ML20086S317
| 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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VIHOINIA ELECTRIC AND Powen CourAny H uomin own.Vx noxx x A nonal g',- @. $'O,:',
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January 23, 1975
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. 1
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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
t I
, 7..
2 2_
.2
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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.
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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.
I' 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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O 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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