ML20086S317

AO-S1-74-15:on 741219,abnormal Degradation Found of One of Several Boundaries Designed to Contain Radioactive Matls Resulting from Fission Process.Caused by Sheet Sludge Deposits & Deleterious Effects of Sodium Phosphate Control

ML20086S317
Person / Time
Site:	Surry
Issue date:	01/23/1975
From:	Stallings C VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	Moseley N NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
References
AO-S1-74-15, NUDOCS 8403010504
Download: ML20086S317 (6)

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y  % ,w; Mr. Norman C. Moseley, Director Serial No. '40)<'};7}ThN Directorate of Regulatory Operations POIJi/JTB:c1w United States Atomic Energy Commission Region II - Suite 818 Docket No. 50-280 230 Peachtree Street, Northwest License No. DPR-32 Atlanta, Georgia 30303

Dear Mr. Moseley:

Pursuant to Surry Power Station Technical Specification 6.6.B.1, the Virginia Electric and Power Company hereby submits forty (40) copies of Abnormal Occurrence Report No. A0-S1-74-15.

The substance of this report has been reviewed by the Station Nuclear Safety and Operating Com:nittee and will be placed on the agenda for the next meeting of the System Nuc1 car Safety and Operating Conunittee.

Very truly yours,

. ((/, ydfd/M-C. M. Stallings Vice President-Power Supply and Production Operations Enclosures 40 copies of A0-SI-74-15 cc: Mr. K. R. Coller, Assistant Director for Operating Reactors

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O O ABNORMAL OCCURRENCE REPORT REPORT NO. A0-SI-74-15 STEAM GENERATOR TUBE DETERIORATION DECEMBER 26, 1974 DOCKET NO. 50-280 LICENSE NO. DPR-32 SURRY POWER STATION VIRGINIA ELECTRIC AND POWER COMPANY l

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. U V I. INTRODUCTION In accordance with Technical fpecification 6.6.B.1 for Surry Power Station, Operating License Number DPR-32, this report describes an abnornal occurrence which was noted on December 19, 1974. The Directorate of Regulatory Operations, Region II, was notified on December 19, 1974.

The occurrence reported herein is classified as an abnormal occurrence pursuant to Technical Specification 1.0.I.4 which states that "An abnormal occurrence is defined as: Any abnormal degradation of one of the several boundaries which are designed to contain radioactive materials resulting from the fission process."

Results of eddy current testing to date for Surry steam generators indicate tube wall deterioration in excess of 50 per cent in 195 tubes.

II.

SUMMARY

OF OCCURRENCE Eddy current inspections per Regulatory Guide 1.83 have recently been completed on all three Unit No. I steam generators. Eddy current inspections have previously been completed at various times prior to the implementation of Regulatory Guide 1.83 at Surry Power Station. Special Report SR-SI-74-05 reported the results of these earlier inspections.

To date eddy current wall thickness data has been taken on the hot leg side of 10,881 tubes and the cold leg side of 1689 tubes. Table I shows the number of tubes per steam generator that have been inspected for wall thickness deterioration. To date, 195 tubes have shown wall thickness deterioration of >50 per cent. As a result of these data, 58 tubes in Unit No. 2 have been plugged, and 137 tubes in Unit No. 1 are being plugged during the current refueling outage. Two tubes in Unit No.

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. O 1 "B" steam generator had been previously plugged af ter removal for destructive testing. After current plugging operations are complete, a total of 197 tubes will be plugged in the steam generators of the two (2) units. Table II shows the number of tubes per steam generator that will be plugged.

III. ANALYSIS OF OCCURRENCE Tube wall deterioration in the steam generators can be attributed to tube sheet sludge deposits and deleterious effects of sodium-phosphate chemistry control. This phenomena is a generic problem and additional investigation is in progress to further understand it.-

IV. CORRECTIVE ACTION TO PREVENT RECURRENCE The initial corrective action being. taken is to ' plug all tubes showing a tube wall thickness deterioration of >50 per cent.

In order to prevent recurrence, the steam side chemistry control-is being changed from phosphate treatment to all volatile treatment. -An AVT specification i.

has been provided by the nuclear steam supply system manufacturer, the Westinghouse Electric Corporation. All volatile treatment was initiated

'during start-up of Unit No.1 2 on January 3, 1975,'and it will be initiated on Unit No. I during: start-up following.the current refueling outage.

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.V. ANALYSIS AND EVALUATION- 0F SAFETY IMPLICATIONS OF' THE OCCURRENCE The plugging of. tubes in the: steam. generators has resulted'in'a-reduction'of available heat; transfer area. Table III lists the per cent l ,

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. O O reduction of heat transfer area in each steam generator. These figures represent an insignificant reduction of steam generator heat transfer area.

s The deterioration of steam generator tube wall material in the steam generators has only slightly degraded the integrity of the reactor coolant boundary. However, the plugging of all steam generator tubes with wall thickness 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 conditions for a main steam line break or a LOCA. Thus the criteria for steam generator tube strength, as established by the nuclear steam supply system manufacturer, the k'estinghouse Electric Corporation, has not been violated. Therefore, there are no safety implications associated' with this occurrence.

s VI. CONCLUSIONS The licensee concludes that:

1. The deterioration of the tubes has been primarily caused by the sodium-phosphate chemistry control.

2. Sodium-phosphate treatment has been replaced by all volatile treatment on the steam side of both units.

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3. The occurrence described herein did not affect the safe operation of the station.

4. The occurrence described herein did not adversely affect the health or safety of the general public.

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. oJ TABLE I TOTAL NUMBER OF STEAM GENERATOR TUBES INSPECTED FOR WALL TillCKNESS DETERIORATION UNIT NO. 1 A B C Hot Leg 3272 2875 1514 Cold Leg 580 545 84 UNIT NO. 2 Hot Leg 1192 1002 1026 Cold Leg 468 12 0 TABLE 11 NUMBER OF TUBES PLUGGED Unit No. 1 55** 2* 82**

Unit No. 2 15** 33** 10**

• Two tubes plugged in Unit No. 1 "B" steam generator due to tube removal for destructive testing.

• • Tubes plugged due to hot leg flaw indications.

TABLE III PERCENT REDUCTION OF HEAT TRANSFER AREA IN STEAM GENERATORS Unit No. I 1.63% .06% 2.43%

Unit No. 2 .44% .98% .30%

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