ML20198J182
| ML20198J182 | |
| Person / Time | |
|---|---|
| Site: | Limerick  |
| Issue date: | 10/06/1997 |
| From: | Hunger G PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML20198J186 | List: |
| References | |
| IEB-96-003, IEB-96-3, NUDOCS 9710150010 | |
| Download: ML20198J182 (18) | |
Text
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10 CFR 50.90 10 CFR 50.59(c)
PECO NUCLEAR nm%c-Nuclear Group Headquarters A Uvr or P(CO f wc, 965 Chestertwook Boulevard Wayne. PA 19o87 5691 I
October 6,1997 Docket Nos. 50-352 50 353 License Nos. NPF.39 i
NPF 85 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington,DC 20555
Subject:
Limerick Gener6 ting Station, Units 1 and 2 Request for License Amendments Associated With ECCS Pump Suction Stralner Plant Modification Gentlemen:
This letter is tselng submitted in accordance with the requirements of 10 CFR 50.90 and 10 CFR 50.59 requesting license amendments to Facility Operating License Nos. NPF 39 and NPF 85 for Limerick Generating Station LGS), Units 1 and 2, respectively. PECO Energy is submitting this request to ootain NRC appro(val for implementation of a plant modification to support installati i
replacement suction strainers for the Emergency Core Cooling System (ECCS) pumps at LGS, i
Units 1 and 2. This plant modification is necessary in order to natisfy the recommendations i
stipulated in Bulletin 96-03," Potential Plugging of Emergency Core Cooling Suction Strainers by Debris in Boiling Water Reactors." Prior NRC approval for this plant modification is required.
l since the 10 CFR 50.59 Review prepared for this modification concluded that the proposed modification does constitute an Unreviewed Safety Question (USQ).10 CFR 50.59(c) requires i
that, for any changes to the facility involving a USQ, the licensee shall submit an application for amendment to its license pursuant to 10 CFR 50.90. The USQ that was identified pertains specifically to the design assumptions used for determining the amount of debris that would be expected to be generated under Loss of Coolant Accident (LOCA) conditions and the amount of material that would be transpc'ted to the Suppression Pool.
y Accordingly, the Attachment 1 to this letter contains the information supporting a no significant
/
hazards consideration in accordance with the requirements of 10 CFR 50.92. Attachments 2 5 to I
this letter contain additional documentation in support of this submittal This information is being submitted under affirmation, and the associated affidavit is enclosed.
/
. and Attachment 4 contain information of a proprietary nature to AGB. ABB requests that the information contained in Attachment 3 and Attachment 4 be withheld from public
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disclosure in accordance with 10 CFR 2.790(a)(4). As required by 10 CFR 2.790(b)(1), an
/ f affidavit supporting this request to withhold the information from public disclosure is provided in.
We are requesting that the NRC review and approve our request by March 20,1998, in order to support the installation of the replacement strainers for LGS, Unit 1, during its next refueling outage whleh is scheduled for April 1998.
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'Page 2-If you have any questions or require additional information, please do not hesitate to contact us,
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Very truly yours, haLpp.
G. A. Hunger, Jr.
Director. Licensing Attachments Fnclosure ec:
H. J. Miller, Administrator, Region I, USNRC (w/ Attachment 1, enclosure) i N. S, Perry, USNRC Senior Resident inspector, LGS (w/ Attachment 1, enclosure)
R. R. Jaratl, Director, PA Bureau of Radiological Protection (w/ Attachment 1, enclosure) 6 9
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ATTACHMENT 1 LIMERICK GENERATING STATION UNITS 1 AND 2 Docket Nos.. 50 352 50 353 License Nos. NPF 39 NPF-85 10 CFR 50.92 CVALUATION INFORMATION SUPPORTIN3 A NO SIGN!FICANT HAZARDS CONSIDERATION FOR ECCS PUMP SUCTION STRAINER REPLACEMENT MODIFICATION 4
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Page 1 of 11 10 CFR 50.92 EVALUATION INFORMATION SUPPORTING A NO SIGNIFICANT HAZARDS CONSIDERATION FOR ECCS PUMP SUCTION STRAINER REPLACEMENT MODIFICATION Stibjtc1 PECO Energy is submitting this license amendment request to obtain NRC approval for the implementation of a plant modificatio i to support installation of replacement suction strainers for Emergency Core Cooling System (ECCS) pumps at Limerick Generating Station (LGS), Units 1 and 2. This plant modification is necessary in order to satisfy the recommendations stipulated in Bulletin 96-03,
- Potentia' Plugging of Emer0ency Core Cooling Suction Strainers by Debris in Bolling Water Reactors? Prior NRC approval for this plant modification is required, since the 10CFR50.59 Review prepared for this modification concluded that the proposed modification does constitute an Unreviewed Safety Question (USQ). The USO that was identified pertains specifically to the design assumptions used for determining the amount of debris that would be expected to be generated under Loss of Coolant Accident (LOCA) conditions and the amount of material that wuld be transported to the Suppression Fool.
We are requesting that the NRC review and approve our request by March 20,1998, lit order to support the installation of the replacement strainers at LGS, Unit 1, during its next refueling outags which is scheduled for April 1998. This attachment contains the information supporting a no significant hazerds consideration in accordance with the requirements of 10 CFR 50.92.
Attachments 2 5 to this letter contain additional documentation in support of this submittal.
Specifically, these attachments contain the following information Attachmont 2 - General Plant Arrangement Drawing for the Replacement Strainer Locations Strainer Design Drewings (ABB Proprietary information) ion) Strainer Head Loss Correlation (ABS Proprietary informat ABB Affidavit Supporting Withholding From Public Disclosure On May 6,1996, the NRC issued Bulletin 96-03 requesting that Bolling Water Reactor (BWR) licensees implement appropriate procedural measures and plant modifications to minimtze the potential for clogging of Emergency Core Cooling System (ECCS) pump suction strainers by debris generated during a Loss-of-Coolant Accident (LOCA). The NRC indicated that these actions were necessary to ensure that the ECCS can perform its intended safety function and minimize the need for operator action to mitigate a LOCA. The NRC requested that the actions specified in Bulletin 96-03 be implemented by the end of the first refueling outage starting after January 1,1997.
In Bulletin 96-03 the NRC identified three (3) potential options for addressing the long term resolution of the ECCS pump suction strainer clogging in:lustry issue. In addition, the NRC also indicated that license.es may propose other attematives which provide an equivalent level of assurance that the ECCS will be able to perform its intended safety function following a LOCA.
The three (3) potential resolution options identified in the Bulletin are:
Ootion 1:
Installation of a Large Capacity Passive Strainer Design Ootion 2:
Installation of a Self-Cleaning Strainer Ootion 3:
Installation of a Backflush System PECO Energy evaluated various options and determined that the installation of large-capacity, passive, pump suction strainers (i.e., Option 1) is the most viable option for implementation at LGS, Units 1 and 2, in order to achieve a long term resolution for addressing the ECCS pump suction strainer clogging issue.
Page 2 of 11 i
This optio,1 utilizes a strainer design of sufficient capacity to ensure that debris loading effects following a LOCA, and as calculated in occordance 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.
- do not cause a loss of Net Positive Suction Head (NPSH) for the ECCS pumps. This design is completely passive and requires no operator intervention, nor does it require an interruption of ECCS flow for strainer cleaning or backflushing. Since this design reties solely on passive structures and components, no new Technical Specifications surveillance requirements for the strainers are required.
The new replacement strainers will be inetalled at Unit i during its next scheduled refueling outage, during a time period when the affected pumps are not required to be operable in accordance with Technical Specifications (TS). The Unit 2 work must be completed by December 31,1998, in accordance with an NRC letter dated January 6,1997 The work will be performed in j
accordance with approved procedures and will meet the requirements of a!! existing PECO
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Energy programs, e.g., Foreign Material Exclusion (FME) controls and control of heavy loads.
The new large capacity (replac? ment strainers will be installed on the Residual Heat strainers are not planned to be installed on the High Pressure Coolant injection (HPCI) and Reactor Core Isolation Cooling (RCIC) systems, since these systems are not required for initial reflooding following a large-break LOCA or for long-term cooling. In addition, the HPCI and RCIC pumps normally take suction from the Condensate Storage Tank (CST) rather than the Suppression Pool. The assumptions used in sizing the new replacement strainers for the LGS ECCS are discussed below, and are consistent with the guidance speclhed in RG 1.82, Revision l
2, and NUREG/CR-6224," Parametric Study of the Potential for BWR ECCS Strainer Blockage Due to LOCA Generated Debris."
Rafety Assessment i
Current Design Basis Tho suction strainers currently installed on the RHR systems at LGS, Units 1 and 2, are horizontally mounted, conical-shaped strainers with a maximum diametst of 24 inches, an overall length of 35 inches, and capable of filtering particles 1/16 of an inch and larger, Two (2) stra;ners are provided for each RHR pump. The strainers are designed for a clean pressare drop of 0.08 psi (0.18 feet) at a flow rate of 10,000 gpm. The current design basis pressure drop based on 50% plugging is 0.21 psi (0.48 feet) at a flow rate of 10,000 gpm. The minimum required NPSH for the RHR pumps at the design conditions is 5 feet.
The suction strainers currently instal'ed on the CS systems at LGS, Units 1 ano 2, are horizontally mounted, conical-shaped strainers with a maximum diameter of 16 inches, an overall length of 30% inches, and capable of filtering particles 1/16 of an inch and larger. Two (2) strainers are provided for each CS pump. The strainers are designed for a clean pressure drop of 0.05 psi (0.11 feet) at a flow rate of 3.950 gpm. The current design basis pressure drop based on 50%
plugging is 0.15 psi (0.35 feet) at a flow rate of 3,950 gpm. The minimum required NPSH for the CS pumps at the design conditions is 10 feet.
The original specified NPSH margins were 2 feet for both the RHR and CS pumps. This ma,ain was intended to offset manufacturing tolerances and differences in piping configuration. The available NPSH margin for the RHR pumps at a flow rate of 10,000 gpm, a Suppression Pool water temperature of 212' F, and a Suppression Pool air space pressure of 1 atmosphere is 14 feet (excluding strainer losses). The available NPSH margin for the CS pumps at a flow rate of 3,950 gpm, a Suppression Pool water temperature of 212' F, and a Suppression Pool airspace pressure of 1 atmosphere is 11.2 feet (excluding strainer losses). These margins represent the amount of head above that which is required.
The LGS ECCS is currently designed to meet the guidance specified in RG1.1,
- Net Positive Suction Head for Emcrgency Core Cooling and Containment Heat Removal System Pumps (Safety Guide 1),
Page 3 of 11 Since LGS has dedicated redundant passive suction strainers for each ECCS pumn, the most limiting accident and single failure scenario is the scenario which minimizes the number of ECCS pumps running and drawing suction from the suppressiol pool.
The desi n basis accident and most limiting single failure for LGS with respect to stralner sizing is 0
a recirculation suction line ureak coupled with a loss of offsite power and failure of Division i or 11 power which would render one (1) RHR pump and two (2) CS pumps hoperable (through the loss of the common CS Injection valve). This results in the following ECCS equipment operating initially and drawing suction from the Suppression Pool: three (3) RHR pumps in Low Pressure Coolant injection (LPCI) mode of oporation, and two (2) CS pumps (one (1) other CS pump will be I
operating at minimum flow, this flow is considered negligible). The HPCI and RCIC pumps are not included in this evaluation because they are not required for initial reflood following a large break l
LOCA or for long term cooldown, and their pump suctions are normally aligned to the Condensate Storage Tank instead of the Suppression Pool.
l The structural design loads of the suction stralners include dead weight, thermal, pressure, j
selsrr.lc and hydrodynamic loads. The limiting hydrodynamic loads are Safety Relief Valve (SRV) j l
bubble and seismic sloshing (Operating Basis Earthquake) for the upset load case, and SRV, LOCA chugging and seismic sloshing (Safe Shudown Earthquake) for the emergency and the i
faulted load cases.
l Modified Design Basis Summary 1
The proposed plant modification provides for replacement strainers on th M ' S pump suction I
lines (RHR and CS systems) of sufficient capacity to ensure that the EW win perform its intended safety funct on following a LOCA, considering debris loading effects.
The plant modification substantially changes the design basis for the ECCS suction strainers. The current ECCS suction strainer design for LGS assumes 50% plugging of strainers due to debric fouling. The new design includes substantial margir s in many of the design parameters. A discussion of the conservatism included in the sizing of the replacement strainers is as follows:
NPSH Margin:
Design margin is not typically required for NPSH. However,2 feet of NPSH margin is included in the design.
Zone of Destruction:
Insulation destruction testing conducted by the BWROG has shown that NUKON is destroyed at 10 psl. The zone of destruct on used to size the replacement strainer is based on a stagnation pressure of 4 psl.
Debris Generation.
The combined debris generation and transport fraction recommended by Trans.nort Fraction:
the BWROG in the " Utility Resolution Guidance for ECCS Suction Strainer Blockage" (URG) document for Mark ll containments is 14% for lines located above the lowest grating and 36% for lines located below the lowest grating. The combined debris generation and transport fraction used for sizing the replacement strainers for LGS is 100%.
Strainer Sizing:
The design basis for the design of the LGS strainers is the zone of destruction described above with 100% transport. This results in a Suppression Pool debris inventory of approximately 900 ft of fibrous 2
insulation, primarily NUKON. The fibrous debris used to size the actual strainers is 2000 ft'. Therefore the strainers are designed with operational margin of approximately 122% for the fibrous debris load.
Debris Settling:
No credit was taken for detris settling in the design of the new strainers, even though NUREG/CR 6224 recognizes that settling does occur.
1
Page 4 of 11 Corrosion Products:
The accumulation rate of corrosion products at LGS, based on observations from the last two (2) refueling outages is approximately 45 pounds per year. The accumulation used for sizing the replacement strainers is 1000 pounds.
Operational Debris:
Modeling the effects of the oporational debris for LGS by doubling the corrosion product inventory increases the calculated head loss for any given strainer by approximately 18% based on an estimate of the " bump up factors" as described in Volume 1 of the Technical Support Documentation to the Bolling Water Reactor Owners' Group (BWROG)" Utility Resolution Guidanco for ECCS Suction Strainer Blockage"(URG).
Hydrodynamic loads will also be determined using the currently licensed methodology except for the direct SRV hydrodynamic loads on the strainers, which will be oetermined using the methodology described in LGS UFSAR Section 3A.11. The methodology has been reviewed and approved by the NRC for calculation of SRV discharge loads on submerged structeres. It is the original methodology submitted with the Dynamic Forcing Function Report for the Mark 11 containment. The methodology was also approved and used in the Mark I and ill containments.
The 3RV bubble strength was determined from the boundary pressure and calibrated in the LGS lieplant tests, NPSH Marain Although no margin is required for NPSH, the proposed design basis for sizing the new replacement strainers rritains the original design basis objective, and limits the head loss of a fully fouled strainer to 2 feet less than the NPSH margin for each ECCS pump for those accident conditions cpecified above. The value of 2 feet was chosen to provide some additional operational margin. Therefore, the allowable head loss for en RHR pump suction strainer would be 12 feet and the allowable head loss for a CS pump suction strainer would be 9.2 feet (both at 212T) based on the following design debris considerations:
Insulation Type The LGS, Units 1 and 2, drywells contain substantial amounts of fibrous insulation (i.e., mostly NUKON material) primarily with protective stainless steel Jacketing. A combined bed of NUKON insulation and corrosion product / operational debris was used in sizing the new replacement strainers.
Zone of Destruction The zone of destruction (i.e., zone around a pipe break within which insulation is destroyed) to be uced at LGS for sizing the replacement strainers is conservatively estimated based on the volume associated with a fully expanding jet at a distance corresponding to a stagnation pressure of 4 psig. Since testing conducted by the BWROG showed that Jacketed or unjacketed NUKON was not destroyed at stagnation pressures of less than 10 psig, as discussed in the Utility Resolution Guideline (URG) document, this zone of destruction will bound the actual zone of destruction in the drywell. This volume was then converted to a spherical volume based on the methodology and data in the URG, Method 2. This spherical volume, was then placed within the drywell. Any portions of the sphere which intersected the drywell walls or vessel pedestal were eliminated from the zone. Also, any portions of the sphere with no line of sight to the assumed break location were eliminated from the zone of destruction. The remainder of the sphere was then used to define the zone in which insulation could be destroyed. All insulation contained within the zone was considered dertroyed for the purposes of sizing the riew strainers. Insulation other than NUKON, such as MIN-K and glass wool, has been shown to be destroyed at a stagnation pressure of 4 psig and greater, as discussed in the URG. Therefore, a zone of destruction based on a 4 psig stagnation pressure will capture the small quantity of other types of fibrous insulation material that may exist.
Page 5 of 11 Transport Fraction The percentage of destroyed insulation which could be expected to be transported to the Suppression Pool during the initial blowdown or subsequent washdown is defined as the transport fraction. Testing conducted by the BWROG, and as discussed in the URG, has shown that this fraction varies with the containment type and size of debris generated by the break. Defining the transport fraction in accordance with the URG for a Mark ll containment drywell, as LGS is, results in a fraction of 14% for insulation above the lowest grating and 36% for insulation below the lowest grating. However, for conseNatism, a transport fraction of 100% was assumed for the design of the LGS replacement suction strainers.
Pipe Break Location Even though there are no specific analyzed pipe break locations defined for LGS, for conservatism, the location of the center of the spherical volume for the zone of destruction was based on the area within the drywell containing the highest density of NUKON insulation material.
This volume provides a bounding volume of insulation for the head-loss calculation.
Debris Settling There was no credit taken for settling of insulation debris or corrosion products in th6 Suppression Pool.
Insulation Inventory As a result of the assumptions listed above, the maximum post accident fibrous insulation inventory, for any given break at LGS, is expected to be approximately 900 ft. Using this total, 8
the inventory for each strainer, when distributed in proportion to each individual strainer flow versus total ECCS flow, is defined as follows:
RHR: 121 ft8 8
CS:
86 ft The strainers were adequately sized and are capable of handling a total insulation load of 8
2000 ft.
Corrosion ProductInventory The corrosion product inventory value used for slzing the new replacement strainers was based on an accumulation rate of 100 pounds of corrosion roduct debris per year. This value is based on specific plant data obtained during the last two (2 refueling outages & LGS and Peach Bottom Atomic Power Station (PBAPS). The actual accumu ation rate was estimated at 45 pounds per year, based on measurements taken in the Suppression Pool. Since the corrosion product layer in the Suppression Pool was very thin, the accumulation rate for the design was increased to 100 pounds per year to account for possible measurement inaccuracles. The Suppression Pool corrosion product inventory assumed for the design was 1000 pounds, s
I Page 6 of 11 OperationalDeMs Only particulate debris was considered in the design of the replacement strainers. The design i
basis zone of destruction includes sufficient conservatism to bound any expected amount of fibrous operational debris. For particulate debris, no loading was explicitly calculat'sd. An additional 1000 pounds of corrosion products was assumed to bound operational debris in the basis for strainer sizing. This is considered to be a conservative bounding estimate for the following reasons:
1)
The LGS units have a steel containment that is coated with various zinc base coatings as described in the LGS UFSAR Table 6.1 5. Inorganic zine would be expected to fall in powder form, rather than delaminate 6,1 sheets or chips. Additionally, since the containment is steel, this limits the amount of concrete debris and duet which could be dislodged by a LOCA.
2)
The quantity of unqualified coating material (e.g., paint) in the drywell is small. The LGS UFSAR Table 6.1 6 lists the weight of unqualified coatings in the dryweel as 26 pounds for Nuclear Steam Supply System ((NSSS) equipment in the containment. Among non-NSSS com,poments, unqualified primers have been applied to pipes inside the drywell that has insulation covering the coating. As spec 9ed in UFSAR Section 6.1.2.3, the insulation will prevent any potential debris due to coating failure. However, during a LOCA event, some insulation will blow off and any coating material undemeath will no longer be contained. Since this quantity of primer / paint is relatively small, the total quantity will still be bounded by the 1000 pounds assumed.
3)
The BWROG URG recommends the following values for operational debris:
Inorganic Zinc: 47 unds Dust / Dirt i
pounds Rust Chips:
50 pounds Adding these quantities to the known unqualified paint total (i.e.,26 pounds), res.ts in an an.ount of debris (i.e.,273 pounds) which is well bounded by the 1000 pounds of additional corrosion products.
Adding the operational debris total to the Suppress %n Pool corroulon product inventory yields a total corrosion product inventory of 2000 pounds as the design basis for the stralners.
Other operational debris such as plastic bags and paper items are controlled as part of the Foreign Material Exclusion (FME ) Program. Procedural controls are in place in order to maintain primary containment cleanliness and to control introduction of forelon material. FME controls are instituted for work activities performed in the Drywell and Suppression Pool Closeout inspections of the Drywell and Suppression Pool are conducted, as appropriata, to ensure that any foreign material is removed upon completion of work activities. Plant personnel are instructed regarding the importance of plant cleanliness.
Replacement Strainers The sizing / design of the replacement strainers selected for use is based on vendor supplied head-loss correlations verified by prototypical test at the EPRI test facility. The strainers will be
' designed and structurally supported in order to withstand all expected forces including those resulting from misslies, debris accumulation, LOCA and SRV induced hydrodynamic loads, and design basis seismic events.
c
Page 7 of 11 lne current strainers were fabricated to American Society of Mechanical Engineers (ASME)
Section Vill, Pressure Vessels, but not stamped. The new replacement strainers will be fabricated in accordance with the applicable requirements of ASME Section ll!, Nuclear Power Plant Components but not stamped, since the strainers are not pressure retalning components.
Use of ASME Section lliis approprbte for this application. The strainers wili be fabricated of material that is not susceptible to corrusion (e.g.. stainless steel or equivalent) and will not be subject to degradation during long periods of inactivity and/or normal operations. The new replacement strainers will be added to the LGS, Ur'its 1 and 2, Inservice Inspection (ISI) Program.
The capability of filtering of the replaceme,it strainers will be maintained at particles 1/16 inch and larger.
SRVInduced Hydrodynamic Loads The direct hydrodynamic loads due to Safety Relief Valve (SRV) discharge events used for strainer design will be determined using the submerged structure methodology for SRV air bubble as described in LGS UFSAR Section 3A.11. This methodology uses the method of images to solve the potontial flow fields induced by osciliatory SRV bubbles and is the " generic
- Mark ll submerged structure load methodology accepted in NUREG-0487," MARK ll Containment Lead Plant Program Load Evaluation and Acceptance Criteria." This methodology was used for licensing LGS to demonstrate to the NRC that the bounding KWU T Ouencher submerged structure load specifiestion developed loads comparab'e to NRC accepted methods.
The bounding KWU T-Quencher submerged structure load specification was used in the design assessment of existing strainers. This methodology is Unight forward but conservative because it assumes that the bubble is adjacent to the strainers. Use of the " generic" methodology (i.e.,
method of images) allows more realistic determination of the submerged structure load on the new strainers because it considers the distance effect between the new strainers snd the SRV bubble sources. In calculating the design loads for the new replacement strainers, the bubble sourcs strength was calibrated to match the SRV boundary pressure load definition as described in LGS UFSAR Section 3B.4.1.
Planned Survelllances/ Inspections In order to assure that the accumulation of corrosion products does liot exceed the value assumed in the strainer design, PECO Energy will periocically inspect the new strainers and Suppression Pool.
If the design assumptions (i.e.,100 pounds of corrosion products per year)are exceeded PECO Energy will adjust the destudging interval accordingly. This periodic inspection interval is consistent with a previous commitment documented in our letter dated April 3,1997, responding to an NRC r0QJest for additional informstion concoming NRC Bulletin 9542, " Unexpected Clogging of a Residual Heat Removal (RHR) Pump Strainer While Operating in Suppression Poot Cooling Mode."
Proposed Technical Specifications Changes No new surveillance requirements will be imposed due to the level of conservatism included in the new replacem^nt strainer design. These components are strictly passive components and their operability will be adequately demonstrated through the existing Technical Specifications (TS) surveillance tests for the RHR and CS systems. This is consistent with the treatment of suction strainers in the current LGS TS.
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Page 8 of 11 Conclusions The new larger passive strainers are required to provide the required ECCS flows and minimum required pump NPSH for the RHR and CS pumps even when accounting for larger quantities of det-is postulated to be generated during a LOCA. The replacement ECCS suction strainers are designed to maintain the required NPSH for the RHR and CS pumps undir the most limiting design basis accident conditions. The design inputs for the sizing of the strainers bound the accident conditions and provide significant operational margin, information Sunoorting a Finding of No Significant Harards CanaldetAtlen We have concluded that the proposed plant modification for Limerick Generating Station (LGS),
Units 1 and 2, to replace Emergency Core Cooling System (ECCS) pump suction strainers for the Residual Heat Removal (RHR) and Core Spray (CS) systems, does not involve a Significant Hazards Consideration, in support of this determination, an evaluation of each of t; 0 three (3) standards set forth in 10 CFR 50.92 is provided below.
1.
The proposed change to the facility does not involve a significant increata in the orobability DLCDa$.RQuences of an accident orevious!v evaluated.
None of the components modified or replaced in this plant modification are accident initiators. They do not affect the nuclear fuel, the reactor pressure vessel, or any piping which forms the pressure boundary of the Nuclear Steam Supply System (NSSS).
Additionally, none of the components modified or replaced by this plant modification offect any of the barriers to fission product release previously evaluated. Compliance with current Technical Specifications will be maintained during installation.
This plant modification provides replacement strainers for the ECCS suction lines of sufficient capacity to perform their intended safety function following a Loss of Coolant Accident (LOCA), considering riebris loading effects. Since these stralners will be passive components, no changes will be required to procedures which provide controls, methods, or actions for activities performed at the plant or on plant systems, structures, or components.
All modifcation and maintenance activities will be done under approved plant procedures.
The new strainers are beirg added to increase the surface area to ensure operability of th6 ECCS pumps, and thereby, meintain long-term recirculation cooling capability during post LOCA conditions. These components are passive parts of the ECCS system and are installed only to mitigate the effects of an accident. This plant modification is needed in order to address recommendations imposed by NRC Bulletin (NRCB) 06-03,
" Potential Plugging of Emergency Core Cooling Suction Stralners by Debris in Bolling Water Reactors."
The heat capacity of the Supprestion Poolis not impacted by the replacement of the larger ECCS pump suction strainers. The volume of water displaced and the corresponding differenc 'n heat capacities betwt en the water displaced and the steel of the replacement strainer. o.ess thao.01% Therefore, the replacement strainers have no measurable effect on the capabilities of the Suppression Pool as a heat sink due to their increased size.
Attachmeht i Page 9 of 11 The larger strainers and their supports (if any) will be designed for the currently licensed seismic load methodology and load combinations. Hydrodynamic loads will also be determined using the currently licensed methodology except for the direct Safety Relief Valve (SRV) hydrodynamic loads on strainers, which will be determined using the methodology described in LGS Updated Final Safety Analysia Report (UFSAR) Section 3A.11. The methodology has been reviewed and approved by the NRC. It is the original methodology submitted with the Dynamic Forcing Function Report for the Mark ll containment. The methodology was also approved and used in the Mark I and lli containments. The SRV bubble strength was determined from the boundary pressure and calibrated in the LGS In-plant tests. Loads on other submerged structures are not changed due to the installation of larger ECCS suction strainers. The structure separation criterion will be reviewed and the suppression pool structure and supports will be analyzed to confirm that they are capable of accepting the potential load increase due to the larger strainers. This plant modifica4on will have no other detrimental impact on any other systems or portion of systems, structures or components.
This plant modification does not change, degrade or prevent the response of any existing plant system required to mitigate the radiological consequences of an accident previously evaluated. As such, the onsite and offsite radiological effects of any accident previously evaluated will not be impacted as a result of performing this plant modification. This modification will preserve the performance of the existing ECCS systems, given a change in the strainer design basis.
Tt'n original accident analysis previously evaluated did consider the introduction of insulation debris into tho Suppression Pool and its impact on ECCS oump operability. However, the head loss was assumed not to exceed 2 psi. Subsequent testing has shown this assumption to be non-conservative. Sizing of the replacement LGS pump suction strainers is based on ths guidance documented in the Bolling Water Reactor Owners' Group (BWROG)" Utility Resolution GuHance for ECCS Suction Strainer Blockage"(URG) document.
This plant modification does not adversely impact the barriers to fission product release previously evaluated. While the operability of the ECCS systems could affect the probability of fuel failure, the radiological conse ?Jonces of fuel failure are included in the current UFSAR analysis. The remaining ba..ers to fission product release, such as the primary and secondary containment. and Standby Gas Treatment System (SGTS) are unaffected by this plant modrfication.
Tnerefore, the proposed change to the facility does not involve an increase in the probability or consequences of an accident previously evaluated.
2.
The orooosed chance to the facility does not create the oossibility of a new or different kind of accident from any accident oreviousiv evaluated.
None of the components modified or replaced in this plant modification are accident initiators or affect any structures, systems or components which initiate accidents. This change only replaces the current Residual Heat Removal (RHR) and Core Spray (CS) suction strainers with stralners designed to maintain the required NPSH for the maximum post-LOCA debris loading. The replacement strainers are passive components which serve only to mitigate an accident. They meet all required hydrodynamic and seismic loading ard cannot initiate any s xident.
The replacement strainers do not actively control functions or responses of safety-related equipment. The installation of larger replacement strainers in response to a change in the design basis does not create any new accident scena-ios or any new failure modes.
Page 10 of 11 The original accident analysis previously evaluated did consider the introduction of insulation debris into the Suppression Pool and its effect on ECCS pump operability. However, the head loss was assumed not to exceed 2 psl. Subsequent testing has shown this assumption to bo non-conservative. Slzing of the replacement LGS suction strainers is based on the revised sizing guidance included in the BWROG URG. This guidance document is not generically approved by the NRC at this time. Therefore, the operability of the new strainers would be indeterminate prior to approval of the URG.
Therefore, the proposed change to the facility does not create the possibility of a new or different kind of accident from any accident previously evaluated.
3.
The oronosed change to the faellity does not involve a significant reduction in a marain of SRIn!L The margin of safety for the ECCS system is defined by the flow rates produced by the pumps, if the required NPSH is maintained, the ECCS pumps will deliver the rated flow.
The replacement suction strainers are designed to maintain the pressure drop across a fully fouled strainer to 2 feet less than the available NPSH margin for the RHR and Core Spray pumps under design basis LOCA conditions with the maximtm combined insulation and corrosion product debris loading.
The debris loading used for this design is based on a break of a Reector Recirculation line in the location in the drywell having the highest density of fibrous insulated piping. This location maximizes both the energy available to transport insulation debris and the possible number of targets. All of the insulation in the zone of destruction, described in the attached safety evaluation, is assumed destroyed and transported to the Suppression Pool, where it is available to be entrained on the replacement strainers combined with 2000 pounds of corrosion products / operational debris. No settling of debris is credhed in this design.
Since no design margin is required above the required NPSH to assure full pump flow, this design bounds all accident conditions, The design of the new strainers assures that adequate NPSH margin exists to maintain the current analyzed ECCS flow rates, even with increased debris loading. Therefore, this modification maintains the existing margin of safety as defined in the bases for the current Technical Specifications.
Therefore, this proposed change to the facility does not result in a significant reduction in any margin of safety.
Information Suonorting an Environmental Asse25 mini An Environmental Assessment is not required for the proposed changes to the facility since the proposed plant modification for LGS, Units 1 and 2, conforms to the criteria for ' actions eligible for categorical sclusion," as specified in 10 CFR 51.22(c)(5). The proposed plant modification will have no impact on the environment. The proposed plant modification does not involve a significant hazards consideration as discussed in the preceding section. The proposed plant modification does not involve a significant change in the types or significant increase in the amounts of any effluent that may be released offsite. In addition, the proposed plant modification does not involve a significant increase in Individual or cumulative occupational radiation exposure,
Page 11 of 11 r
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The Plant Operations Nview Committee and the Nuclear Review Board have reviewed the proposed changes to the facility as a result of this pioposed plant modification and concur that the changes de involve an Unreviewed Safety Question, and that the proposed changes will not ondanger the health and safety of the public.
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ENCLOSURE 1
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l COMMONWEALTH OF PENNSYLVANIA ss.
COUNTY OF CHESTER J. B. Cotton, being first duly swom, deposes and says:
That he is Vice President of PECO Energy Company, the Applicant herein; that he has read the foregoing information concoming the license amendment requests for Limerick Generating Station, Units 1 and 2, regarding replacement of Emergency Core CoolMg System pump suction strainers, and -
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l 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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Vice President Subscribed and swom to before me this 6 k day
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Notary PLblic NOTARIAL SEAL CAPIOL A. WALTO*, Notary Pubas
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Olty of PNiedelphia. h'ile. County My Commission E nowes May 2s. 2001
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OVERSIZE DOCUMENT PAGE(S) PULLED SEE APERTURE CARD FILES APERTURE CARD / PAPER COPY AVAILABLE THROUGH NRC FILE CENTER NUMBER OF OVERSIZE PAGES FILMED ON APERTURE CARD (S)$
ACCESSION NUMBERS OF OVERSl?E PAGES:
%ozIoo84 MI02.I008(;
DRP40
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