage on Emergency Sump Recirculation at Pressurized-Water Reactors, " dated June 11, 2004 (LIC-04-0072)

(ML041670407)

LIC-13-0058 Page 1 of 5 Fort Calhoun Station, Unit No. 1 Resolution Path for Closure of Generic Letter (GL) 2004-02 and Generic Issue (GSI) 191, Pressurized Water Reactor Sump Performance

=

Background===

The Omaha Public Power District (OPPD) submitted documentation for closure of Generic Letter (GL) 2004-02 in Reference 12. Following this submittal, exchanges of requests for additional information (RAIs) and responses to these RAIs occurred with the last docketed exchange documented in Reference 13. OPPD informally submitted revised responses on October 1, 2010, as discussed in Reference 13. No further exchanges concerning closure of GL 2004-02 have occurred between OPPD and the NRC, pending issuance of the safety evaluation report (SER) for topical report WCAP-16793-NP (Reference 15).

Industry recommended actions for closure of Generic Safety Issue (GSI) 191, PWR Sump Performance, were identified in Reference 16. The key elements of this plan were reflected in the closure options discussed in SECY 12-0093 (Reference 17). As part of this plan, licensees of Pressurized Water Reactors (PWRs) would have provided a docketed submittal to the NRC by December 31, 2012, that outlines a GSI-191 resolution path and schedule for each of their PWRs. NEI recommended that licensees delay submittal of their GSI-191 resolution path and schedule until January 31, 2013, or 30 days following placement of both documents into the public record, whichever is later, in Reference 19. The NRC concurred with this recommendation in Reference 20.

Selection of Option Based on the information provided in References 17 and 21, OPPD has selected the deterministic prong of Option 2 and intends to pursue refinements to evaluation methods and acceptance criteria. To support use of this path, and continued operation for the period required to complete the necessary analysis and testing, OPPD has evaluated the design and procedural capabilities that exist to identify and mitigate sump strainer and in-vessel blockage. A description of these detection and mitigation measures is provided later in this document.

Additionally, a summary of the existing margins and conservatisms that exist for Fort Calhoun Station (FCS) is also included in this document.

Characterization of Current Containment Fiber Status From the debris generation and debris transport analysis, OPPD has determined that 26.8 cubic feet (ft3) (4,342 pounds-mass (lbm) based on a micro density of TempMat material of 162 lbm/ft3) of fibrous debris could be transported to the strainers, as documented in Reference 9.

Based on previously performed strainer bypass testing, the total quantity of fiber calculated to bypass the strainer is 5.52 lbm. This equates to an approximate value of 19 grams/fuel assembly (g/FA). Bypass testing was conducted with TempMat, which was deemed to be representative of the types of fibrous insulation in use at FCS, which include: TempMat, NukonTM, Cerafiber and Fiberglass. OPPD intends to re-perform this testing utilizing a test approach similar to that currently being utilized by other licensees (Reference 18). The results of this testing will then ultimately establish the quantity of fiber that will be allowed to be transported to the reactor fuel.

LIC-13-0058 Page 2 of 5 Characterization of Strainer Head Loss Status OPPD previously provided the results of strainer head loss testing, including the impact of chemical effects, in References 9, 12, and 13. The results of this testing demonstrated acceptable results with regard to allowable head loss. OPPD intends to re-perform strainer head loss testing based on lessons learned with regard to strainer testing methodology including determination of chemical effects impact (production, time-dependency, etc.) to improve the margin associated with this aspect of GL 2004-02.

Characterization of In-Vessel Effects OPPD intends to follow the resolution strategy proposed by the PWROG for establishing in-vessel debris limits for the type of plant design that exists at FCS.

Licensing Basis Commitments OPPD currently has a commitment to evaluate the final conditions issued by the NRC in regards to WCAP-16793-NP (and how it applies to FCS) and provide a formal response as a separate submittal on the resolution of the in-vessel downstream effects issue within 90 days of issuance of a final NRC staff SE on this matter. [This commitment is being tracked by action requests AR 35967 and AR 55548 for completion.]

As a result of the remaining open questions associated with GL 2004-02 for FCS and the information contained within this document, the previously established commitments [AR 35967 and AR 55548] are considered to be closed based on the intended direction to be taken as described in this document. New regulatory commitments as a result of this document are described in Enclosure 2. [Action request AR 59106 will track completion of these regulatory commitments.]

Resolution Schedule NOTE: There is the potential for misalignment between the expected completion dates within the SECY and the PWROGs schedule for establishing in-vessel debris limits. Depending on when the first refueling outage (RFO) is after January 1, 2013, and the length of the outage, the PWROG proposed resolution timeline may not provide the information necessary to plan for, and then remove/remediate insulation within the three (3) RFOs following January 1, 2013. This may require OPPD management to meet with the NRC to establish an acceptable resolution schedule.

OPPD is planning to achieve closure of GSI-191 and address GL 2004-02 per the following schedule:

Complete measurements for insulation replacement and remediation by the end of the first RFO following January 1, 2013; currently expected to be completed during the fall of 2014.

Strainer head loss and fiber bypass testing is expected to be completed by the end of 2015.

Complete the necessary insulation replacements, remediation, or model refinements by the completion of the third RFO following January 1, 2013 (Fall 2017).

LIC-13-0058 Page 3 of 5 Within six months of establishing a final determination of the scope of insulation replacement or remediation, OPPD will submit a final updated supplemental response to support closure of GL 2004-02 for FCS.

OPPD will update the current licensing basis (USAR, etc.) following NRC acceptance of the updated supplemental response for FCS and completion of the identified removal or modification of insulation debris sources in Containment.

However, as stated in Reference 21, this schedule is based on completion and acceptance of the necessary testing by the NRC and may require adjustments if testing results are not available by the end of 2014.

Summary of Actions Completed to Address GL 2004-02 To support closure of GSI-191 and to address GL 2004-02, OPPD has completed the following actions for FCS:

Two new sump strainers with more than 15 times the area of the original sump screens were installed during the 2006 RFO. The new strainers have a combined area of 1032 ft2 vs. the previous area of 56 ft2 and a total flow area of approximately 250 ft2 vs. the 33.6 ft2 area of the previously installed strainers.

During the 2006 RFO, a significant amount of CalSil and fibrous insulation was replaced with reflective metallic insulation (RMI) during the steam generator (SG), pressurizer (PZR),

and reactor pressure vessel (RPV) head replacement projects. Specifically, 56% CalSil and 75% TempMat from the 2003 configuration were replaced with RMI. In addition, 7041 ft2 of unqualified coatings were removed during the same RFO.

Trisodium phosphate (TSP), the previous Containment sump buffer, was replaced with sodium tetraborate (NaTB) to reduce formation of chemical precipitates.

OPPD requested and received approval for a license amendment to eliminate automatic start of the containment spray (CS) pumps during a loss-of-coolant-accident (LOCA)

(References 8 and 10, respectively). This change, which significantly reduces debris transport and lowers flow rates through the sump strainer screens, was implemented during the 2008 RFO. This also allows a longer core injection period prior to recirculation and a reduction in material transported to the sump strainers.

The Debris Generation Debris Transport and the ex-vessel downstream long term effects analyses were completed. The Downstream Effects Analysis identified the potential plugging of the high pressure safety injection (HPSI) cyclone separators.

The cyclone separators on the HPSI seal cooler lines were replaced with new cyclone separators. The new cyclone separators were tested to ensure that they would not plug with debris representative of the strainer effluent.

Programmatic controls were developed for controlling insulation replacements in Containment as well as for latent debris sampling and Containment cleanliness.

Net positive suction head (NPSH) analysis and strainer testing were completed to verify that the head loss across a fully loaded strainer does not exceed the available NPSH margin.

LIC-13-0058 Page 4 of 5 Summary of Margins and Conservatisms for Completed Actions for GL 2004-02 The following provides a summary description of the margins and conservatisms associated with the resolution actions taken to date. These margins and conservatisms provide support for the extension of time required to address GL 2004-02 for FCS.

The computational fluid dynamics (CFD) analyses were performed assuming flow from three HPSI pumps. Physical modifications to the plant and changes to the plant's operating procedures restrict operation to a maximum of two HPSI pumps. This results in a conservative calculation of the amount of debris transported to the vicinity of the strainer.

The CFD analyses were performed with a conservatively low water volume in Containment.

The CFD analyses conservatively assumed water hold-up in the reactor cavity and at higher levels in the Containment. In reality, after implementation of the Water Management Strategy Project, CS is no longer actuated and the water volume in Containment could be ~

6000 ft3 higher than assumed in the analyses.

Strainer testing was conducted using bounding conditions such as minimum water level in Containment, the maximum debris load, the maximum flow through the strainer and the minimum available NPSH margin even though the actual pump alignments in a post-LOCA condition would preclude such a condition.

The Chemical Effects generation calculation and subsequently the strainer testing contain a significant number of conservative assumptions. The calculation assumed maximum pool volume and it is assumed that the pool is not mixed, thus maximizing the amount of precipitates. In addition, one of the largest sources of aluminum in Containment (the nuclear detector cooler fins), was eliminated during the 2011 RFO, when the nuclear detector well cooler coils were replaced and the new coils have copper instead of aluminum fins. This represents a reduction of approximately 2200 ft2 in aluminum surface area since the calculation was performed.

Available NPSH was calculated using the highest sump temperature, lowest NPSH margin for multiple pre-and post-RAS pump alignments and assuming that the head loss across the strainer was at the maximum design limit. The "best estimate" highest head loss across the strainer shows 1.5 feet margin.

Summary of Defense-In-Depth (DID) Measures The following describes the plant specific design features and procedural capabilities that exist for detecting and mitigating a strainer blockage or fuel blockage condition.

Strainer Blockage FCS has, within its Emergency Operating Procedures (EOPs) framework, specific steps for monitoring for indications of sump strainer blockage and actions to be taken if this condition occurs. These actions were described in References 23 and 24, OPPDs response to NRC Bulletin 2003-01 and OPPDs subsequent responses to the NRCs RAIs on Bulletin 2003-01, respectively. These actions taken in response to Bulletin 2003-01, Potential Impact of Debris Blockage on Emergency Sump Recirculation at Pressurized Water Reactors, are still in effect and are contained in the EOPs for LOCA and Functional Recovery.

LIC-13-0058 Page 5 of 5 Fuel (Core) Blockage Detection Multiple methods exist for detection of a core blockage condition as manifested by an inadequate reactor coolant system (RCS) inventory or RCS and core heat removal condition.

The primary methods include core exit thermocouples (CET) and reactor vessel level monitoring system (RVLMS). This monitoring is initiated early in the event in the EOPs through the Safety Function Status Checks which is performed at approximately 10-minute intervals. Emergency response personnel in the Technical Support Center (TSC) will also maintain oversight of plant status through review of Emergency Response Facility Computer System (ERFCS) which includes both CET and RVLMS data. An additional method for detection of a core blockage condition includes monitoring of Containment radiation levels by the TSC staff and/or if an alarm setpoint is reached resulting in an alarm in the control room.

Mitigation Upon identification of an inadequate RCS inventory or core heat removal condition, the EOPs direct the operators to take actions to restore cooling flow to the RCS including:

Reducing HPSI flow rate to only match decay heat requirements.

Refill the Safety Injection Refueling Water Storage Tank (SIRWT).

Attempt to provide core cooling by steaming through the steam generators.

The operators are instructed to contact the TSC for additional guidance as necessary. The TSC will provide assistance in ensuring core heat removal by other means such as:

Use charging pumps to inject borated water into the RCS.

Raise Containment water level to above the hot leg elevation to enable shutdown cooling initiation.

Recommend alternate system alignments for make-up water to the demineralized water (DW) system, if the normal path of the DW system is not available.

Recommend alternate system alignments and flow paths to inject water in the RCS or to refill the SIRWT.

Although these measures are not expected to be required based on the very low probability of an event that would challenge either the capability of the strainer to provide the necessary flow to the Emergency Core Cooling and CS systems, or result in significant quantities of debris being transported to the reactor vessel that would inhibit the necessary cooling of the fuel, they do provide additional assurance that the health and safety of the public would be maintained.

These measures provide support for the extension of time required to completely address GL 2004-02 for FCS.

Conclusion Based on the information provided in this document, OPPD considers the GSI-191 resolution path for FCS acceptable. The execution of the actions identified in this document will result in successful resolution of GSI-191 and closure of GL 2004-02.

LIC-13-0058 Page 1 of 1 Regulatory Commitments The following table identifies those actions committed to the NRC by OPPD in this letter for FCS. Any other actions discussed in this letter represent intended or planned actions by OPPD. They are described to the NRC for information purposes and are not regulatory commitments.

Commitment 1 Date 2 Complete measurements for insulation replacement and remediation by the end of the first RFO following January 1, 2013; currently expected to be completed during the fall of 2014. [AR 59106]

By the end of Fall 2014 RFO Strainer head loss and fiber bypass testing is expected to be completed by the end of 2015. [AR 59106]

December 31, 2015 Complete the necessary insulation replacements, remediation, or model refinements by the completion of the third refueling outage (RFO) following January 1, 2013 (Fall 2017). [AR 59106]

By the end of Fall 2017 RFO Within six months of establishing a final determination of the scope of insulation replacement or remediation, OPPD will submit a final updated supplemental response to support closure of GL 2004-02 for FCS. [AR 59106]

Within six months following Fall 2014 RFO OPPD will update the current licensing basis (USAR, etc.) following NRC acceptance of the updated supplemental response for FCS and completion of the identified removal or modification of insulation debris sources in Containment. [AR 59106]

By the end of Fall 2017 RFO 1 This schedule for these commitment actions is based on completion and acceptance of the necessary testing by the NRC and may require adjustments if testing results are not available by the end of 2014.

2 FCS is currently in Mode 5 and future RFO schedules will be based on plant restart; therefore, these commitment dates are based on current expected RFO dates.