ML20129K169

Forwards Response to NRC Bulletin 96-003, Potential Plugging of ECC Suction Strainers by Debris in Bwrs

ML20129K169
Person / Time
Site:	Peach Bottom, Limerick
Issue date:	11/01/1996
From:	Hunger G PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
IEB-96-003, IEB-96-3, NUDOCS 9611080201
Download: ML20129K169 (9)

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Stati n support Diptrtmtnt NRCB No. 96-03 Z

10CFR50.54(f) v PECO NUCLEAR eeco eoee, cemneev 965 chestertwook Boulevard A Unit of PECO Energy Wayne, PA 19087-5691 i

November 1,1996 Docket Nos. 50-277 50-278 50-352 50-353 Ucense Nos. DPR-44 DPR-56 NPF-39 NPF-85 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555 Subject Peach Bottom Atomic Power Station, Units 2 and 3 Limerick Generating Station, Units 1 and 2 Response to NRC Bulletin 9643, " Potential Plugging of Emergency Core Cooling Suction Strainers by Debris in Bolling Water Reactors" 1

i Attached is PECO Energy Company's response to NRC Bulletin (NRCB) No. 96-03, " Potential I

l Plugging of Emergency Core Cooling Suction Strainers by Debris in Bouing Water Reactors," for Peach Bottom Atomic Power Station (PBAPS), Units 2 and 3, and Limerick Generating Station (LGS), Units 1 and 2, which was issued on May 6,1996.

This Bulletin requests that licensees implement appropriate procedural measures and plant modifications to minimize the potential for clogging of Emergency Core Cooling Systems (ECCS) suppression pool pump suction strainers by debris generated during a Loss-of-Coolant-Accident (LOCA). The NRC considers these actions necessary in order to ensure the capabuity of the ECCS to perform its intended safety function. The NRC identified three (3) potential resolution options in this Bulletin; however, licensees may propose other methods which provide an ary'&t level of assurance that the ECCS will respond and provide adequate reactor core cooling capability following a LOCA. The NRC requested that licensees implement the actions identified in this Bulletin by the end of the first refueling outage starting after January 1,1997. In addition, NRCB 96@l requires that all BWR licensees provide a written response within 180 days of the date of this Bulletin indicating whether the licensee intends to comply with the " Requested l

Actions" stipulated in the Bulletin. This response should include a description of the planned actions and mitigative strategies to be used, the schedule for implementation, and proposed i

Technical Specifications changes, if appropriate.

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November 1,1996 Page 2 The attachment to this letter provides PECO Energy's response to NRCB 96-03. The reporting requirements identified in the Bulletin are restated in the attachment followed by our response for PBAPS, Unks 2 and 3, and LGS, Units 1 and 2. This response is being submhted under affirmation in accordance wkh 10CFR50.54(f), and the required affidavit is enclosed.

If you have any questions or require addklonal information, please do not heskate to contact us.

Very truly yours,

$ f. A$ )=op G. A. Hunger, Jr.

Director - Licensing Attachment Enclosure l

cc:

H. J. Miller, Administrator, USNRC, Region I (w/ attachment & enclosure)

N. S. Perry, USNRC Senior Resident inspector, LGS (w/ attachment & enclosure)

W. L Schmidt, USNRC Senior Resident inspector, PBAPS (w/ attachment & enclosure) l t

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j COMMONWEALTH OF PENNSYLVANIA t

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COUNTY OF CHESTER D. B. Fetters, being first duly sworn, deposes and says:

That he is Vice President of PECO Energy Company; that he has read the foregoing response to NRC Bulletin 9643, " Potential Plugging of Emergency Core Cooling Suction Strainers by Debris in Boiling-l Water Reactors," for Peach Bottom Atomic Power Station, Units 2 and 3, and Umerick Generating Station, i

Units t end 2, and knows the contents thereof; and that the statements and matters set forth therein are true and correct to the best of his knowledge, information, and belief.

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y Vice President Subscribed and sworn to before me this [6 7 day pyy(,[f/L/1996.

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i ATTACHMENT Peach Bottom Atomic Power Station, Units 2 and 3 Limerick Generating Station, Units 1 and 2 Response to NRC Bulletin 96-03, " Potential Plugging of Emergency Core Cooling Suction Strainers by Debris in Boiling Water Reactors" l

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I Attachment NRC8 96-03 Response 4

Page 1 of 5 Peach Bottom Atomic Power Station, Units 2 and 3 Limerick Generating Station, Units 1 and 2 Response to NRC Bulletin 96 03 4

On May 6,1996, the NRC lasued NRCB No. 96-03, " Potential Plugging of Emergency Core Cooling Suction Strainers by Debris in Boiling Water Reactors," requesting that Boiling Water Reactor (BWR) licensees implement appropriate procedural measures and plant modifications to minimize the potential for clogging of Emergency Core Cooling System (ECCS) suppression pool pump suction strainers by debris generated during a Loss-of-Coolant-Accident (LOCA). The NRC indicated that these actions were j

necessary to ensure that the ECCS can perform ks intended safety function and minimize the need for operator action to mitigate a LOCA. The NRC requested that the actions specified in NRCB 96-03 be implemented by the end of the first refueling outage starting after January 1,1997.

In NRCB 96-03 the NRC identified three (3) potential options for addressing the long term resolution of the ECCS pump suction strainer clogging industry issue. In addition, the NRC also indicated that licensees may propose other attematives which provide an equivalent level of assurance that the ECCS wNI be able to perform its intended safety function following a LOCA. The three (3) potential resolution 1

options identified in the Bulletin are discussed briefly below.

Ootion 1: installation of a large Capacity Passive Strainer Design This option utilizes a strainer design of sufficient capacity to ensure that debris loading effects following a LOCA, and as calculated in accordance wkh the guidance specified in Regulatory Guide (RG) 1.82, Revision 2, " Water Sources for Long-Term Recirculation Cooling Following a Loss-of-Coolant-Accident," do not cause a loss of Net Positive Suction Head (NPSH) for the ECCS pumps.

This design is completely passive and requires no ope ator intervention, nor does k require an interruption of ECCS flow. Licensees choosing this option should establish new or modify existing programs, as necessary, to ensure that the potential for debris to be generated and transported to the ECCS pump suction strainers' surface following a LOCA does not at any time exceed the assumptions used in estimating the amounts ci debris for sizing of the strainers in accordance with RG 1.82, Revision 2.

Ootion 2: Installation of a Gelf-Cleaning Stralner This option introduces a strainer design that prevents clogging by providing continuous cleaning of the strainer surface by use of a blade or brush device. Uke Option 1 above, this design does not require any operator action or interrupt ECCS flow. However, this option does rely on an active component which is fully exposed to the LOCA effects in the suppression pool to keep the ECCS pump suction strainers' surface clean. As a n suit, appropricte measures should be taken to ensure operabilky of the strainer. Installation of this type of strainer should be combined with 1) implementation of reasonable measures to eliminate debris sources that could potentially damage or overload the strainer following a LOCA (this include 3 removal of all debris from the suppression pool every refueling outaga), and 2) implementation of surveillances to ensure adequate cleaning of the suppression pool and the operability of the strainers.

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Attachment NRCB 9603 Response i

Page 2 of 5 Option 3.

Irwanathn of a Backflush System This option employs a backflush system wh'ch is a reactive system that relies on operator action to remove accumulated debris from the surface of the ECCS pump suction strainers to prevent clogging in order to ensure that an operator can adequately respond to a suction strainer clogging event, installation of a backflush system should be combined with the following measures: 1) reasonable efforts to maximize the amount of time before clogging could occur; 2) instrumentation

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and alarms to indicate when strainer differential pressure (aP) increases; 3) operator training on recognition and mitigation of a strainer clogging event; and 4) implementation of survelilances to ensure operabuity of the strainer instrumentation and backflush system. In addition, a supporting analysis for the installation of a backflush system that is consistent with the guidance specified in RG 1.82, Revision 2, should be performed to demonstrate that operators have sufficient time to j

recognize the onset of strainer J 'gging and to take appropriate action.

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The NRC considers that Technical Specifications (TS) should be proposed to support surve8lances for l

components and systems installed in response to this Bulletin and should include, where appropriate, for l

the resolution option selected, surve81ance testing of active features (i.e., Options 2 and 3), and visual Inspections where they provide reasonable assurance that the component is operable.

In addition, NRCB 96-03 requires that all BWR licensees provide a written response within 180 days of the date of this Bulletin as stipulated in the " Required Response" section of NRCB 96-03 The Reporting Requirements specified in this Bulletin are restated below followed by PECO Energy's response for PBAPS, Units 2 and 3, and LGS, Units 1 and 2.

l Reportina Reauirement 1 Within 180 days of the date of this bulletin, a report indicating to what extent the licensee intends to comply with the requested actions, including a description of planned actions and mitigative strategies to be used, the schedule for implementation, and proposed TS, if appropriate; or, if the licensee does not intend to comply with these actions, a detaled description of the safety basis for the decision. The report must contain a detaued description of any proposed alternative course of action, the schedule for completing this altemative course of action, the safety basis for determining the acceptabuity of the planned attemative course of action, and proposed TS, if appropriate, that support the proposed attemative course of action and that are consistent with 10CFR50.36. The NRC considers the 180< lay response period appropriate, given the amount of engineering that j

licensees may wish to perform before they provide their formal response to the NRC.

Response

PECO Energy has evaluated the various options identified in NRCB 96-03 and determined that the installation of large-capacity, passive, pump suction strainers (i.e., Option 1 in NRCB 96-03) is the most viable option for implementation at Peach Bottom Atomic Power Station (PBAPS), Unit 2 and 3, and Limerick Generating Station (LGS), Units 1 and 2, in order to achieve a long term resolution for addressing the ECCS pump suction strainer clogging issue.

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Attachment NRCB 96-03 Response Page 3 of 5 PECO Energy wHl instau large<:apacity, passive, strainers on the Residual Heat Removal (RHR) and Core Spray (CS) system pump suction lines at PBAPS, Units 2 and 3, and LGS, Units 1 and 2. The assumptions used in sizing these new strainers for the PBAPS and LGS ECCS are described below, and are consistent with the guidance specified in Regulatory Guide (RG) 1.82, Revision 2, " Water Sources for Long-Term Recirculation Cooling Following a Loss-of-Coolant-Accident," and NUREG/CR4224, " Parametric Study of the Potential for BWR ECCS Strainer Blockage Due to LOCA Generated Debris" Zone of Destruction The zone of destruction to be used at PBAPS and LGS for sizing the strainers wiH be conservatively estimated, as a minimum, to be based on the volume associated with a fully expanding jet at a distance corresponding to a stagnation pressure of 4 psig. This volume wHl then be converted to a spherical volume based on the data contained in Volume ll, " Zone of influence as Defined by Computational Fluid Dynamics," of the Technical Support Documentation to the UtHity Resolution Guideline (URG). This spherical volume, which wWI be centered at the worst break location, wHI be used to define the zone of influence. All insulation l

material contained in this zone wHI be considered destroyed. The transportable fraction of the destroyed insulation wHl be conservatively defined to bound any possible accident scenarios and afford substantial design margin and conservatism.

l Ploe Break Location The location of the center of the spherical volume for the zone of influence to be used at PBAPS and LGS will be chosen so that the volume of debris generated wHl be the most conservative value. The location wHl be selected by determining the area within the drywell containing the highest density of NUKON insulation material. Since this volume WHI tie bounding, no specific pipe break analysis wHl be performed Irmdahn Tyne Both PBAPS and LGS drywells contain substantial amounts of NUKON (fiberglass) insulation, primarHy with protective stainless steel jacketing. Our preliminary calculations indicate that the

(,orresponding loss in Net Positive Suction Head (NPSH) associated with NUKON insulation material bounds the head 4oss for Reflective Metallic insulation (RMI) at both PBAPS and LGS.

in addition, Bouing Water Reactor Owners' Group (BWROG) testing has shown that a combined bed of RMI and NUKON insulation along with the deposition of corrosion product debris.dges agt increase the head-loss for the combined bed. Therefore, only a combined bed of NUKON insulation and corrosion product debris will be considered in sizing the new strainers at PBAPS and LGS.

Transoort Factor A transport factor of 100% will be used at PBAPS and LGS for sizing the strainers.

Debris Settling i

There will be 30 credit taken for debris settling in the torus / suppression pool at PBAPS and LGS.

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NRCB 96-03 Response Page 4 of 5 a

i Corroalon Product Inventory The corrosion product inventory value used for sizing the new strainers at PBAPS and LGS wHl be based on an accumulation rate of 100 pounds of corrosion product debris per year. This value is based on specific plant data obtained during the last two (2) refueling outages at PBAPS. Actual measurements estimated the accumulation rate at 45 pounds per year.

Therefore, using a debris generation rate of 100 pounds per year is considered conservative and provides adequate design margin. SimHar practices are being used at PBAPS and LGS to control torus / suppression pool water conductivity, and therefore, this value is considered acceptable for use at PBAPS and LGS. However, this value wHl be verified for LGS prior to completing the final strainer design The desludging interval will be chosen to coincide with other periodic inspections of the suppression chambers and to bound the accumulation of other operating debris which may be generated (e.g., paint chips, dust, etc.).

Ooerational Debris No loading for operational debris wul be explicitly calculated. PECO Energy considers that the insulation and corrosion product loading assumed for sizing the strainers is sufficiently conservative to bound all accident debris loading scenarios.

The new strainers wul have more than adequate surface area to ensure operability of the ECCS pumps, and thereby, maintain long-term recirculation cooling capability during post LOCA conditions. After installing the new strainers, it wHl not be necessary to routinely inspect and clean the suppression pools at PBAPS and LGS. Therefore, suppression p >ol inspections, and any cleaning that may be necessary, can be coordinated with other perioclic inspection activities (e.g.,

inservice Inspection (ISI) Program inspections and coat!ng inspection s).

The size and shape of the strainers wHi be such to avoid a loss of NPSH for ECCS pumps as a result of debris deposition on the strainers during the period t%c the ECCS is required to operate to ensure long-term cooling capabHity. The strainers currently being considered are a stacked disk configuration. However, PECO Energy will be reviewing other strainer designs as they become available. The sizing of the final strainer design selected for use wHI be based on the methodology contained in the BWROG Attemate Strainer Test Report. If the final strainer design is not sufficiently simHar to the strainers tested by the BWROG to allow the use of this test data, the final design wHl be tested at the EPRi test faculty urder conditions identical to the original test plan. The strainers will be designed and structurally supported in order to withstand the expected forces resulting from missues, debris accumulation, LOCA-induced hydrodynarnic loads, and design basis seismic events.

The design of the new strainers wul require a reanalysis of the hydrodynamic loads at LGS, and could include a reenalysis of the loads for PBAPS should the avaHable design margins be insufficient l

to support the installation of structural support components for the new strainer structures. This reanalysis could result in an unreviewed safety question that requires prior NRC approval before the strainers can be installed.

PECO Energy is not committing to fabrkating the new strainers in accordance with the applicable requirements of tne American Society of Mechanical Engineers (ASME) Codes, as requested in NRCB 96-03, since these strainers are not pressure retaining components. However, the strainers will be fabricated of material that is not sasceptible to corrosion and degradation during periods of j

inactMty and normal operations. In addition, since this design relies solely on passive structures and components, PECO Energy does not plan on implementing any new Technical Specifications i

surveillance requirements for the strairars as requested in this Bulletin. The new strainers wHl be I

included in the Inservice inspection (ISl Programs at PBAPS, Units 2 and 3, and LGS, Units 1 and 2.

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Attcchment NRCB 96-03 Response l

Page 5 of 5 PECO Energy is planning to instaN the new strainers on the low pressure ECCS (i.e., RHR and CS)

J pump suction piping during future refueling outages at PBAPS, Units 2 and 3, and LGS, Unit 1 and

2. We areagt currently planning to install new strainers on the High Pressure Coolant injection (HPCI) system pump suction piping at PBAPS and LGS, since the primary suction supply for the HPCI system pumps at PBAPS and LGS is the Condensate Storage Tank (CST), and not the torus / suppression pool. In addition, the HPCI system does not function to provide long-term cooling capabbity following a LOCA. The schedules for implementing these plant modifications are provided below ECCS Suction Strainer implementation Schedule PBAPS

.LQ.S Unit 2 2RO12 (September 1998)

Unit 1 - 1RO7 (AprH 1998)

Unit 3 - 3RO11 (September 1997)

Unit 2 - 2ROS (AprH 1999)

These schedules were developed based on the recommendations provided in NRCB 96-03, which requests that licensees implement the appropriate plant modifications by the end of the first refueling i

outage starting after January 1,1997. However, by letter dated September 6,1996, PECO Energy requested that the installation of the modification for LGS, Unit 2, be deferred unti the fifth refueling outage (2ROS). T"9re is not adequate time to complete the necessary engineering, procurement, and fabrication acdvkies to support installation of the modification during the fourth refueling outage (2RO4) which is scheduled to begin in January,1997. The justification and compensatory actions

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that wiH be taken to support this deferral were provided in our September 6,1996 letter. This l

request is currently pending NRC approval. If the NRC does not approve our request to defer the implementation of the modification work for LGS, Unit 2, untH 2ROS, as requested, it wul be i

necessary for PECO Energy to reevalute its options.

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I In the interim, PECO Energy wil continue to monkor ECCS pump differential pressure (dP) data (wkh the exception of the HPCI system) for any indication of pump performance degradation. We wul also continue to analyze the torus and suppression pool water samples that are routinely taken at PBAPS and LGS for evidence of visible fibrous material. These activities will continue untH the new strainers are installed at PBAPS and LGS. In addition, Foreign Material Exclusion (FME) controls wiu be implemented and monitored in accordance with PBAPS and LGS existing plant administrative procedural controls to ensure plant cleanliness, especially in the areas of the drywell and torus / suppression pool.

Ernortina Reauirement 2 Within 30 days of completion of all requested actions, submit a report confimiing completion and summarizing any actions taken.

Response

PECO Energy wul submit a report within 30 days after completing the installation of the ECCS pump i

suction strainer modifications at PBAPS, Units 2 and 3, which summarlzes the actions taken. A simaar report wil be submitted for LGS, Units 1 and 2, within 30 days after completing the modifications at LGS.

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