PNP 2013-041, Supplemental Information to Generic Safety Issue-191 Closure Option

Supplemental Information to Generic Safety Issue-191 Closure Option

ML13136A006
Person / Time
Site:	Palisades
Issue date:	05/15/2013
From:	Vitale A Entergy Nuclear Operations
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
PNP 2013-041, GL-04-002
Download: ML13136A006 (13)

Text

~ Entergy Entergy Nuclear Operations, Inc.

Palisades Nuclear Plant 27780 Blue Star Memorial Highway Covert, MI 49043-9530 Tel 269 764 2000 Anthony J. Vitale Site Vice President PNP 2013-041 May 15, 2013 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001

SUBJECT:

Generic Safety Issue-191 Closure Option Palisades Nuclear Plant Docket 50-255 License No. DPR-20

References:

1. Entergy Nuclear Operations, Inc. (ENO) letter, "Supplemental Response to NRC Generic Letter 2004-02, "Potential Impact of Debris Blockage on Emergency Recirculation During Design Basis Accidents at Pressurized-Water Reactors," dated February 27, 2008 (ADAMS Accession No. ML080630253)

2. ENO letter, "Request for Extension of Completion Date for Corrective Actions Required by Generic Letter 2004-02, "Potential Impact of Debris Blockage on Emergency Recirculation During Design Basis Accidents at Pressurized-Water Reactors," dated June 17, 2008 (ML081690612)

3. NRC letter, "Palisades Nuclear Plant - Issuance of Request for Additional Information Regarding Supplemental Responses to GL 2004-02 (TAC No. MC4701)," dated December 24,2008 (ML083450689)

4. ENO letter, "Response to Request for Additional Information Regarding Supplemental Responses to NRC Generic Letter 2004-02 (TAC No. MC4701)," dated March 20, 2009 (ML090790844 )

5. NRC letter, "Palisades Plant - Report on Results of Staff Audit of Chemical Effects Related Actions to Address Generic Letter 2004-02 (TAC No. MC4701)," dated May 13, 2009 (ML091070664)

6. ENO letter, "Follow-up Supplemental Response to NRC Generic Letter 2004-02," dated June 30, 2009 (ML091820275)

PNP 2013-041 Page 2

7. NRC letter, "Palisades Nuclear Plant - Request for Additional Information Regarding Actions to Address Generic Letter 2004-02 (TAC No. MC4701)," dated March 8, 2010 (ML100610654)

8. NRC letter, "Summary of May 12 and 13,2010, Meeting with Entergy Nuclear Operations, Inc., Regarding Response to Request for Additional Information for Generic Letter 2004-02 for Palisades Nuclear Plant (TAC No. MC4701 )," dated June 11, 2010 (ML101590527)

Dear Sir or Madam:

As documented in References 1, 4, 6, and 8, Entergy Nuclear Operations, Inc. (END) provided supplemental information to the Nuclear Regulatory Commission (NRC) concerning Generic Letter (GL) 2004-02 for Palisades Nuclear Plant (PNP).

On July 9, 2012, the NRC issued SECY 12-0093, which provided recommendations for closure options for Generic Safety Issue 191. END has selected the Risk-Informed version of Option 2. To support use of this path and continued operation for the period required to complete the necessary analysis and testing, END has evaluated the design and procedural capabilities that exist to identify and mitigate in-vessel blockage. A description of these detection and mitigative measures are provided in Attachment 1.

Additionally, a summary of the existing margins and conservatisms that exist for PNP are also included in Attachment 1.

Summary of Commitments This letter identifies six (6) new commitments (refer to Attachment 2) and completes the following commitment:

"END will report how it has addressed the in-vessel downstream effects issue within 90 days following the issuance of the NRC Safety Evaluation for WCAP-16793."

I declare under penalty of perjury that the foregoing is true and correct. Executed on May 15,2013.

Sincerely,

PNP 2013-041 Page 3 Attachments: 1. Generic Safety Issue 191 Closure Option

2. List of Regulatory Commitments cc: Administrator, Re.9ion III, USNRC Project Manager, Palisades, USNRC Resident Inspector, Palisades, USNRC

ATTACHMENT 1 GENERIC SAFETY ISSUE 191 CLOSURE OPTION 7 pages follow

Generic Safety Issue 191 Closure Option Introduction On July 9,2012, the NRC issued SECY-12-0093, "Closure Options for Generic Safety Issue - 191, Assessment of Debris Accumulation on Pressurized-Water Reactor Sump Performance." This SECY presented three options to the NRC, all of which are considered to be viable paths for resolving Generic Safety Issue (GSI) 191 (Reference 1). These options are: Option 1-Deterministic, Option 2- (Deterministic or Risk-informed), and Option 3-Deterministic/Risk-informed.

Entergy Nuclear Operations, Inc. (ENO) selected the Risk-Informed version of Option 2 for Palisades Nuclear Plant (PNP), because it has determined that performing a risk-informed evaluation of the potential for recirculation sump(s) strainer blockage and in-vessel blockage (South Texas Project [STP] approach) will resolve GSI-191, as identified in SECY-12-0093, for PNP.

To support use of this path, and continued operation for the period required to complete the necessary analysis and testing, PNP evaluated the design and procedural capabilities that exist to identify and mitigate sump strainer and in-vessel blockage. A description of these detection and mitigative measures are provided later in this document. Additionally, a summary of the existing margins and conservatisms that exist for PNP are also included in this document.

Characterization of In-Vessel Effects.

ENO intends to establish plant-specific in-vessel debris limits for the type of plant design that exists at PNP.

Licensing Basis Commitments In References 3 and 7, ENO committed to report to the NRC how it has addressed the in-vessel downstream effects issue within 90 days following the issuance of the NRC Safety Evaluation (SE) for WCAP-16793. As a result of the remaining open industry questions associated with closure of GSI-191 and to address GL 2004-02 for PNP, and the information contained within this document, the previously established commitment is considered to be closed based on the communication of the intended direction to be taken as described in this document.

Resolution Schedule ENO plans to achieve closure of GSI-191 and address Generic Letter (GL) 2004-02 for PNP with the following schedule:

• Meet with the NRC, as soon as practical after May 16,2013, to discuss this proposed resolution path.

• Complete measurements for insulation replacement by the end of the first refueling outage following January 1, 2013. That outage is scheduled to occur in October and November of 2013.

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• Submit a schedule for completion of the risk-informed resolution path activities by December 31, 2013, that provides for submittal of a licensing action following issuance of a SE for the STP license amendment request (LAR). The specific submittal schedule will be coordinated with the NRC.

• Complete any necessary insulation replacements or remediation, or other identified plant changes during the refueling outage that follows issuance of a SE for the risk-informed resolution LAR for PNP.

• Submit a final updated supplemental response to support closure of GL 2004-02 for PNP within six months of receipt of the SE.

o If it is determined during the risk-informed process that this option is not viable, complete a deterministic resolution path that is acceptable to the NRC within two refueling outages after the issuance of the SE for the LAR for STP.

o Update the current licensing basis following receipt of the SE that approves the risk-informed resolution approach and following the completion of any identified removal or modification of insulation debris sources in containment per plant modification procedures and processes.

Summary of Actions Completed For GL 2004-02 In response to GL 2004-02, ENO has completed the following actions:

• Replaced the existing sump strainer that had simple geometry and a surface area of 80 tf and Number 6 mesh (nominal 0.131 inch openings) with complex geometry strainers having a filtering surface area of 3524 ft2 and nominal 0.095 inch circular openings. The strainers modules are arranged in four different "banks" of modules that are physically separated on the 590 foot elevation of containment. They are jointly piped into two different containment sump downcomer pipes.

o Installed debris screens on the remaining open containment sump pathways, which include the four remaining downcomer pipes, the seven floor drains, and the two sump vents.

• Replaced the high pressure safety injection (HPSI) pump mechanical seals and cyclone separators with components that are not susceptible to premature failure due to fibrous debris, assuring that the HPSI pumps are capable of performing their safety-related design function during the required mission time of 30 days under post-loss of coolant accident (LOCA) conditions.

• Replaced the containment spray header valves with valves that can be set to a fixed throttled position during recirculation to conserve net positive suction head (NPSH).

• Changed the buffering agent from trisodium phosphate (TSP) to sodium tetra borate (NaTB) to decrease the magnitude of chemical precipitants.

• Changed the containment base slab configuration to eliminate two choke points that had the potential to hold up post-LOCA sump volume.

• Completed detailed containment walkdowns to identify and quantify the types and locations of debris sources. A separate walkdown was completed to take representative samples for latent debris quantities.

• Completed debris generation and debris transport analyses.

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• Completed ex-vessel downstream effects analysis. In-vessel effects analysis is still pending.

• Completed NPSH analysis for loss of coolant accidents.

• Implemented programmatic and procedural controls to maintain acceptable configuration. This includes controls for foreign material exclusion, aluminum control, containment coatings, labels, insulation, and dust and latent debris as well as design controls for engineering activities. PNP procedures containing these controls are:

o Administrative Procedure (AP) 1.10, "Plant System, Structure and Component Labeling" o AP 1.01, "Materiel Condition Standards and Housekeeping Responsibilities" o Specification M-136, "Furnishing and Installing Conventional Type Insulation" o Procedure EN-DC-115, "Engineering Change Process" o Procedure EN-DC-141, "Design Inputs" o Procedure EN-MA-118, "Foreign Material Exclusion" o Procedure RT-92 , "Inspection of Containment Sump Envelope" o Procedure MSM-M-71, "Containment Cleanliness Implementation Plan and Containment Closeout" o Procedure SEP-COAT-PLP-001, "Safety-Related Coatings Program Section" o Procedure MSM-M-42, "Application of Qualified Service Level I Coatings (Paint)"

o Procedure RM-124, "Sodium Tetraborate Basket Weights" 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 PNP.

Strainer Head Loss Analyses

• The debris transport analysis conservatively assumes 100% transport of fine particulate and fiber, coatings and latent debris.

• Strainer head loss testing utilized the minimum water level postulated for a large break LOCA.

• All unqualified coatings are assumed to fail and therefore are available to transport to the sump strainers.

• The debris transport analysis used incipient tumbling velocities corresponding to the lowest applicable values cited in the documents referenced in NEI 04-07, "Pressurized Water Reactor Sump Performance Evaluation Methodology," Table 4-2, for each type of debris.

• Strainer testing used bounding debris values as inputs for fiber and particulate by selecting values from two different break locations.

• The successful 2008 strainer test added chemical precipitate well beyond the design basis amount.

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• The strainer testing used aluminum oxy-hydroxide (AIOOH) as the chemical precipitant surrogate. AIOOH is considered conservative as a surrogate for the various aluminum precipitants that may form.

• A latent debris walkdown determined that the quantity in containment is approximately 156 pounds but the figure was increased to 200 pounds for debris generation and transport analyses.

• Containment overpressure is not credited in NPSH analysis. Any amount of pressure greater than that assumed in the NPSH analysis would provide additional margin for emergency core cooling system (ECCS) operability.

• The test protocol used for strainer head loss testing was specifically intended to attain a "thin bed" layer of debris that compacts tightly and produces the maximum head loss. The thin bed effect is achieved by assuming that debris and chemical products arrive at the strainer in a specific order. It is highly unlikely that debris that transports to the sump strainers would arrive in such an order. In addition, the protocol assumes that chemical precipitants form at the onset of the design basis LOCA (Le., large break LOCA). Chemical precipitants do not readily form in solution at temperatures above 130°F. The containment sump water temperature at the onset of a large break LOCA will be greater than 200°F.

In-Vessel Analyses

• The maximum flow rate through the containment sump (7.41 gpm per fuel assembly) is much less than half of the flow rate used (44.7 gpm per fuel assembly) to determine the bounding in-vessel fiber limit of 15 grams per fuel assembly. Testing showed that the lower flow rate results in a lower head loss across the fuel.

• The calculation that determined wear rates for downstream components assumed a minimum water inventory and maximum debris load to evaluate the effects of a bounding debris concentration.

• Sensitivity tests determined that the limiting in-vessel particulate to fiber (p:f) ratio for a hot leg break was a ratio of 1: 1. Since there is no way to know with any certainty what the timing and distribution of debris will look like, it is highly unlikely that the ratio would be 1: 1.

• The core design for PNP is unique in that it has cruciform control rod blades that are inserted between fuel assemblies. There is open flow area between the tips of the adjacent wings of the crucifixes. This open flow area extends the entire length of the fuel, including past the bottom nozzles that rest on the core support plate. There is an additional flow path in the narrow slot between the surfaces of the control rod and the surfaces of the fuel assembly. This configuration will tend to decrease the fouling rate of the fuel bundles since the debris will tend to follow the higher flow rate paths described.

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.

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Strainer Blockage o Two passive strainer assemblies with 0.095 inch openings were installed on the base slab (590 foot elevation) of the containment. The strainer assemblies connect to the containment sump via two containment sump down comer pipes.

The two strainer assemblies are physically separated on opposite sides of the containment. Due to the different path lengths and flow velocities determined by multiple computational fluid dynamics analyses, it is highly unlikely that a uniform debris bed would form on all strainers at the same time. Since the "thin bed" condition is limiting for strainer head loss, the extra thickness on one or more strainer assemblies will result in lower head loss.

o In addition to the two downcomers that are outfitted with strainer assemblies, there are four other containment sump downcomers and seven floor drain communication paths with screened openings in various locations around the containment base slab. These additional suction flow paths are not credited in the strainer head loss analyses.

o Operator actions for monitoring and detecting sump blockage were implemented within the Emergency Operating Procedures (EOPs) as described in the response to Bulletin 2003-01 (Reference 8).

o Steps have been added to EOPs to refill the safety injection refueling water (SIRW) tank. Actions were also added to the EOPs to secure unnecessary containment spray pumps in the period before recirculation alignment to conserve inventory in the SIRW tank and to reduce wash down of debris in the event of a small break loss of coolant accident. The pumps would be restarted immediately prior to recirculation in order to ensure HPSI subcooling after recirculation.

o The administrative limit for the minimum inventory in the SIRW tank in plant operating modes 1, 2 and 3 was increased from the Technical Specification minimum of 85% to a limit of 92%. The additional inventory delays the onset of recirculation and also provides 0.44 feet of margin for sump water level not currently credited in minimum NPSH analyses.

Fuel Blockage o Symptoms of core inlet blockage can be detected by existing core exit thermocouples (CETs) and the reactor vessel level monitoring system (RVLMS). This monitoring is initiated in the EOPs early in the event sequence.

An additional method of detecting the onset of core blockage would be the indication of increasing radiation levels in the containment building or auxiliary building.

o Upon identification of an inadequate primary coolant system (PCS) inventory or core heat removal condition, the EOPs direct the operators to take actions to restore cooling flow to the PCS including:

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

o Fill the PCS from alternate paths including using injection from the charging pumps.

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Conclusion ENO expects that the GSI-191 resolution path for PNP 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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References

1) NRC SECY-12-0093, "Closure Options for Generic Safety Issue -191, Assessment of Debris Accumulation on Pressurized-Water Reactor Sump Performance," dated July 9,2012 (ADAMS Accession Number ML121320270).

2) NRC 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 (ADAMS Accession Number ML12349A378).

3) ENO letter dated June 30,2009, "Follow-Up Supplemental Responses to NRC Generic Letter 2004-02" (ADAMS Accession Number ML091820275).

4) WCAP-16793-NP, "Evaluation of Long-Term Cooling Considering Particulate, Fibrous and Chemical Debris in the Recirculating Fluid," Revision 2, dated October 12, 2011 (ADAMS Accession Number ML11292A021 ).

5) PWROG Letter OG-12-287, "Submittal of Supplement to WCAP-16793-NP, Revision 2 (PA-SEE-0312, Revision 4)," dated July 20,2012 (ADAMS Accession Number ML12207A115).

6) Nuclear Management Company letter dated August 5, 2003, "Nuclear Regulatory Commission Bulletin 2003-01: Potential Impact of Debris Blockage on Emergency Sump Recirculation at Pressurized-Water Reactors Day Response" (ADAMS Accession Number ML032250084).

7) ENO letter dated March 20, 2009, "Response to Request for Additional Information Regarding Supplemental Responses to NRC Generic Letter 2004-02 (TAC No.

MC4701)" (ADAMS Accession Number ML090790844).

8) Nuclear Management Company letter dated May 17, 2004, "Supplement to 60-Day Response to Bulletin 2003-01, 'Potential Impact of Debris Blockage on Emergency Sump Recirculation at Pressurized-Water Reactors'" (ADAMS Accession Number ML041410026) 7

ATIACHMENT2 LIST OF REGULATORY COMMITMENTS 1 page follows

List of Regulatory Commitments The following table identifies those actions committed to by Entergy Nuclear Operations, Inc. (END) in this document. Any other statements in this submittal are provided for information purposes and are not considered to be regulatory commitments.

TYPE SCHEDULED (Check One)

COMPLETION COMMITMENT ONE-1-, ~. CONTINUING I -- DATE TIME COMPLIANCE (If Required)

ACTION END will meet with the NRC, as soon as September 1, 2013 practical after May 16, 2013, to discuss ./

this J>roposed resolution path.

END will complete measurements for By the end of the insulation replacement ./ first refueling outage following January 1, 2013.

END will submit a schedule for December 31, 2013 completion of the risk-informed ./

resolution path activities that provides for submittal of a licenSing action following issuance of a safety evaluation (SE) for the South Texas Project (STP) license amendment re-.9uest tLAR).

END will complete any necessary During the refueling insulation replacements or remediation, ./ outage that follows or other identified plant changes. issuance of a SE for the risk-informed resolution LAR for Palisades Nuclear Plant (PNP).

END will submit a final updated Within six months of supplemental response to support ./ receipt of the SE for closure of GL 2004-02 for PNP. the risk-informed resolution LAR for PNP.

If it is determined during the Within two refueling risk-informed process that this option is ./ outages after the not viable, END will complete a issuance of the SE deterministic resolution path that is for the STP LAR.

acceptable to the NRC.