ML18192A078

R. E. Ginna - Steam Generator Inspection Final Report, May 11, 1977

ML18192A078
Person / Time
Site:	Ginna
Issue date:	05/11/1977
From:	Rochester Gas & Electric Corp
To:	Office of Nuclear Reactor Regulation
References
Download: ML18192A078 (10)

Text

Ginna Station Steam Generator Inspection Hay ll, 1977 Rochester Gas and Electric Corporation performed a planned inspection of Ginna Station steam generators from April 16, 1977 through April 23, 1977 in accordance with the Inservice 'Inspection Program as part of the annual refueling and maintenance outage.

This inspection consisted of eddy current examinations at 400 KHz and 100 KHz to detect defects from corrosion, or cracking, 400 KHz for dent evaluation, 25 KHz fo'r sludge profiling and 3.5 KHz to verify support plate integrity.

The inspection included the following:

Leq Tubes Concern ~Su art A-Inlet 195 25 KHz Sludge 1st 1731 400 KHz Defect 1st 148 400 KHz Defect 6th 125 400 KHz Defect U-bend 100 400 KHz Dent 6th 207 3.5 KHz Supports 6th 60 100 KHz Defect U-bend A-Outlet 195 25 KHz Sludge 1st 268 400 KHz Defect 6th 100 400 KHz Dent 6th 207 3.5 KHz Supports 6th

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Lece Tubes Concern ~suu ore B-Inlet 195 25 KHz Sludge 1st 1252 400 KHz Defect 1st 148 400 KHz Defect 6th 125 400 KHz Defect U-bend 70 400 KHz Dent 6th 100 3.5 KHz Support 6th 60 100 KHz Defect U-bend B-Outlet 195 25 KHz Sludge 1st 208 400 KHz Defect 6th 100 400 KHz Dent 6th 100 3.5 KHz Support 6th Results of these examinations are given in Figures 1 through 3 wnich includes the "A" inlet and the "B" inlet and outlet, respectively. Tables (1) and (2) of this report are included for comparison of the last five steam generator inspections.

All of the eddy current indications were within the first few inches of tubing directly above the tube sheet with the ex-ception of one in the U-bend area of the "B" steam generator.

This indication in th'e "B" steam generator U-bend area was on a periphery tube and appears to be a one-of-a-kind construction-type defect of very small volume, 95% through the tube wall.

The other indications with the exception of two, are postulated to be due to wastage, based on growth rates. The excepted two 2

tubes, in the "A" inlet, due'o their large growth rate compared to the mean, may have been caused by concentrations of caustics.

Confirmation of. this is not possible since the eddy current examination method cannot differentiate between indications resulting from either wastage or stress corrosion cracking, but can accurately measure the maximum defect penetration to within normal statistical variation. The indications are seen only in those areas 'where indications have 'been previously noted, with the exception of the indication in the "B" steam generator U-bend area.

There has been no expansion of the indication region to other areas of the steam generators. This inspection verified that there are not any other tubes with ID Indication in the periphery tubes associated with the wedge areas where there had, been a leak in April 1976 (see Licensee Event Report. 76-15).

The dent evaluation program performed on both steam generators revealed no dents above 10 mils with only a few of the tubes in each generator being involved. Along with the dent. evaluation program, a support plate integrity examination was performed which did not reveal any problems.

The small number of tubes in the "A" inlet which have experienced deterioration, inconsistent with the average, are believed to have deteriorated from the concentration of residual phosphates in the secondary side sludge deposits. These concentrations of phosphates are caused by the remaining traces of sludge deposits formed during the period of phosphate control of the secondary system water chemistry before the conversion to AVT chemistry control in November 1974.

Removal of residual phosphates from the secondary side over the, past 31 months of operation has been accomplished by continuous steam generator blowdown and high pressure water lancing. The high pressure water lancing performed on the secondary side is designed to remove as much of the sludge as possible, which contains the undesirable residual phosphates and/or caustics.

Blowdown samples taken during normal operation indicated only small amounts of phosphates present, although phosphates in the sludge could revert back into PO  : and concentrate on the tube surfaces which, depending on the molar ratio, would result in acidic or caustic attack of the tube.

The corrective action taken to ensure the continued reliability of the steam generators includes the following:

a. All tubes with eddy current indications of wall penetra-tion greater than or equal to 40% were plugged.

b. A thorough lancing of the secondary side of the tube sheets was performed in both steam generators to remove as much as possible any remaining phosphates and/or caustics con-tained within the sludge. Sludge lancing of both steam generators will be continued in an effort, to keep sludge content to a minimum. The lancing, coupled with blowdown during startup and normal .operation, should considerably reduce the probability of significant tube degradation during the plants'ubsequent operation.

c. In addition, a modification of the plant's secondary condensate system is under construction which is de-signed to insure that the feedwater entering the steam generators will be of the highest purity. This modifi-cation will add in-line demineralizers to the condensate system, and is scheduled to be placed in service in August of this year.

Because it has been established that all but 14 tubes from

'oth steam generators had less than 40% defect indications; because there were only a few tubes which experienced comparatively rapid degradation; and because sludge lancing should further reduce the probability of phosphate and caustic pockets forming, the steam generators are considered acceptable for uninterrupted use until the planned refueling outage in the Spring of 1978, approximately 1 year from the expected date of return to service of Ginna Station.

An eddy current examination of the steam generators in accordance with the Inservice Inspection Program shall be performed during the 1978 refueling outage.

TABLE (1)

STEAM GENERATOR INDICATION EXAMINATION DATE POSITXON SXZE (8) FEB. 1974 NOV. 1974 MAR. 1975 FEB. 1976 APR. 1977 20 329 631 655 230 730 20-24 63 59 109 59 39 II A II 25-29 50 46 63 47 37 30-34 36 31 38 50 23 INLET 35-39 14 25 27 31 8 40-44 24 14 22* 19* 0 45-49 12 5 14* 8* 11*

> 50 17* 2+ 10* 12* 2*

Total "A" Xnlet Tubes Examined 3260 1655 2174 3192 2003 At Each Inspection at 400KHZ STEAM GENERATOR INDICATXON EXAMXNATION DATE POSITXON SIZE(8) FEB. 1974 NO%...1974 MAR. 1975 FEB. 1976 APR. 1977 II A II 20 58 278 10 113 OUTLET 20 0 0 0 0 Total "A" Outlet Tubes Examined 430 442 3192 268 At Each Inspection at 400KHZ

• tubes were explosively plugged

TABLE (2)

STEAN GENERATOR INDICATXON EXhHXNATION DATE POSXTION SIZE(%) FEB. 1974 NOV. 1974 MAR. 1975 FEB. 1976 APR. 1977 20 21 490 411 764 719 20-24 4 3 13 25 12 IIBII 25-29 2 4 10 8 8 30-34 0 1 9 9 0 INLET 35-39 0 1' 5 3 1 40-44 0 ]* 1* 0 45-49 0 0 0 ".0 '*

0 50 0 0 ] 0*

Total "B" Inlet Tubes Examined 1098 675 1931 3247 1525 At Hach Inspection at 400 KHZ STEAM GENERATOR INDXCATXON EXAMINATION DATE

.POSITION SIZE (%) FEB. 1974 NOV. 1974 MAR. 1975 FEB. 1976 ,APR. 1977 II Bll 20 0 1003 90 OUTLET 20 0 2 1*

Total "B" Outlet Tubes Examined 516 442 3247 268 At Each Inspection at 400 KIIZ NOTE: Two tubes in the "B" steam generator were explosively plugged in January 1976 and fifteen in April 76

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