ML18038B058

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

ML18038B058
Person / Time
Site:	Browns Ferry
Issue date:	12/01/1994
From:	Salas P TENNESSEE VALLEY AUTHORITY
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
IEB-93-002, IEB-93-2, NUDOCS 9412080139
Download: ML18038B058 (14)

Text

~ PR.IC3R.I EY' (ACCELERATED RIDS PROCESSIi REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)

ACCESSION NBR:9412080139 DOC.DATE: 94/12/01 NOTARIZED: NO FACIL:50-260 Browns Ferry Nuclear Power Station, Unit 2, Tennessee AUTH.NAME AUTHOR AFFILIATION SALAS,P.

Tennessee Valley Authority RECIP.NAME RECIPIENT AFFILIATION Document Control Branch (Document Control Desk)

SUBJECT:

Forwards suppl response to NRC Bulletin 93-002,Suppl 1,

"Debris Plugging of Emergency Core Cooling Suction Strainers."

DISTRIBUTION CODE:

IE11D COPIES RECEIVED:LTR ENCL SIZE:

TITLE: Bulletin Response (50 DKT)

NOTES:

DOCKET 05000260 RECIPIENT ID CODE/NAME PD2-4-PD INTERNA~~ILE CENTER 02 NRR/DORS OGCB NRR/DSSA NRR/DSSA/SRXB NRR/SCSB RGN2 FILE 01 EXTERNAL: NOAC COPIES LTTR ENCL 1

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RECIPIENT ID CODE/NAME WILLIAMS,J.

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1 NOTE TO ALL'RIDS"RECIPIENTS:

PLEASE HELP US TO REDUCE iVASTE!CONTACTTHE DOCL'CLIENT CONTROL DESK. ROOiA I Pl-37 (EXT. 5N-2083 ) TO ELIXIINATEYOL'R NAME FROil DISTRIBUTIONLISTS I'OR DOC!.'MENTS YOU DON"I'EED!

TOTAL NUMBER OF COPIES REQUIRED:

LTTR" 15 ENCL 15

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Tennessee Valley Authority. Post Office Box 2000. Decatur. Alabama 36609 December 01, 1994 U.S. Nuclear Regulatory Commission ATTN:

Document Control Desk Washington, D.C.

20555 Gentlemen:

In,the Matter of

)

Tennessee Valley Authority

)

Docket No. 50-260 BROWNS FERRY NUCLEAR PLANT (BFN) UNIT 2 SUPPLEMENTAL

RESPONSE

TO NRC BULLETIN 93-02'UPPLEMENT 1

DEBRZS PLUGGING OF EMERGENCY CORE COOLING SYSTEM (ECCS)

SUCTION STRAINERS This letter.supplements TVA's April 18,

1994, response to Bulletin 93-02, Supplement 1.

TVA's original response stated that there were no temporary or permanently installed'ibrous air filter or other sources of fibrous material not designed to withstand a loss of coolant accident in Unit 2.

Since that time, TVA has identified permanently installed asbestos, calcium silicate and fiberglass insulation in nine Unit 2 drywell penetrations.

This insulation is located between the pipe and the penetration sleeve.

A description of the background of.this issue and details regarding the amount and location of the fibrous insulation is provided in the enclosure to this letter.

TVA understands the importance to plant safety of the ECCS suction strainer blockage issue.

TVA's design features, the augmenting of the operator's required reading program,'nhanced classroom and simulator training, revised BFN

'mergency Operating Instructions appendices, and updated design control procedure are considered adequate to assure continued ECCS suction capability.

TVA will=continue to participate in the ongoing work of the Boiling Water Reactor Owners'roup (BWROG)

ECCS Suction Strainers Committee and the BWROG Emergency Procedure Committee.

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'tt412080159 941201 PDFl ADOCK 0500026 0 Q

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U.S..Nuclear Regulatory Commission Page 2

December 01, 1994 There are no commitments contained in this letter.

If'ou have any -questions, contact telephone me at (205) 729-2636.

Since Pedro Salas Manager of Site Licensing Enclosure cc:

see page 3

0

U.S. -Nuclear Regulatory Commission Page 3

December Ol, 1994 cc (Enclosure):

Mr. Mark S. Lesser.,

Section Chief Division of-Reactor Projects U.S. Nuclear Regulatory Commission Region II 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323 NRC Resident.Inspector Browns Ferry Nuclear Plant Route 12, Box 637

Athens, Alabama 35611 Mr. J.

F. Williams, Project Manager U.S. Nuclear Regulatory Commission One White Flint, North 11555 Rockville Pike Rockville, Maryland 20852

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ENCLOSURE TENNESSEE VALLEY AUTHORITY BROWNS FERRY NUCLEAR PLANT (BFN)

UNIT 2 SUPPLEMENTAL RESPONSE TO NRC BULLETIN 93-02'UPPLEMENT 1

DEBRIS PLUGGING OF EMERGENCY CORE COOLING SUCTION STRAINERS BACKGROUND On May 11,

1993, NRC issued Bulletin 93-02 (Reference 1), which notified licensees of a previously unrecognized contributor to the potential loss of net positive suction head (NPSH) for the Emergency Core Cooling Systems (ECCS) during the recirculation phase of a loss of coolant accident (LOCA).

The filtering of corrosion products, dust, fibrous thermal insulation, debris, and other temporary material may cause an unexpectedly rapid loss of net positive suction head for the ECCS pumps when they are needed to perform their intended function.

Licensees were requested to identify fibrous air filters or other temporary sources of fibrous material, not designed to withstand a LOCA, which are installed or stored within the primary containment and take prompt action to remove any such material.

TVA responded to Bulletin 93-02 on May 23, 1993 (Reference 2).

Each Browns Ferry unit is a BWR 4 with a Mark I containment.

TVA performed a walkdown of the Unit 2 drywell (primary containment) and confirmed that there are no temporary fibrous air filter or other sources of fibrous material not designed to withstand a

LOCA.

BFN Units 1 and 3 are shutdown for extended outages.

TVA committed to evaluate these units for permanent fibrous material and to inspect and remove temporary fibrous material prior to, their respective startups.

On February 18,

1994, NRC issued Supplement 1 to Bulletin 93-02 (Reference 3).

The staffs'ngoing review of this issue suggests that the previous method of estimating the fragmentation of insulation materials may not be representative of the large break LOCA scenario and that the extent of debris generation due to a jet from a postulated pipe break may have been underestimated.

In addition, small particles, in combination with debris fibers, have been found to significantly increase the pressure drop across strainers.

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TVA's original response to Supplement 1 of the Bulletin was provided on April 18, 1994 (Reference 4).

This response stated that there were no temporary or permanently installed fibrous air filter or other sources of fibrous material not designed to withstand a LOCA.

The BFN design features (suction ring header and inter-unit Residual Heat Removal system cross connect capability) coupled with TVA's commitments to augment the operator's required reading program, conduct classroom and/or simulator training, revise appendices in the BFN Emergency Operating Instructions, and change the applicable design control procedure were considered additional defense in depth measures against potential debris blockage of the ECCS strainers.

By letter dated July 19, 1994 (Reference 5),

NRC stated that TVA's response adequately addressed the actions necessary to assure continued ECCS suction capability..

On July 29, 1994 (Reference 6),

TVA notified NRC that the commitments contained in TVA's April 18, 1994 response to Bulletin 93-02, Supplement 1,

were complete.

DESCRIPTION OF PERMANENTLY INSTALLED FIBROUS MATERZAL INSIDE THE DRYWELL BFN primarily uses half cylinder reflective metallic insulation in the drywell.

One approximately two square foot piece of encapsulated fibrous insulation is used for thermal protection of a cable.

In addition, approximately 190 ft'f asbestos, 35 ft'f fiberglass, and 8 ft~ of calcium silicate (which is 95 percent non-fibrous) insulation is used in drywell penetrations.

This insulation is located between the pipes and the penetration sleeves.

A typical sketch of a penetration, which shows the location of this insulation, is provided as an attached figure.

CONCLUSION TVA understands the importance to plant safety of the ECCS

,suction strainer blockage issue.

TVA's design features, the augmenting of the operator's required reading program, enhanced classroom and simulator training, revised BFN Emergency Operating Instructions appendices, and updated design control procedure are considered adequate to assure continued ECCS suction capability.

TVA will continue to participate in the ongoing work of the BWR Owners'roup (BWROG)

ECCS Suction Strainers Committee and the BWROG Emergency Procedure Committee.

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