ML20029C753

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

ML20029C753
Person / Time
Site:	Duane Arnold
Issue date:	04/19/1994
From:	Franz J AFFILIATION NOT ASSIGNED
To:	Russell W NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM), Office of Nuclear Reactor Regulation
References
IEB-93-002, IEB-93-2, NG-94-1391, NUDOCS 9404290035
Download: ML20029C753 (5)

Text

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UTILITIES INC.

John F Franz. Jr.

Vice President. Nuclear April 19, 1994 NG-94-1391 Mr. William T. Russell, Director ,

Of fice of Nuclear Reactor Regulation - .

U. S. Nuclear Requlatory Commission Attn: Document. Control Desk Mail Station F1-137 Washington, DC 20555

Subject:

Duane Arnold Energy Center Docket No: 50-331 Op. License No: DPR-49 Response to NRC Bulletin 93-02, Supplement.1, " Debris Plugging of Emergency Core Cooling Suction Strainers"

Reference:

NRC Bulletin 93-02, Supplement 1 File: A-101a

Dear Mr. Russell:

On February 18, 1994, the NRC issued Supplement 1 to Bulletin 93-02, " Debris Plugging of Emergency Core Cooling Suction Strainers." This supplement requests licensees Lo take interim actions to enhance the capability to prevent or mitigate the loss of Emergency Core. Cooling Systems (ECCS) due to strainer clogging following a Loss of Coolant Accident (LOCA). The supplement requests the submittal of a written report describing planned actions along with a schedule for completion of'these actions.

We have reviewed the bulletin supplement. Our interim actions to ensure ECCS reliability are described in the attachment. As requested in the supplement, the interim actions will be completed by May 19, 1994. We will submit a report confirming completion of these actions within 30 days of their completion.

Should you have any questions regarding this matter, please contact this office.

9404290035 940419 /

PDR ADOCK 05000331 O PDR_ /gj/l General Office

• P.O. Box 351

• C+ Mar Rapios, lows. 52406

• 319/398-4411 An IES INDoSTRIES Company I

, 8 Mr. William'T. Russell NG-94-1391 April 19, 1994 Page 2 This letter is true and accurate to the best of my knowledge and' belief.

IES Utilities Inc.

l By '/V9

' _/ John F. F*ranz/

Vicd President, Nuclear .

• State of Iowa ,

(County) of Linn Signed and sworn to before me on this

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1994, by r

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Notary P'b fc"in 'and'for\the State of Iowa

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JFF/CJR/pjv' Attachment cc: C. Rushworth L. Liu L. Root 4 R. Pulsifer (NRC-NRR)

J. Martin (Region III)

NRC Resident Office DCRC I

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- Attachment to

, NG-94-1391 Page1 IES Utilities Inc. Response to NRC Bulletin 93-02, Supplement 1 NRC Requested Interim Action Provide training and briefings to apprise operators and other appropriate emergency response personnel of the information contained (in Supplement 1] and in the referenced information notices regarding the potential for suppression pool strainer -

clogging.

DAEC Response

1. All licensed operators and on-shift shif t technical advisors (STAS) have been briefed on the potential for Emergency Core Cooling Systems (ECCS) suction ,

strainer clogging as discussed in NRC Bulletin 93-02,.. Supplement 1.

2. NRC Bulletin 93-02, Supplement 1 has been placed in operations required reading to allow operators to gain a better understanding of the suction strainer clogging phenomena.

3. Formal classroom training is being conducted during Licensed Operator Requalification Training Cycle 2 which began on March 28,1994. All STAS also attend this training which _ includes reviews of:

the Boiling Water Reactor Owners' Group (BWROG) guidance on indications and operator response to ECCS suction strainer clogging

. how to determine if adequate net positive suction head (NPSH) exists for the ECCS pumps; how the symptoms of a loss of NPSH due to strainer clogging

, would differ from the symptoms of a loss of NPSH due to other causes

- the different systems available to inject water into the Reactor Pressure Vessel (RPV).

- 4. Briefings have been conducted with appropriate members of the Emergency _

Response Organization to apprise them of the potential for ECCS suction strainer clogging, possible indications of clogging, and possible actions to mitigate strainer clogging.

i s

k 1

' Attachment to

. NG-941391 Page 2 NRC Requested Interim Action Assure that the emergency operating procedures make the operator aware of possible indications of ECCS strainer clogging and provide guidance on mitigation.

DAEC Response The DAEC EOPs and EOP Support Procedures have been reviewed and confirmed to be adequate to mitigate an ECCS suction strainer clogging event should it occur.

If a loss of ECCS occurs due to suction strainer clogging (or for any other reason),

the operators will use alternate water sources as necessary to restore and maintain RPV level and flood the RPV and/or containment.

NRC Requested Interim Action Institute procedures and other measures to provide compensatory actions to prevent, delay, or mitigate a loss of available NPSH 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:

. Reduction of flow (consistent with delivering the required ECCS flow) through the strainers to reduce head loss and extend the time for debris deposition Operator realignment of existing systems to allow backflushing of clogged strainers Operator realignment of existing systems to allow injection to the core from water sources other than the suppression pool Intermittent operation of the containment sprays, when possible, to reduce the transport of debris to the strainers

. Other plant-specific measures which assure availabil!'y of sufficient core and containment cooling to meet the design basis of the plant.

I i

U

, , o ANachment to

. NG-94-1391 Page 3 DAEC Response

1. The DAEC procedures currently allow the operators to reduce ECCS flows following a LOCA provided that they can maintain RPV water level. This reduction in tiow may reduce the head loss across the strainers and may extend the time for debris deposition.

2. The core spray system at DAEC is capable of being aligned to the condensate storage tanks (CSTs) as an alternate, water. source. The method to realign core .

, spray to the CSTs is currently contained in DAEC procedures. Therefore, if the.

core spray strainers clog, an alternate source of water is available.

3. The DAEC EOPs currently direct the use of other injection systems if the ECCS systems are incapable of providing adequate core cooling. These other systems include feedwater, condensate, control rod drive, residual heat removal service water and standby liquid control. These systems can be aligned by operator action in the Control Room. In addition, fire water, well water, general service water, emergency service water and condensate service water can be used to provide core cooling. These systems would be lined-up with operator action outside of the Control Room.

4. We have identified several possible methods for backflushing the ECCS suction

. strainers. These methods are being reviewed to assess the practicality of their use in a post-LOCA environment. We will provide the results of this review in the report confirming completion of our actions.

5. The strainer blockage incident at Barseback was compounded by the automatic initiation of containment spray. At DAEC, the containment spray function is not automatic. It will only be initiated when directed by EOPs. In addition, the system is interlocked to automatically secure when drywell pressure is reduced to a preset value.

6. The DAEC is currently revising its housekeeping procedures to assure continued containment cleanliness. These procedures will minimize the potential for other debris fouling the ECCS suction strainers.-

7. The DAEC will perform suppression pool cleanup and desludging during refueling outage 13. This cleanup will continue our program of minimizing the effect of  !

corrosion products and other particulates on strainer head loss.

8. We will continue to work with the BWROG in developing long term solutions to .

resolve the issue. 1

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