ML20029C728

Responds to NRC Bulletin 93-002,Suppl 1, Debris Plugging of Emergency Core Cooling Suction Strainers.

ML20029C728
Person / Time
Site:	Perry
Issue date:	04/19/1994
From:	Stratman R CENTERIOR ENERGY
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
IEB-93-002, IEB-93-2, PY-CEI-NRR-1791, NUDOCS 9404280232
Download: ML20029C728 (10)

Text

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t CENTERIOR

' ENERGY PERRY NUCLEAR POWER PLANT Mail Address: Robert A.Stratrnan P.O. BOX 97 VICE PRESIDENT . NUCLEAR 10 CENTER ROAD EW, ONO M 81 PERRY, OHIO 44081 (216) 259-3737 April 19, 1994 PY-CEI/NRR-1791 L U. S. Nuclear Regulatory Commission Document Control Desk Vashington, D. C. 20555 Perry Nuclear Pcver Plant Docket 50-440 Response to NRC Bulletin 93-02, Supplement 1: Debris Plugging of ECCS Suction Strainers Gentlemen On February 18, 1994, the Nuclear Regulatory Commission (NRC) issued Supplement 1 to Bulletin 93-02 concerning the potential for loss of net positive suction head (NPSH) for Emergency Core Cooling Systems (ECCS) due to debris plugging of ECCS suction strainers.

The specific interim actions and proposed implementation schedule are presented in Attachment 1 to this letter. The Perry Nuclear Power Plant (PNPP) has previously taken action to address many of these same issues in previous responses to Confirmatory Action Letter RIII-93-07 as described herein.

PNPP has taken a leadership role in the formulation of a Boiling Vater Reactor Owners' Group (BVROG) ECCS Suction Strainer Committee (a member of the engineering staff is Vice-Chairman of the committee) that is pursuing final resolution of this issue.

The enclosed response to supplement 1 to NRC Bulletin 93-02 satisfies the reporting requirements contained therein. If you have questions or require additional information, please contact Mr. Henry Hegrat - Regulatory Affairs at (216) 280-5606.

Very Truly Yours, i.f./"-A&/NNet'$7ni

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I, Robert A. Stratman, being duly sworn state that (1) I am Vice President, Nuclear - Perry of the centerior Service company, (2) I am duly authorized to execute and file this certification on behalf of The Cleveland Electric Illuminating Company and Toledo Edison Company, and as the duly authorized ,

agent for Duquesne Light Company, Ohio Edison Company, and Pennsylvania Power '

Company, and (3) the statements set forth herein are true and correct to the best of my knowledge, information and belief.

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Sworn to and subscribed before me, this / day.of JM[6 ,

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. PY-CEI/NRR-1791 L.

+ Attachment-1

- Page 1 of 8 RESPONSE TO NRC BULLETIN 93-02, SUPPLEMENT 1 On February 18, 1994, the NRC issued Supplement 1 to NRC Bulletin 93-02,

" Debris Plugging of Emergency Core Cooling Suction Strainers." The Perry Nuclear Power Plant has previously taken action regarding debris plugging of Emergency Core Cooling System suppression pool suction strainers in response to several incidents at Perry. This letter satisfies the first reporting requirement described within the NRC Bulletin Supplement. Actions requested within the NRC Bulletin Supplement are presented in boldface with the response provided immediately below.

1. Provide training and briefings to apprise operators and other appropriate emergency response personnel of the information contained herein and in the referenced information notices regarding the potential for suppression pool strainer clogging.

Training has been provided to Reactor Operators, Senior Reactor Operators, Shift Technical Advisors, and Operator Training Instructors about the various incidents described within the NRC Bulletin Supplement, regarding the potential for suppression pool strainer clogging, during the last operator training requalification cycle. This included recognition of changes in the various control Room parameters that might be indicative of suppression pool strainer clogging, including a demonstration of strainer clogging using the Control Room Simulator.

Training vill be provided in the form of " required reading" to selected emergency response personnel assigned to certain positions within the Emergency Response Organization (Technical Support Center and Emergency Operations Facility staff responsible for facility direction and operations oversight). This training is scheduled to be completed by May 18, 1994,

2. Assure that emergency. operating procedures (E0P' make the operator aware of possible indications of ECCS strainer clogg*ng and provide guidance on mitigation.

A combination of 1) the Emergency Core Cooling System (ECCS) and Reactor Core Isolation Cooling (RCIC) System Operating Instructions (SOIs), 2) the Plant Emergency Instructions (PEIs) [the PNPP emergency operating procedures], 3) training, and 4) a new event-based abnormal operating instruction, vill satisfy this requested action. A new event-based Off-Normal Instruction (ONI) is being developed to give the operator clear direction on possible indications of ECCS (or RCIC) suppression pool suction strainer clogging and provide guidance on mitigation. i Details of the indications available to the operator and discussions of mitigation methods are provided in the following paragraphs. An ONI is considered to be the proper instruction to address suppression pool suction strainer clogging because it is considered to be an event rather j than a symptom to be treated as is the case when utilizing the PEIs. The i

" Suppression Pool Suction Strainer Clogging" ONI will be effective, and i

PY-CEI/NRR-1791 L Attachment 1 Page 2 of 8 the operator required reading on this instruction vill be completed, by the end of the fourth refueling outage (RF04), currently scheduled for completion on June 8, 1994. Classroom instruction on this ONI will be conducted during the next scheduled operator requalification training classes, and vill be completed by July 30, 1994.

The operators. ability to diagnose this event is the key to mitigation.

Control Room indication is available which would indicate possible plugging of the ECCS (or RCIC) suppression pool suction strainers. This instrumentation includes reactor pressure vessel (RPV) vater level, pump flov, discharge pressure, pump amps and, most importantly, pump suction pressure. The operator would be directed to the " Suppression Pool Suction Strainer Clogging" ONI by the appropriate instrumentation Alarm Response Instruction when either a LOCA indication signal is present (Dryvell pressure greater than 1.68 psig) or when a ' low pump suction pressure annunciator alarm is received for the respective ECCS/RCIC System (s).

As described in more detail within the answer to Requested Action 3, Subpart e, the PNPP presently has low suction pressure annunciator alarus and indication in the Control Room for the high pressure injection systems (the High Pressure Core Spray (HPCS) and RCIC Systems) and is adding alarms for the Residual Heat Removal (RHR) A and B loops, .The Emergency Response and Information System (ERIS, the safety parameter display computer system at PNPP) vill, by the end of the fourth refueling outage, be capable of displaying the pump suction pressure for all the ECCS (and the RCIC System)'on the computer screens. The operator is trained to use these indications and will be cognizant of the ECCS/RCIC suppression pool strainer clogging issue. Upon receiving the above-indications, the operator would promptly take the appropriate actions including:

o Use those systems which are normally used to control RPV vater level during normal power operation. If offsite power is available, the Condensate and Feedvater Systems would be available. Note that .

these systems take suction from the condenser hotwell. The Control l Rod Drive System is available and can be supplied power from the emergency diesel generators if offsite power is unavailable.

These o Useinjectionsystemsthghavealternatesuctionsources.

and the RCIC Systems which can take systems include the HPCS suction from the condensate Storage Tank (CST).

- Note 1: PNPP is evaluating'providing direction in the PEI

flovcharts to direct the use of the CST as.the preferred.

- suction source for HPCS (this is already the case for RCIC). This enhancement is scheduled for incorporation in i

the PEI revision to be completed in August 1994, if'the evaluation results indicate that this enhancement can and t should be done, j

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PY-CEI/NRR-1791 L

. Attachmsnt 1

, Page 3 of 8 o To maximize the availability of the ECCS/RCIC Systems which take-suction from the suppression pool, the operator in accordance with the Off-Normal Instruction (where not in conflict with the PEIs) would:

a) Minimize ECCS/RCIC System flow not needed to restore and maintain PEI parameters within the specified limits _by throttling valves, b) PrepareotherECCS{ggICSystemsforoperation,butdonot initiate operation if the inservice system (s) can maintain level (to prevent entrainment of debris on the strainers when these systems would have been in standby) and, c) Alternate operation of ECCS/RCIC Systems if the inservice system performance degrades.

Note 2: PNPP is also evaluating providing guidance in the PEI flovcharts to direct the operators to prepare the ECCS Systems for operation but not to place the systems in the minimum flow or test modes if they are not immediately needed to maintain water level within PEI limits. This enhancement is scheduled for incorporation in the PEI i

revision to be completed in August 1994, if the evaluation results indicate that this enhancement can and should be done.

o Prepare for timely use of alternate injection systems including:

a) The RHR Loop B Flood (by the Emergency Service Water B Pump or the Diesel Fire Pump),

b) Injection via the Fuel Pool Cooling and Cleanup (FPCC) Header (Suppression Pool Cleanup (SPCU) Pump or Hotwell Pump),

c) Injection from the condensate Transfer System, d) Injection via the Standby Liquid Control System, and e) Injection via the " Fast Firevater System" tie-in to the HPCS Spray Sparger (being implemented during this refueling outage).

All of these alternate injection systems utilize a suction source other than the suppression pool, except for the SPCU Pump to FPCC Header combination.

3. Institute procedures and other measures to provide compensatory actions to prevent, delay, or mitigate a loss of available NPSH margin under LOCA' conditions. Such measures should be consistent with providing the design basis emergency system functions for core and containment cooling.

Actions to assure sufficient core and containment cooling may include ,

a) Reduction of flow (consistent with delivering the required ECCS flow) through the strainers to reduce head loss and extend the time for debris deposition.

PY-CEI/NRR-1791 L

. Attachment 1

. Page 4 of 8 <

f The PEIs dictate that the ECCS (and RCIC) pumps be manipulated to maintain RPV level within a directed band. If the RPV level can not be maintained above the top of active fuel (TAF) the NPSH limits are ignored and alternate injection systems are directed to be used.

The ONI vill instruct the operators to throttle the inservice ECCS/RCIC System (s) that are taking suction from the suppression l pool provided the requirements of the PEIs can be met. These 1 actions may reduce the rate of entrainment of debris and deposition  ;

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on the suppression pool suction strainers, thus prolonging the operability of the inservice ECCS/RCIC System (s). l b) Operator realignment of existing systems to allow backflushing of clogged strainers.

The " Suppression Pool Suction Strainer Clogging" ONI will direct the operator to backflush suppression pool suction strainer (s) in ,

accordance with the appropriate System Operating Instruction (s) }

(SOI). The RHR SOI was previously revised to include a section for backflushing the RHR A, B and C loop suppression pool suction strainers. This SOI utilizes the SPCU system pump to provide a flov l of water through the respective suppression pool suction strainer.in  ;

the reverse direction. The flow path can utilize either the CST or the suppression pool as the source of water to the HPCS suction line, through the SPCU pump into the FPCC header. The water is then directed into the RHR. suction piping via the RHR Fuel Pool Cooling Assist Suction Valve and through the suppression pool suction '

strainer (this flovpath was described in letter PY-CEI/NRR-0402L).

An additional method has been developed for backflushing the.RHR A and B loop suppression pool suction' strainers. This method vill be j added to the RHR S0I by the completion of refuel outage four (RF04). '

This method utilizes the condensate Transfer System pump (s) to  :

provide a flow of water through either of the RHR A or B suppression pool suction strainers in the reverse direction. The flow path utilizes the CST as the source of water through the RHR System Flush Valves. The vater is directed into the RHR suction piping (in the reverse direction to the normal flush path) via the RHR System Drain Lines to Radvaste.

PNPP is currently evaluating other methods for backflushing the ECCS (and RCIC) suppression pool suction strainers te further enhance our backflush capabilities.

c) Operator realignment of existing systems to allow injection to the core from vater sources other than the~ suppression pool.

1 As described in the answer to Requested Action 2, the PEIs developed from Revision 4 of the BVROG EPGs specify diverse and redundant l systems for controlling RPV vater level. Since the symptom-oriented -l PEIs address a full spectrum of initial plant conditions'and.  ;

postulated transients, the PEIs do not unconditionally prioritize (

use of one injection source over another. The PEIs are being evaluated to determine the validity of providing direction for using-

PY-CEI/NRR-1791 L

. Attachmsnt 1 Page 5 of 8 the CST as the preferred suction source for the HPCS. The proposed ONI will provide guidance on realignment of systems consistent with the requirements of the PEIs. The " Suppression Pool Suction Strainer Clogging" ONI will provide operators with a single reference which includes the available event specific accident mitigation options. Sources of RPV injection were described above in response to Requested Action 2.

d) Intermittent operation of the containment sprays when possible to reduce the transport of debris to the strainers.

During the Barseback incident, insulation was blown off the surrounding pipes / equipment / surfaces by the relief valve discharge in the Dryvell. Automatic containment spray operation occurred and provided a secondary mechanism for transporting (vashing) additional mineral vool insulation into the suppression pool. [ Note that this containment spray system would be more synonymous with the dryvell spray riode of RHR in some U.S. BVRs. ] The BVR/6 design does not >

have dryvell sprays. Because PNPP does not have dryvell sprays, this is not a secondary mechanism to vash additional debris from 1

breaks in the dryvell into the suppression pool in the event of a Loss of Coolant Accident.

Host BVR/6s, including PNPP, have a containment. spray mode of RHR to reduce containment pressure. However, due to the difference in Containment-designs between Barseback and PNPP, the effect on debris transport due to containment spray operation at PNPP in the event of a high energy line break would be different.

The high energy lines within the containment Vetvell (with a few exceptions) run through either the Steam Tunnel, are located in enclosed cubicles, or, are enclosed within guard pipes. Because almost all of the high energy lines in the Containment Vetvell are enclosed, containment spray operation vould not (except for breaks at a few locations) result in additiona'l insulation / debris washing into the suppression pool from the breaks (as occurred at Barseback) because the break area vould be inaccessible to the spray.

The containment sprays are designed to be automaticall/ initiated.

Hovever, containment spray operation vould normally be manually initiated in accordance with the guidance provided in the PEIs. The PEIs specify at which times and under what conditions'the containment sprays should be initiated and secured. No specific changes are currently contemplated to containment spray operation.

As described above, containment spray operation vould in most instances not result in the effects observed at Barseback.

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PY-CEI/NRR-1791 L Attachmsnt l' Page 6 of 8 e) Other plant-specific measures which assure availability of sufficient core and containment cooling to meet the design basis of the plant.

PNPP has previously taken extensive action regarding debris plugging of ECCS (and ROIC) suppression pool suction strainers in response to several incidents at PNPP. Detailed corrective actions have been developed in response to these incidents which help to-prevent and/or mitigate the loss of not positive suction head (NPSH) to the ECCS (or RCIC) pumps in the event of suppression pool strainer fouling. A summary is provided below. For detailed descriptions of the responses to the various issues, refer to the referenced letters.

1) Installation of Larger Suppression Pool Suction Strainers The former ECCS/RCIC suppression pool suction strainers were replaced with a new strainer design. This improved design is a truncated cone featuring larger diameter holes, increased total surface area, a larger flov area, and increased capacity for external pressure loading compared to the original design.- The guidance of Regulatory Guide 1.82, Revision 1 was utilized in establishing the replacement strainer design parameters. The improved design has been reviewed for the capability to withstand back-flush loads. For the purposes of evaluating NPSH margins, per Regulatory Guide 1.1 analysis, the 50% fouled ,

operating differential pressure of the strainers has been increased from 1 to 4 psid. A comparison of the strainer

• designs and a discussion of the design assumptions was presented in letters PY-CEI/NRR-0402L, 0404L and 0405L.

The replacement design strainer is less susceptible to fouling as it has a lover approach velocity and larger strainer holes and a larger surface and flov areas. The licensing basis NPSH has been verified as acceptable with the new 4 psid 6P/ fouling limit according to Regulatory Guide 1.1.

2) Realistic NPSHA Determining a realistic net positive suction head available (NPSHA).rather than utilizing the design NPSHA cased on Regulatory Guide 1.1 and the other licensing assumptions results in a very significant increase in the available NPSH margin.

> Utilizing the peak suppression pool post-accident water temperature of 185 F rather than the prescribed licensing value of 212 F (and the actual 50% fouled strainer 6P, rather than the 4 psid value assumed previously), results in an increase in available NPSH margin from 1.3 feet (currently given credit for in the licensing basis for the pump with the least margin) to 24.5 feet. Note that this amount of NPSHA improvement is.

available for all of the ECCS pumps. Realistic NPSH margins,.

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PY-CEI/NRR-1791 L' 4 . Attachmsnt 1

. Page'7 of 8 i for various BVR plants, vere presented previously in Attachment 1 to the "BVROG Interim Safety Assessment and Operator Guidance Response to NRC Bulletin 93-02, Supplement 1," submitted under letter BVROG-94034, dated March 24, 1994.

3) ECCS (and RCIC) Pump Suction Pressure Monitoring Capability As indicated in the response to Requested Action 2, PNPP vill have Control Room instrumentation with the capability to monitor the suction pressure for each of the ECCS (or RCIC) pumps at the completion of the current refueling outage as described below:

Low Suction Press. ERIS Point ECCS (or RCIC) System Alarm Annunciator Suction Ind.

High Pressure Core Spray Yes Yes Reactor Core Isolation Yes Yes Cooling Low Pressure Core Spray No Yes Residual Heat Removal "A" Yes Yes Residual Heat Removal "B" Yes Yes Residual Heat Removal "C" No Yes As noted above, ECCS (and the RCIC System) pump suction pressures vill be capable of being monitored from the ERIS computer screen displays. _PNPP is also adding lov suction pressure annunciator alarms for the two most important low pressure injection systems, RHR Loops A and B, during the current refueling outage. These loops of the RHR System are used for long-term core and containment cooling and for placing and maintaining the reactor in cold shutdown.

4) Backflush Capability As described previously in the response to Requested Action 3, Subpart b, the RHR A and B loops vill each have two proceduralized means to backflush the suppression pool suction strainers at the completion of this refueling outage. RHR Loop C has one method procedural 12ed to backflush the loop. No methods have been identified to date to backflush the Low Pressure Core Spray, the HPCS, or the RCIC Systems. However, both the HPCS and the RCIC Systems can take suction from an alternative source, the CST.

5) Housekeeping and Cleanliness Control Program The PNPP has developed procedures and instructions to ensure good Drywell and Containment housekeeping practices and i suppression pool cleanliness as described in our response to l

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PY-CEI/NRR-1791 L Attachment 1 Page 8 of 8 Confirmatory Action Letter RIII-93-07 (letters PY-CEI/NRR-0402L, 0404L and 040SL). These letters describe the housekeeping and inspection criteria for the Containment, Dryvell and the suppression pool both durirg shutdown / refueling operations and during power operation._ These letters also describe the material accountability and work control practices that have been strengthened to alleviate the introduction of foreign materials into the suppression pool.

6) Operational Monitoring and Surveillance Program PNPP has developed improved inspection standards and surveillance techniques to ensure that the enhanced housekeeping and cleanliness control program noted in Item S above is maintained. Details of these methods were described in our response to Confirmatory Action Letter RIII-93-07 (letters PY-CEI/NRR-0402L, 0404L and 0405L). Some of these improvements include monitoring and trending of the pump suction pressures during Technical Specification surveillance testing, visual inspection of the suction strainers during Technical Specification surveillance testing and visual inspection by the operators during the daily Plant Equipment Rounds, and revisions to the plant chemistry control program to provide indication of corrosion product build-up and/or the presence of' fibrous material in the suppression pool.

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