ULNRC-05989, Path Forward for Resolution of GSI-191

Path Forward for Resolution of GSI-191

ML13136A290
Person / Time
Site:	Callaway
Issue date:	05/16/2013
From:	Reasoner C Ameren Missouri
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
ULNRC-05989
Download: ML13136A290 (14)

Text

Cleve Reasoner

~~ Vice President Engineering WAmeren Ameren Missouri Callaway Plant T 573.676.8241 MISSOURI F 573.676.4056 May 16,2013 ULNRC-05989 U.S. Nuclear Regulatory Cmntnission Attn: Docmnent Control Desk Washington, DC 20555-0001 10 CFR 50.54(f)

Ladies and Gentlemen:

DOCKET NUMBER 50-483 CALLAWAY PLANT UNIT 1 UNION ELECTRIC CO.

FACILITY OPERATING LICENSE NPF-30 PATH FORWARD FOR RESOLUTION OF GSI-191 Union Electric (db a Ameren Missouri) hereby submits the enclosed document which describes the plan for Callaway Plant to reach closure of the regulatory requirements of NRC Generic Letter 2004-02, "Potential Impact of Debris Blockage on Emergency Recirculation During Design Basis Accidents at Pressurized-Water Reactors," in regard to the issues raised by Generic Safety Issue (GSI) I9I, "Assessment of Debris Accumulation on Pressurized-Water Reactor Sump Performance."

The Nuclear Regulatory Commission and the staff have provided guidance to licensees on acceptable paths to closure of GSI -I9I, including the issuance of SECY -I2-0093 (Reference 5 of Attachment I) and Staff Requirements Memorandum (SRM)-SECY -I2-0093 (Reference 8 of Attachment I). In addition, the Nuclear Energy Institute (NEI) has worked with the NRC staff to develop the schedule and the content of licensee's submittals on paths to closure, as addressed in letters dated May 4, 20I2, November I5, 20I2 and November 2I, 20I2 (References 4, 6, and 7 of Attachment I). Following this guidance, and upon issuance of the NRC's Final Safety Evaluation (Reference 9 of Attachment I), for the Pressurized Water Reactor Owners Group topical report WCAP-I6793-NP, revision 2, "Evaluation of Long-term Cooling Considering Particulate Fibrous and Chemical Debris in the Recirculating Fluid" (Reference 3 of Attachment I), Ameren Missouri is subtnitting the enclosure to this letter, i.e.,

"Callaway Plant Closure Option for Generic Safety Issue I9I (GSI-I9I), Assessment of Debris Accumulation on Pressurized Water Reactor Sump Perfonnance." The proposed path to closure, as described in the enclosure, corresponds to Option 2b, "Full Risk-Informed Resolution Path," of SECY -I2-0093.

PO Box 620, MC CA-460 Fulton, MD 65251 AmerenMissouri.com

U LN RC-059X<)

May 16, 2013 Page 2 of4 Attachn1ent 2 contains the regulatory commitments associated with this response. These are intended to facilitate closure ofGSI-191 and address GL 2004-02 in accordance with the required resolution schedule.

If you have any questions concerning the content of this letter, please contact Scott Maglio, Regulatory Affairs Manager, at 573-676-8719.

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

Sincerely, Executed on:

Cleveland 0. Reasoner Vice President, Engineering DRB/nls : List of References : List of Comtnitments : Callaway Plant Closure Options for Generic Safety Issue 191 (GSI-191 ), Assesstnent of Debris Accumulation on Pressurized Water Reactor Sump Performance.

lJ LNRC-059X9 May I (), 20 I 3 Page 3 of4 cc: Mr. Arthur T. I-I owe! I Regional Adn1inistrator U.S. Nuclear Regulatory Commission Region IV 1600 East Latnar Boulevard Arlington, TX 76011-451 I Senior Resident Inspector Callaway Resident Office U.S. Nuclear Regulatory Commission 8201 NRC Road Steedman, MO 65077 Mr. Fred Lyon Project Manager, Callaway Plant Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Mail Stop 0-8B 1 Washington, DC 20555-2738

U LN RC-059X9 May 16,2013 PagL: 4 of 4 Index and send hardcopy to QA File A160.0761 Hardcopy:

Certrec Corporation 4150 International Plaza Suite 820 Fort Worth, TX 76109 (Certrec receives ALL attachments as long as they are non-safeguards and may be publicly disclosed.)

Electronic distribution for the following can be made via Responses and Reports ULNRC Distribution:

A. C. Heflin F. M. Diya C. 0. Reasoner III B.L.Cox S. A. Maglio T. B. Elwood L. H. Kanuckel R. Holmes-Bobo NSRB Secretary STARS Regulatory Affairs Mr. John O'Neill (Pillsbury Winthrop Shaw Pittman LLP)

Attachment I to UI,N RC-059R9 Page I of I ATTACHMENT I List of References The following docmnents are referred to in this letter:

I. 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 Sutnp 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."

Attachn1ent 2 to U LN RC-059X9 Page I of I ATTACHMENT 2 List of Commitments The following table identities those actions cotnmitted to by Atncren Missouri in Enclosure I of this docUJnent. Any other statetnents in this docutncnt are provided for infonnation purposes and are not considered cotntnitments. Please direct questions regarding these cotntnittnents to Scott Maglio at 573-676-8719.

COMMITMENTS Due Date/Event Commitment Number Ameren Missouri will submit the necessary December 31, 2015 50261 request/correspondence (e.g., regulatory exemption request) for resolving GSI-191 at Callaway Plant pursuant to Option 2b (risk-informed approach).

Ameren Missouri will complete all work required for December 31, 2019 50262 final resolution of GSI-191 (i.e., all licensing actions and plant modifications) per the schedule agreed upon between the industry (NEI) and NRC.

to ULNRC-05989 Callaway Plant Closure Option for Generic Safety Issue 191 (GSI-191), Assessment of Debris Accumulation on Pressurized Water Reactor Sump Performance (Ameren Missouri response for Callaway Plant seeking closure of GSI-191 using the Risk-Informed Approach found in SECY-12-0093 Option 2b.)

to ULNRC-05989 Ameren Missouri GSI-191 Solution Callaway Plant Option 2b Introduction Ameren Missouri will pursue Option 2b for Callaway Plant, wherein it has been proposed for moderate to high fiber plants that performing a risk-informed evaluation of the potential for recirculation sump strainer blockage and in-vessel blockage could resolve Generic Safety Issue, GSI-191, as identified in SECY-12-0093.

To support use of this path and continued operation for the period required to complete the necessary analysis and testing, Ameren Missouri has evaluated the design and procedural capabilities that exist to identify and mitigate sump strainer and in-vessel blockage at Callaway Plant. A description of these d(tection and mitigative measures are provided below along with a summary of the existing margins and conservatisms that exist for Callaway Plant.

Option 2b: Full Risk-Informed Resolution Path Characterization of In-Vessel Effects The debris generation and debris transport analysis performed for the Callaway Plant were based on testing that was performed using debris preparation methodology that has subsequently not been accepted by the NRC. Furthermore, the analysis utilized a seven diameter (7D) zone of influence (ZOI) instead of the 17D ZOI which the NRC is reviewing in WCAP-16793, Revision 2. Thus, Callaway Plant is evaluating the amount of fibrous debris which could be transported to the strainers.

The analysis performed to determine the mass of fiber which would pass through the strainer was based on the debris generation using a 7D ZOI. Thus the analysis will be revised. It is conservatively concluded that the Callaway Plant is a medium to high fiber plant, and Ameren Missouri will perform additional testing and analysis commensurate with the amount of fiber located in containment.

The fibrous debris sources considered in this analysis include NUKON Insulation as this was the tested and approved insulation at the time of construction of the Callaway Plant.

This was documented in a letter to Owens-Coming Fiberglass Corporation regarding the Final Staff Evaluation ofTopical Report OCF-1, "Nuclear Containment Insulation System," received December 8, 1978.

The current debris generation, debris transport analysis, strainer head loss testing and by-pass testing for the Callaway Plant will be re-evaluated utilizing a revised test approach that complies with WCAP-16793, Revision 2. The results of this testing will then establish a conservative quantity of fiber that could be transported to the strainers and the reactor fuel. Ameren Missouri will establish plant-specific in-vessel debris limits to support a risk-informed solution for the Callaway Plant.

Page 2 of8 to ULNRC-05989 Ameren Missouri GSI-191 Solution Callaway Plant Option 2b Licensing Basis Commitments Ameren Missouri does not currently have any open commitments within the commitment management system for the Callaway Plant such that additional updates or information needs to be submitted to the NRC regarding Generic Letter, GL 2004-02 outside of this Oath and Affirmation letter which will define the path forward for addressing the issues delineated in GS I-191.

Resolution Schedule Ameren Missouri will achieve closure ofGSI-191 and address GL 2004-02 for the Callaway Plant per the following schedule.

1. Ameren Missouri will meet with the NRC as soon as practical after May 16, 2013, to discuss this proposed resolution path.

2. The Callaway Plant is a medium to high fiber plant, and as such, there may be a need to replace Nukon insulation. Measurements for insulation replacement were completed in Refuel Outage (RF-17), in the spring of 2010. If any additional measurements are required they will be performed in RF-20 in the fall of2014.

3. Ameren Missouri will provide a schedule for completion of the risk-informed resolution path activities by third quarter, 2013. This schedule will identify the key testing that needs to be completed in order to determine the viability of the risk-informed approach. The schedule will include a date for submittal of a licensing document change.

4. Ameren Missouri will coordinate the specific submittal schedule with the NRC in order to successfully close this issue by the third refuel outage (spring 2016) following January 1, 2013.

5. Complete any necessary insulation replacements or remediation, or other identified plant changes during the next refueling outage, following issuance of an Safety Evaluation for the risk-informed resolution licensing document change for the Callaway Plant.

6. Within six months of receipt of the SE for the Callaway Plant, submit a final updated supplemental response to support closure of GL 2004-02 for the Callaway Plant by the end of 2019.

7. If it is determined during the risk-informed process that this option is not viable, Ameren Missouri will follow a deterministic resolution path (Option 2a) or pursue a different regulatory approach for suction strainer and in-vessel effects (Option Page 3 of8 to ULNRC-05989 Ameren Missouri GSl-191 Solution Callaway Plant Option 2b

3) that will be acceptable to the NRC, by the third refueling outage after January I, 2013 (spring 2016).

8. Callaway Ameren Missouri will update the current licensing basis FSAR for the Callaway Plant following receipt of the NRC SE that approves the risk-informed resolution approach and completion of any identified removal or modification of insulation debris sources in containment per plant modification procedures and processes pursuant to 10 CFR 50.7l(e).

9. Ameren Missouri will complete all work required for final resolution if GSI-191 fur the Callaway Plant by the end of 2019.

Summary of Actions Completed For GL 2004-02 To support closure of GSI-191 and to address GL 2004-02, Callaway Plant has completed the following actions:

I. Callaway's original strainers had a simple geometry with a filtering surface area of 400 ft 2 , and with nominal 118 square inch openings. In Refuel-15 (2007) new strainers, designed by Performance Contracting Inc. (PCI), were installed which have a complex geometry with a filtering surface area of 6400 ft 2 , and nominal 0.047 square inch circular openings. The PCI stacked-disk corrugated strainer design is able to passively flush debris off of the perpendicular faces of the stacked-disc using the fluid process, thus clearing the screen and allowing the debris to settle in the recessed area between the stacked discs. This design feature significantly lowers the potential for screen blockage.

2. The Callaway Plant containment flow path has been modified extensively to create a tortuous path for the debris laden water. The intent is that the longer and more torturous the path the more debris will settle out and never reach the containment sump strainers, thus reducing the probability of reaching the core.

The A and D Primary Loop openings to the inner containment structure or biosheild, (openings closest to the containment sump strainers) have perforated metal barriers that are secured in place at the end of each refueling outage. This forces the debris laden water to exit the bioshield through the C and B openings.

The debris-laden water then takes a circuitous route or torturous path to the containment sump strainers, passing around, under and over other equipment which forms holdup locations for debris.

3. Latent debris sampling and characterization is performed during refuel outages to be able to characterize the amount of debris that accumulates over time in the containment building.

Page 4 of8 to ULNRC-05989 Amcren Missouri GSI-191 Solution Callaway Plant Option 2b

4. The completed debris generation and debris transport analyses perfonned for the Callaway Plant was completed in the 2008 time frame, and will thus need to be revised to include the impact of revised methodologies.

5. The ex-vessel downstream effects analysis was completed in the 2008 time frame, and will thus need to be revised to include the impact of revised methodologies.

6. Replacement of the containment sump screens with strainers changed the head loss across the containment sump strainers as analyzed for the recirculation phase of a postulated accident, thus impacting the available net positive suction head (NPSH) for the emergency core cooling system (ECCS) and containment spray (CS) pumps. This impact has been assessed in the calculations for ECCS and CSS pump NPSH but will be reviewed and revised as necessary due to revised methodologies.

7. With regards to programmatic and procedural changes established to maintain an acceptable configuration and protect the established design and licensing basis:

a. Ameren Missouri has implemented changes to programmatic controls for

( 1) design change process procedures, (2) containment entry procedures, and (3) scaffold construction and use procedures to minimize the introduction of additional debris in containment.

b. Ameren Missouri has implemented a containment latent debris assessment program which utilizes swipe sampling to determine the amount of latent debris in the containment building.

c. Housekeeping and foreign materials exclusion procedures have been revised to target containment building cleaning based on the results of the swipe sampling survey.

d. Ameren Missouri has implemented a containment coatings assessment program for monitoring and assessing the containment building interior coatings, including administrative controls on conducting coating examinations, deficiency reporting criteria and documentation requirements.

Summary of Margins and Conservatisms for Completed Actions For GL 2004-02 The following provides a summary description of the margins and conservatisrns associated with the resolution actions taken to date. These margins and conservatisrns provide support for the extension of time required to address GL 2004-02 for Callaway Plant.

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Enclosure 1 to ULNRC-05989 Ameren Missouri GSI-191 Solution Callaway Plant Option 2b T abl e 1 C a II away c onservahsms an dM argms T a bl e Item Conservatism Discussion A value of 200 pounds of latent Actual documented amount of Margin of greater than 130 pounds debris was used in the latent debris in Containment is less of latent debris.

determination of debris generation. than 70 pounds.

A distribution of 85% dirt/dust and This mass fraction is recommended 15% latent fibers is assumed for as a conservative assumption in the latent debris in the Section 3.5.2.3 of the SER of the Containment. NEI 04-07 Vol.2.

All debris not blown to upper Conservatively assumed to flow Some debris will be held up at containment outside the bioshield wall various locations. Therefore, there will be less debris actually reaching the sump.

Transport fraction of fine debris Conservatively assumed to be Some fine debris will settle out generated by break 100% prior to reaching the sump.

Therefore, there will be less fine debris actually reaching the sump.

Assumed that all transportable Conservative assumption Some of the miscellaneous debris miscellaneous debris identified in will either be held up or settle out the debris generation calculation, prior to reaching the sump.

(including tags, labels, etc.) would Therefore, there will be less debris be transported to the sumps during actually reaching the sump.

recirculation.

Assumed all debris blown upward Conservative assumption since Some debris will be held up.

would be subsequently washed some debris is blown up onto Therefore, there will be less debris back down by Containment Spray holdup areas protected from the actually reaching the sump.

flow with the exception of any Containment Spray path.

pieces of fiberglass or RMI debris held up on the grating.

Assumed the debris generated by a This is a conservative assumption Some debris (e.g., latent debris)

SBLOCA blast would not be blown as no credit is taken for holdup of will be held up. Therefore, there into upper Containment. debris in upper containment will be less debris actually because the containment spray reaching the sump.

system is not actuated in a SBLOCA. In addition, the SBLOCA has a correspondingly small ZOI.

With the exception of latent debris Conservative assumption since no Some debris will be held up. Some washed to the sumps and inactive credit is taken for debris remaining debris will settle out. Therefore, cavities during pool fill-up, it was on structures and equipment above there will be less debris actually assumed that all latent debris is in the pool water level. reaching the sump.

lower Containment and would be uniformly distributed in the Containment pool at the beginning of recirculation.

Assumed that large-piece debris Conservative assumption since it Some debris will land in stagnant that is not blown to upper neglects the fact that some debris areas and not be transported to the contairunent would be distributed would be blown or washed to areas sump. Therefore, there will be less between the break location and the farther away from the sump during debris actually reaching the sump.

sumps at the beginning of the blowdown and pool fill-up recirculation. phases.

Page 6 of8 to ULNRC-05989 Ameren Missouri GSI-191 Solution Callaway Plant Option 2b Item Conservatism Discussion Water falling from the RCS breach Conservative assumption since any Some debris will be held up. Some was assumed to do so without impact with structures would debris will settle out. Therefore, encountering any structures before dissipate the momentum of the there will be less debris actually reaching the Containment pool. water and decrease the turbulent reaching the sump.

energy in the pool.

The temperature of the water in the This approach is conservative The actual temperature will SI Accumulators is assumed to be because the density of water normally be considerably lower.

equal to the maximum initial decreases with increasing Therefore, there would be a larger Containment air temperature of temperature. mass of available water in the 120°F. accumulators.

For a break in the RCS loop piping, This is conservative because given This would increase the mass of it is assumed that the vessel, RCS the high temperatures within the water in the sump pool at loop piping and pressurizer surge steam generators and pressurizer switchover.

line are refilled with ECCS and the high temperature in the inventory at ECCS switchover to containment building; it is recirculation. probable that the ECCS inventory will not be drawn into these components until later in the postulated accident.

General Observation: All debris All debris in the recirculation pool, No credit is taken in the water that ends up in the recirculation whether it has settled to the bottom level calculation for the volume of pool takes up volume in the or is suspended, displaces water. debris in the recirculation pool.

recirculation pool. Therefore, the actual post LOCA debris-laden water level would be higher than that calculated, not considering the debris.

Maximum debris would be Break in the Loop "D" area could Conservative transport values. A generated at the "D" loop area, but result in lower bioshield transport break in the "C" loop area would transport was assumed to originate fractions than assumed with an generate less debris.

from the "C" loop area, which is origin in the loop "C" area.

closer to the sumps.

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.

Callaway Plant installed debris barriers as described under the section titled "Summary of Actions Completed to Address GL 2004-02."

Callaway Plant has also implemented changes to Emergency Operating Procedures.

Emergency Operating Procedure ECA-1.1, "Loss of Emergency Coolant Recirculation,"

is entered from Emergency Operating Procedure E-1, "Loss of Reactor or Secondary Coolant," when cold leg recirculation capability cannot be verified; or from Emergency Operating Procedure ES-1.3, "Transfer To Cold Leg Recirculation," when at least one flow path from the sump cannot be established or maintained; or from Emergency Page 7 of8 to ULNRC-05989 Ameren Missouri GSI-191 Solution Callaway Plant Option 2b Operating Procedure ECA-1.2, "LOCA Outside Containment," when a LOCA outside containment cannot be isolated.

ECA-1.1 instructs the Control Room Operators to verify that the ECCS pumps are not affected by sump blockage. If the ECCS pumps are indicating blockage, the operators are to enter procedure ECA-1.3, "Sump Blockage Mitigation."

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 ECCS and CS system, or result in significant quantities of debris being transported to the reactor vessel that would inhibit the necessary cooling of the fuel, th~y 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.

Contingency Option 2a: Deterministic Resolution Path Ameren Missouri will pursue Option 2a as a contingency plan, if the results of the risk-informed approach do not yield satisfactory results. Callaway Plant has evaluated the design and procedural capabilities that exist to identify and mitigate sump strainer and in-vessel blockage; as applicable the Callaway Plant sump strainer head loss and fiber load analysis will be revised using currently accepted methodologies.

Option 3: Different Regulatory Treatment for Suction Strainer and In-Vessel Effects (Deterministic for Strainer Head Loss /Risk-Based for In-Vessel Effects Resolution Path)

Ameren Missouri will maintain Option 3 as a separate contingency for the Callaway Plant, dependent on two things ( 1) the Pressurized Reactor Westinghouse Owners Group (PRWOG) evaluation and testing returning a new value for fiber loading in the core that Callaway Plant cannot meet and (2) if the results of the risk-informed approach do not yield satisfactory results. Callaway Plant will complete the deterministic resolution strategies to meet the resolution expectations for all aspects of GSI-191 as in Option 2a, except for in-vessel downstream effects, as identified in SECY-12-0093. For in-vessel downstream effects, Callaway Plant intends to follow a risk-informed or graded resolution path.

Conclusion Ameren Missouri expects that the GSI-191 resolution path for the Callaway Plant 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.

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