ML20057B706

Provides Suppl Response to NRC Bulletin 93-002, Debris Plugging of ECC Suction Strainers. Determined That Interim Solution Will Be to Remove Both Trains Containment Air Charcoal Filter Units pre-filters

ML20057B706
Person / Time
Site:	Catawba
Issue date:	09/16/1993
From:	Rehn D DUKE POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
IEB-93-002, IEB-93-2, NUDOCS 9309230165
Download: ML20057B706 (3)

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- DukehkerCompany D. L Rott l Cataw!ra Nuclear Genention De;>artment nce hesident  !

GnConcordRoad (803)S3133!5 0' lice j York, SC29745 (803)S313CUax i

. DUKEPOWER i

September 16,-1993 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555

Subject:

Catawba Nuclear Station, Units 1 and 2 Docket Nos. 50-413 and 50-414 NRC Bulletin 93-02, Debris Plugging of Emergency Core Cooling Suction Strainers Supplemental Response Duke Power Company's initial response to Bulletin 93-02 " Debris Plugging of Emergency Core Cooling Suction Strainers" for Catawba Nuclear Station was submitted by letter June 10,1993. The initial response concluded that the fibrous air filters permanently installed in Catawba Nuclear Station containments do not pose a potential to degrade the Emergency Core Cooling System (ECCS), therefore, no actions were required to assure the functional capability of the ECCS.

On September 8,1993, conversations with Nuclear Reactor Regulation (NRR) personnel provided additional concerns relative to debris plugging of ECCS Suction Strainers, in that fibrous filter material in the Containment Air Charcoal Filter Units ,

(CACFUs), located in lower containmer:t, may become granular in size and neutrally buoyant due to a direct leak impingement, :nigrate to the ECCS Suction Strainer and

" coat" the strainer, reducing net positive suction head to the Residual Heat Removal System (ND) Pumps used for recirculation following a Loss of Coolant Accident (LOCA).

Due to these additional concerns, we have determined that an interim solution will be to remove both trains' CACFU pre-filters and high efficiency particulate adsorbers (HEPAs) during the next shutdown on each unit (i.e. next forced outage or planned refueling outage). Appropriate work orders have been developed to accomplish these efforts during the next forced / refueling outage for both units.

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Additionally, since the next planned refueling outage for Unit 2 is currently scheduled l for April,1994, compensatory measures evaluated at other nuclear facilities to reduce l the probability for debris plugging of the ECCS Suction Strainers were evaluated for applicability to Unit 2. This evaluation determined that the following actions are viable, and will be developed as effective compensatory measures for Unit 2:

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• Upon changeover from injection to Recirculation Phase, if both trains of l the ECCS are available, operators will secure one (1) train of ECCS  !

recirculation to reduce the flow velocity to the ECCS Suction Strainer, I which will maximize not positive suction head available to the ECCS train in service.

• Measures are being developed to monitor ECCS pump performance for potential degradation due to strainer blockage. Additional methods are being developed to re-configure system alignments to clear blockage of '

the ECCS Suction Strainer.

These cornpensatory measures will be implemented on Unit 2 by October 30,1993 1 and will remain in effect until the Unit 2 CACFU pre-filters and HEPA filters are j removed from containment. l I

However, during the upcoming Unit 1 outage (currently scheduled to begin October 30, 1993), a visual inspection will be performed in Unit 1 lower containment to 1 identify high energy interactions which have a potential for a direct leak impingement on the CACFU filters. This is consistent with the actions taken by Duke Power's McGuire Nuclear Station. If this visualinspection does not identify a potential for high energy line interaction on the CACFU filters, like that found at McGuire Nuclear Station, an analysis will be performed and submitted to your staff as justification to re-install the filters. Otherwise, the work orders for both units and the Unit 2 compensatory actions will be left intact. i 1

i I declare under penalties of perjury that the statements set forth herein are true and  !

correct to the best of my knowledge.

Very truly yours, D.L. Rehn, Site Vice-President Catawba Nuclear Station

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U.S. Nuclear Regulatory Commission September 16,1993 Page 3 xc: S.D. Ebneter Regional Administrator, Region 11 R.E. Martin, ONRR R.J. Freudenberger Senior Resident inspector

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