ML17249A867

Forwards Apr 1980 Steam Generator Insp Rept & Evaluation of Results,In Response to NRC Request

ML17249A867
Person / Time
Site:	Ginna
Issue date:	04/29/1980
From:	White L ROCHESTER GAS & ELECTRIC CORP.
To:	Ziemann D Office of Nuclear Reactor Regulation
References
NUDOCS 8005050232
Download: ML17249A867 (19)

Text

REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)

ACCESSION NBR>>8005050232 DOC ~ DATE ~ 80/09/29 NOTARIZED:

NO DOCKET FACIL:50 200 Robert Emmet Ginna Nuclear Planti Unit li Rochester G

05000244 AUTH'AME AUTHOR AFFIL'IATION WHITEs L ~ D, Rochester Gas 8 Electric Corp.

REC IP, NAME RECIPIENT AFFILIATION Office of'uclear Reactor Regulation ZIKMANNgD,L ~

Procedures 5 Test Review Branch

SUBJECT:

Forwards Apr 1980 steam generator insp rept 8 evaluat'ion of resultsiin response to NRC request, DISTRIBUTION CODE:

A001S COPIES RECEIYKD:I TR I ENCL ~

SIZE:

TITLE: General Distr ibution fot after Issuance of Operating Lic

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ROCHESTER GAS AND ELECTRIC CORPORATION o

89 EAST AVENUE, ROCHESTER, N.Y. 14649 LEON D. WHITE. JR.

VICK PRKSIDKNT TKLKPHDNK

• RK*CDDK TIS,546-2700 April 29, 1980 Director of Nuclear Reactor Regulation Attention:

Nr. Dennis L. Ziemann, Chief Operating Reactors Branch No.

2 U.S. Nuclear Regulatory Commission Washington, DC 20555

Subject:

Steam Generator Inspection Results and Analysis R. E. Ginna Nuclear Power Plant, Unit No.

1 Docket No. 50-244

Dear Nr. Ziemann:

1 In,response to'a reguest of Dr., B. D. Liau'f your staff we are submitting for your information a report on the 1980 Steam Generator Inspection and an, evaluation of the results.

Please find attached one copy of each.

1 Attachment A - April 1980 Steam Generator Inspection Attachment B - Evaluation of Results Very truly yours, L. D. Whit

, Jr.

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Attachment A

A ril 1980 Steam Generator Ins ection A program of planned eddy cuirent examinations was conducted on both loop "A" and "B" steam generators at R. E. Ginna Nuclear Power Plant from April 3-8, 1980 during the scheduled refueling and maintenance outage.

The purpose of these examinations was to assess the integrity of the steam generator tubing and take cor-rective actions to assure reliable and safe operation during the next operating fuel cycle.

These examinations consisted of a multifreguency eddy current examination to detect and measure potential tube defects.

This is the third year of multifrequency eddy current. examinations at the Ginna plant.

The four frequencies chosen were as follows:

a.

400 KHz Differential, b.

200 KHz Differential, c.

100 KHz Differential, d.

100 KHz Absolute.

Along with the four freguencies, a support plate and tube sheet mix was utilized by combining the inputs from the 400 KHz and 200 KHz differential frequencies.

This mix allowed for more accurate in-terpretation of signals from areas of the steam generator where the signal from support structures interfere with signals generated from tubing flaws.

The examinations consisted of a 100 percent inspection of both steam generators inlets and the outlets receiving approximately a 25 percent inspection.

Minimum tube length examined was from the first.

support plate down through the tube sheet crevice.

Tubes were also examined over the U-bend region and to the sixth support, plate.

With N

the exception of indications which will be discussed in the text,

1

there were not any subtle changes noted over previous years data.

The steam generator outlets did not show any reportable indications.

In the "A" steam generator inlet, only one tube (R 16 C 88) requiring plugging was found. It displayed a

50% small volume indication 2

inches above the top of the tube sheet.

The "B" steam generator, which had two (2) crevice indications in April of 1979 and eleven (ll) crevice indications in the De-cember 1979 showed thirty one (31) crevice indications at this time.

These indications fall into two categories, the first being 13 indi-cations which were identified at all examination frequencies and are as follows:

R17C35 R18C35 R18C36 R14C38 R17C40 R17C41 R15C41

- 38~ 15" above tube end

- <20%,

15" above tube end

- 48' 18" above tube end

- 58~ 15" above tube end

- 60~ 18" above tube end

- 60~ 18" above tube end

- 67~ 18" above tube end R15C42 R14C43 R19C44 R24C45 R24C46 R21C54

" 75~os 85~0 I

- 95 60~0/

15" above tube end 12" above tube end 10" above tube end 15" above tube end 15" above tube end 15" above tube end The second category included 18 indications that were detected with the 100 KHz absolute frequency only.

These indications were an abnormal vertical channel signal on the brush strip chart recorder that, resembled the signals at 100 KHz absolute of the 13 tubes found at the other frequencies.

Therefore, the following tubes are considered to be under crevice attack:

R14C32 R15C34 R16C34 R17C34 R18C34 R15C35 R16C35 R17C36 R16C37 R19C37 R18C38 R19C38 R13C39 R18C41 R15C44 R14C46 R18C46 R18C48 These 31 tubes with crevice indications, with the exception, of three

R24C45, R24C46 and R21C54, all fit. into a pattern with the previous 13 tubes found in the two examination in 1979, as shown

r

3 in Figures I and II.

In addition to these, three tubes in the "B" inlet were found with defects above the tube sheet as follows:

R32C16 - 41%, small volume indication, 2" above tube sheet R45C48 46%,

24" above tube sheet R45C47 36%, 24" above tube sheet.

After eddy current data analysis was complete crevice indications were identified only in the "B" steam generator inlet and not in the "A" steam generator.

Two tubes from the "B" steam generator inlet and one tube from the outlet were chosen.for tube pulling.

These tubes, R17C41 60% indication 18" above the tube

end, R15C44 - smallest 100 KHz absolute signal, and R17C40 out-let (cold leg) tube with no indication, but the opposite end of an inl'et tube with an indicator, were determined as tubes that would potentially give valuable information concerning the damage mechanism and also allow for three different crevices to have deposits removed for chemical analysis.

The tube pulling operations went as follows:

R17C41 60% indication 18" above tube end a ~b.

c d.

marked ID at 14", 24" and 26" from tube end tube started pulling at a force of 4500 psi then dropped to 2500 psi for short period of time, average remainder pulled at 1500 psi.

total length cut 69.5", total pulled length 72" giving approximately 2.5" elongation or 3.5%.

honed sample from crevice.

2.

R15C44 small 100 KHz absolute signal in crevice region a

~b.

c ~

d.

marked ID at 14", 24" and 26" from tube end tube started pulling at, a force of 2400 psi dropped to 1800 then increased for an average pull of 2100 psi total length cut, was 69.5", total pulled length 72.06" honed sample from crevice.

3.

R17C40 - No indication from outlet a.

marked ID at top of tube sheet.

b.

tube started pulling at a force of 3200 dropped to approximately 1100 for the remainder of the pull

c.

total length cut was 69.5", total pulled length 69.875".

d.

honed sample from crevice.

The proposed hypothesis for the crevice cracking mechanism is a general intergranular corrosion attack (IGA) that takes place down in the tube sheet crevice area.

After the intergranular corrosion attack has penetrated deep enough into the tube wall the remaining wall cracks due to stress caused either by pressure and/or thermal loads on the tube.

The active species involved in this attack is postulated to be a caustic solution of NaOH,

however, Na2S04, or NaSi03 may also be involved.

Crevice deposit analysis and the pulled tube surface deposit analysis should help identify the actual species involved in this attack.

This concentration of caustic is believed to be from previous phosphate chemistry operation

( prior to November 1974) and not to be fxom the all volatile treatment

( AVT) operating chemistry that Ginna has used the last five and one half years.

It is postulated that the molar ratio between Na and PO in the crevice has been in-4 creasing in the crevice as P04 has been slowly removed during wettings and subsequent dryouts.

This action leaves behind free Na and OH, which would raise the pH and produce caustic crevice conditions.

A number of actions have been taken to gain additional informa-tion concerning the cause of crevice intergranular 'corrosion attack and to reduce the propensity for cxevice attack.

These actions in-clude a more sophisticated eddy current inspection, tube pulling, tube sheet water lancing, cxevice flushing boil out, continued close control of secondary chemistry, and a mid-cycle Fall steam generator inspection.

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Our use of multifrequency eddy current, inspection including a 100 KHz absolute examination has allowed the identification and plugging of otherwise undetected attack within the crevice region.

Tubes which might. otherwise be susceptible to crack growth and result in primary to secondary leakage are plugged.

The three tubes which have been pulled and are being examined by Westinghouse Electric Corporation should yield valuable informa-tion concerning damage mechanism and chemical species.

As in all previous steam generator inspections, an extensive program of water lancing on the secondary side has been carried out.

Thus, the quantity of sludge in the secondary side is minimized.

A crevice flushing boil out procedure will be employed to further reduce the potentially detrimental material in the tube sheet, crevice.

The program to be employed at Ginna is based, in

part, on programs previously employed at Kansai Electric Power Company at Mehama Unit 2 and by Wisconsin Electric Power Company at Point Beach Unit 1.

The program at Ginna will involve approxi-mately twenty-two cycles.

Boric acid will be added during a number of these cycles with the objective of neutralizing the caustic solution in the crevices.

During startup and plant operation, the full.flow condensate demineralizers will continue to be used and careful control of secondary chemistry will be maintained.

Operating experience has demonstrated our ability to maintain excellent chemistry conditions on the secondary side.

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Finally, we plan to shut down Ginna Station in the Fall of 1980 to reexamine the steam generators.

This inspection should aid xn establishing the effectiveness of 'corrective actions being applied now and to planning any future corrective actions.

Figure I RG6E.steam genera,tor B Irllet Crevice Xnaxcatxons ql SSSlSSE6$ 797175757I I94745a34i&95755 S35I494745454I 393735333I 292725232l l9 I7 l5 l3 II 9 7 5

3 COLUMNS lo 7472 70 62 60 52S 44 42.

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March 79 2 k -December 79-ll NOZZLE=

4/25/80 ABC 1

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- Figure II RGaB st;earn GeoqraQgr B Inlet Crevice Indications Rl 898785%6I 791175757I 1947 45l 341 6957 55 535I49474545 4I 3937 35333I 292725232I IQ I7 l5 l3 I I 9 7 5

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ROWS 45 42 4l 40 38 36 34 32 3I 30 29 28 26 25 22 23 2I IS I6 I4 I2 I I IO 8

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=:l-MANV/AY NOZZLE

~ - April 80 31 4/25/80 AEC

Attachment B

Evaluation of Results The results of the steam generator inspection have been reviewed to determine whether there are any unreviewed safety questions or whether a change in the Technical Specifications is required.

The conclusion has been reached that there are no unreviewed safety questions and that no change in Technical Specifications is required.

The current safety analysis assumes that 10% of the steam generator tubes are plugged.

Current plugged levels are well below 10%,

3.74% in the A and 3.44% in the B.

Therefore, the current analysis remains valid.

The current Technical Specification limit is O.l gpm in either steam generator when averaged over 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.

This limit was pro-posed on April 25, 1975 and was reviewed and approved by the NRC in license amendment no.

7 dated May 14, 1975.

This limit was established to ensure tube integrity following design basis events under the condition of tube cracking superimposed upon thinning of the tube to 60% of the wall remaining.

Tests and analyses performed and approved in 1975 demonstrated that if leakage was limited to 0.1 gpm, then the maximum possible crack size was limited.

Even assuming that the maximum length crack occurred on a previously thinned area when 50% tube wall remained, tubes did not fail during design basis transients.

A 40% plugging limit was, therefore, established to provide a level of conservatism.

Whereas the Technical Specification were established based on defects occurring above the tube sheet, crevice cracks seen this outage and in the previous two outages are below the surface of the lt tube sheet.

The tube in the vicinity of the crevice crack is pro-vided support by the tube sheet and the previous safety analysis of tube integrity may be conservatively applied.

Tube clearances within the tube sheet may vary from manufacturing tolerances from

.016 inches to.022 inches on the diameter.

These clearances are further reduced in operation by the deposits and corrosion'roducts in the crevices.

Therefore, the tubes in the crevice area are tightly confined within, the tube sheet, which provides reinforce-ment to the tube wall material in the area of the crevices where the intergranular corrosion attack has been found.

This would reduce tube distress under abnormal loadings prohibiting significant cracking or rupture.

Further, thinning in the crevice region has not been observed, thus providing significant additional margin.

Based on these considerations, there is no unreviewed safety question and no change in the Technical Specifications is required.

Plant operation may, therefore, resume.