ML20086S280

SR-S1-74-05:deterioration of Steam Generator Tubes Noted. Caused Not Determined.Sludge Deposits & Deleterious Effect of Sodium Phosphate Chemistry Control Contributed to Magnitude & Rate of Deterioration

ML20086S280
Person / Time
Site:	Surry
Issue date:	11/29/1974
From:	Stallings C VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	Moseley N NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML20086S284	List: ML20086S280 ML20086S297
References
SR-S1-74-05, NUDOCS 8403010482
Download: ML20086S280 (9)

Text

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,AlI. Y k RN VinosqtA Er.ncrusc Axo Powna COMI*AN,

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November 29, 1974 C.g _:

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k! i fiV Mr. Norr.an C. Mseley, Director Serial No. 342 Directorate of Cagulatory Operations POLM/JTB:c1w United States Atomic Energy Cocnission Region II - Suite 818 Docket Nos. 50-280 230 Peachtrea Street, Northwest 50-281 Atlanta, Georgia 30303 License Nos. DPR-32

, DPR-37 Dest lir. lioseley:

Pursuant to Surry Power Station Technical Specification 6.6.B.1, the Virginia Electric and Pcwcr Co=pany hereby submits forty (40) copies of Special Report No. SR-SI-74-05.

The substance of this report has been reviewed by the Station Nuclear Safety and Operating Conmittee and will bo placed on the agenda for the next

nceting of the Systcu 1ucicar Safety and Operating Cc=nittoa.

Very truly yours, s &'W

/V C. M. Stallinis (

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/ cad Ir< ' cia o "ratiwa Enclouuro SR-SI-74-05 cc lir. K. R. Coller/ *

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8403010482 741129 PDR ADOCK 05000200 S PDR 122Ei i

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! SPECIAL REPORT

! SR-S1-74-05 I

i STEAM GENERATOR TUBE DETERIORATION -

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DOCKET NOS. 50-280 50-281 LICENSE NOS. DPR-32 DPR-37 j OCTOBER 31, 1974 i

1 I SURRY POWER STATION -

j VIRGINIA ELECTRIC AND POWER COMPANY k

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'I. INTRODUCTION i-This report is written at the request of the U.S. Atomic Energy a

Commission, Directorate of Regulatory Operations. Region II. It is i

intended to provide information regarding the deterioration of steam i

generator tubes in Unit Nos. I and 2 at the Surry Power Station.

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! Although tube deterioration in PWR steam generators at other operating facilities has been discovered, this report will address only the problem at the Surry Power Station.

The cause and effect relationship between steam generator design, chemistry control and tube deterioration is not fully understood. However, the Virginia Electric and Power Company has instituted programs to in-vestigate both the magnitude of and causes for tube deterioration in the 4

Unit Nos. 1 and 2 steam generators at the Surry Power Station.

, Corrosion performance tests performed by the Westinghouse Electric a

Corporation have shown that sodium-phosphate treatment of steam generator water contributes to the deterioration of steam generator tubes. This

< fact has been verified by operational data on several operating reactors.

i II. DISCUSSION Eddy current ' inspections have been performed on four (4) of six (6)

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steam generators installed in Unit Nos.1 and - 2 in accordance with ' Regulatory -

Guide 1.83. Eddy current data has been taken on the hot leg side of '4891

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tubes and the' cold leg side cf _986 tubes. Sections of two (2) steam generator U-tubes rhowing' indications of deterioration were' removed forL

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. , , \ V destructive testing. Table I shows the number of tubes per steam generator that have been inspected for wall thickness deterioration. As a result of the eddy current inspection data, 58 steam generator tubes have been plugged. All plugged tubes showed a wall thickness reduction of 50 per cent or greater from the original design dimension. Plugging of tubes with wall deterioration of >50 per cent provides reasonable assurance that no tube wall with more than 75 per cent reduction will be subject to the worst combination of loading cenditions for a main steam line break or a LOCA. This satisfies the design criteria for steam generator tube wall strength. The removal of tube sections for destructive testing resulted in the need to plug four (4) tube sheet penetrations in Unit 1 loop B steam generator. Therefore, there are a total of 60 tubes plugged in steam generators at Surry. Table II shows the number of tubes per steam generator that have been plugged.

Additional eddy current tests have been performed on four (4) steam generators to determine the presence of secondary side sludge deposits above the tube sheet region. Sludge deposit data has been taken on the hot leg side of 628 tubes and the cold leg side of 116 tubes. Table III shows the number of tubes per steam generator that have been inspected for sludge deposits. Table IV shows the range of sludge deposit data for the steam generators inspected.

Inspection reports describing the procedural details of all testing performed and individual tube data are available onsite.

Subsequent to the acquisition of the above data, Unit 1 loop A steam generator developed a tube leak of unknown origin.

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III. CONCLUSIONS All of the reasons for tube wall deterioration in Surry steam generators have not been determined. However, sludge deposits and the deleterious effect of sodium-phosphate chemistry control contribute to the magnitude and rate of deterioration. Programs have been instituted at Surry to remove steam generator sludge depesits and to commence all volatile treat-ment of steam generator water. It is expected that these actions will significantly reduce tube deterioration in Surry steam generators.

Tube plugging and tube wall deterioration bave not seriously affected reactor safety. The design criteria for tube wall strength has not been violated, and the reduction in heat transfer area of any steam generator due to tube plugging does r.ot exceed 1 per cent.

Virginia Electric and Power Company has commenced a eurveillance program in accordance with Regulatory Guide 1.83 to review this problem on a routine basis.

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TABLE I a

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4 NUMBER OF STEAM GENERATOR TUBES INSPECTED FOR WALL TilICKNESS DETERIORATION

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, s A B C 1, i s llot Leg 0 1671 0 1 Cold Leg 0 506 0 s

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UNIT NO. 2 A B C llot Leg 1192 1002 1026 Cold Leg 468 12 0

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. . . O O TABLE II NUMBER OF TUBES PLUGGED A B C Unit No. 1 0' 2* O Unit No. 2** 15 33 10

• Two tubes plugged in 1B steam generator due to tube removal for destructive testing.

• • All tubes plugged in Unit No. 2 steam generators due to hot leg flaw indications, y

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1 TABLE III j

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I NUMBER OF TUBES INSPECTED (i FOR SLUlX;E DEPOSITS f

UNIT NO. I r A B C f Hot Leg 0 227 0 Cold Leg 0 0 0 t

t UNIT NO. 2 A B C Hot Leg 169 116 116 Cold Leg 116 0 0

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, TABLE IV SLUDGE HEIGHT E0VE TUBESHEET i

UNIT NO. 1

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Max. - 8" -

Avg. - 1.4" -

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i A** B* C i Min. 0" (0") 0" 0" Max. 2" (4.5") 1.5" -3.5"

.4" (1.7") .3" Avg. . 5

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• Hot Leg only inspected

• • Cold Leg data shown in parenthesis

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