L-77-393, Letter Transmitting Information Regarding Results of Unit 3 Steam Generator Inspections Conducted During the Current Refueling Outage

Letter Transmitting Information Regarding Results of Unit 3 Steam Generator Inspections Conducted During the Current Refueling Outage

ML18227B787
Person / Time
Site:	Turkey Point
Issue date:	12/29/1977
From:	Robert E. Uhrig Florida Power & Light Co
To:	Stello V Office of Nuclear Reactor Regulation
References
L-77-393
Download: ML18227B787 (39)

Text

DISTRIBUTION AFTER ISSUE CE OF OP STING LICENSE NRU<>oR~~ >I9S U.S. NUCI EAR REGULATORY COMMI OOCKE7 NUMBER Ig-r8) 5d - +5v FII E NUMBER gRC DISTRlBUTION FoR PART 50 OOCKFT MATFRlAL TO-'r. FROM:

Florida Power & Light Company OATE OF OOCUMENT 12/29/77 Victor Stello). Miami, Flori da DATE RECEIVEO Robert E+ Uhrig 1/3/78

~TTE R QNOTORIZEO. PROP INPUT FORM NUMBER OF COPIES RECEIVEO

~OR IQINAI ~NCLASSIFIEO SCOPY 3 pic Pcc3 OESCRIPTION EN CI.OSU R E Consists'of, the results of tPe Turkey Point Unit 3 steam generator inspections conducted during the current refueling outage+ ~ ~ ~

(2-P)

P~IT NAME: Turkey Point Unit 3

' JL 1/3/78 FOR ACTION/INFORMATION BRANCH CHIEF: 7 INTERNAL 0 IST Rl BUTION EG F MCGO EXTERNAL DISTRIBUTION CE ROL NUI'4BER PDR: p y +4 IC BASIC gCRS 1 CYS SENT CATE

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P. OX 013100, MIAMI, FL 33101 PEtWM'tto27 MP'3 FIVE FLORIDA POWER & LIGHT COMPANY December 29, l977 L-77-393 Office of Nuclear Reactor Regulation Attention: Mr. Victor Stello, Director Division of Operating Reactors U. S. Nuclear Regulatory Commission Washington, D.C. 20555

Dear Mr. Stello:

Re: Turkey Point Unit 3 Docket No. 50-250 Steam Generator Ins ections The results of Turkey Point Unit 3 steam generator during the current refueling outage are attached.

inspections'onducted The inspections showed no new phenomena and confirmed. that. the general pattern of denting in the Unit 3 steam generators is consistent with previous observations at Turkey Point Unit 4.

However, the rate and extent of denting is somewhat. less on Unit, 3. This was expected based on the Unit's good operating history.

The general criteria, applied for steam generator inspections and preventive plugging are the same as those previously applied to Turkey Point Unit 4. This program was demonstrated to provide reasonable assurance of steam generator tube 'integrity such that safe operation of the Unit during normal'ull pawer operation and during hypothetical accident conditions was assured for an ooerating period in excess of 6 effective full power months (EFPM). Applying this same program to Unit 3, which is affected less than Unit 4, produces additional conservatism in the re-sulting preventive plugging program.

In addition to the preventive plugging resulting from the. tube gauging program, we have elected to additionally plug any remain-ing unplugged tubes in the "hard spot"'regions adjacent to the tube lane out to Row 3. This requires plugging 37 additional tubes and provides additional assurance of minimizing tube leakage.

Regulatory Guide 1.83 inspections required plugging only 5 tubes.

Additionally, several tubes will be plugged to correct for some minor errant plugging detected via tube sheet photographs. This errant plugging consisted of correctly plugging one end of a tube and then misplugging on 'the other side of the channel head due to incorrect tube identification. However, no tube plugs were determined to be missing.

PEOPLE... SERVING PEOPLE

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W I

. Nr. Victor Stello, Di. tor Division of Operating Reactors

. Pa e Two Total S/G plugging at the conclusion of the current outage will be approximately 11.4%. This is conservatively bounded by the 1S% tube plugging ECCS analysis which has been previously sub-mitted.

Based on the inspection results, the implemented plugging pattern, and previous analyses submitted in conjunction with Turkey Point, Unit 4, we have concluded that Turkey Point. Uni< 3 can be re-turned to full power operation without adversely affecting public health and safety. Therefore, we request that Turkey Point Unit 3 be permitted to continue to operate within the constraints of the existing'acility Operating License.'ery truly yours, Robert, E. Uhrig Vice President RZU/MAS/RJA/lah Attachment, cc: Nr. James P. O'Reilly, Region Robert Lowenstein, Esquire II

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'UBE PLUGGING PATTERN r R TURKEY POINT NO. 3

1. INSPECTION 'PROGRAM The tube gauging program is based on expected regions of high tube deforma-tion. These regions are determined by the finite element analysis which,'hen.

combined with tube strain tests, yields tube hoop strains.=versus tube location and extent of plate deformation. The plate deformation, is indicated by the amount of flow slot closure. The validity of the approach has been confirmed by the results of inspections auld reinspections,at other sites (Surry,l, Surry 2, and Turkey Point 4). Figure 1 illustrates the flow slot closure history at Turkey Point 3. This figure displays the average flow

,slot closures at this outage for flow slots 1 and 2 and previous outage data for. support plates 1 and 6 of steam generators A thru C. Support plate No. 2 in steam generator B,is the most severely deformed. Figure 2 illustrates the sequence of computer runs to full flow slot closure and for 12 months beyond. Figure 3a to 3e present the tube hoop strain contours for these computer runs. Figures 3c and 3d bound the current conditions of tube support plate No. 2 in steam generator B. These strain maps are usedf to develop the tubelane inspection program. llhile it has been established .that the 15%

strain contour is the most appropriate inspection boundary, the 12.5X strain contour'was used as a boundary. for this outage since this was the first time that Turkey Point 3 was inspected under this program. However, the results again indicate the adequacy of a 155 contour as a boundary.

The identification of the inspection region by the 12.5X contour is illus-trated in Figure 4. Additional inspection programs are defined for the wedge and patch plate regions. These programs are based on previous leaker history at the Turkey Point and Surry sites, as well as previous gauging results at the Surry and Turkey Point 4 sites, as deemed appropriate.

During this inspection an additional probe size (0.580") was utilized in order to collect more definitive gauging data. It is anticipated that in future reinspections of this and other units that this probe size wi'1 1 be incorporated into the plugging criteria.

The entire inspection program is outlined in Figure 5. An additional conser-vative inspection criterion has been established. This criterion is that

.the inspection will go two rows beyond any tube that restricts a 0.650 inch probe in the tubelane and wedge regions, and two tubes on either side of a tube that restricts a 0.650 inch probe in the patch plate region.

The strain maps shown in Figures 3b and 3c indicate regions near the tube-lane of strain in excess of 15K on the coldleg side. This is indicative of the behavior in steam generator B only since no visible plate in steam generators A and C exhibit average flow slot closures in excess, of 2.25 inches.

At this level of plate expansion there are no significant regions of high strain. Due to the current awareness of the potential for future tube deforma-

'I tion on the coldleg side, a limited inspection in steam generator B was performed during this outage in'conjunction with the U-bend inspection program

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conducted on the coldleg of steam generator B. At future inspections coldleg gauging will be defined for each steam generator as is appropriate.

2. EVALUATION OF INSPECTION RESULTS The results of the inspection. program, which is described in Section 1 and outlined in Figure 5, are presented in Figures 6 through 8 for steam generators A, B and C respectively. These results support the adequacy of the inspec-tion program described above and the plugging criteria which will be presented in the next section. Specifically: =-

(a) Only one tube leak occurred over the past 9 months of operation. That leak was close to the tubelane, remained at a relatively low rate

(<.1 gpm) for over three months, and did not cause an unscheduled shut-'own.

(b) All tubes in the tubelane region that restrict the 0.650 inch probe, or any smaller size probe, lie well within the 12.5X strain boundary. In addition, all of these tubes lie within the 15% strain boundary.

(c) In the tubelane region there are 27 tubes in steam generator B that restrict the 0.540 inch probe. In steam generator C, which appears to be more than 6 months behind steam generator B in terms of degrada-tion (as measured by extent of flow slot closure), only 13 tubes restrict the 0.540 probe in the tubelane region. In steam generator A, which follows B by approximately 12 months, only ll tubes restrict the 0.540 probe in the tubelane region. All 27 of the 0.540's in steam generator B, lie below row 7 with only 3 of these tubes in row 6. All 13 of the 0.540's in steam generator C lie below row 5, with only 1 in row 4. All 11 of the 0.540's in steam generator A lie below row 5, with only 1 in row 4. Two conclusions--can be formed from these results .

First, quite obviously a significant number of tubes that restrict the 0.540 inch probe have remained in service for several months. Second, the outward movement of tubes that restrict the 0.540 inch probe is less than 2 rows in 6 months.

(d) In steam generators A, B, and C the restricted tubes are packed closely together. This is particularly true of the tubes that restrict the 0.540 and 0.580 probes. Thus, the activity is moving in a stable manner, adjacent to previous activity.

(e) Activity was noted in wedge and patchplate areas of all steam'enerators and this activity appears consistent with previous experience at other units. Based on the behavior of these areas at other,,sites,.the current plugging criteria should stabilize these regions.

(f) On the coldleg side of steam generator B all indicated tube restrictions were bounded by hotleg gauging results and plugging patterns and were consistent with the strain contour maps, which further indicate that this coldleg activity will grow at a very slow rate. It may be necessary at future inspections to probe tubes on the coldleg side of the bundle to the extent dictated by the tube strain contours.

Implementation of the current plugging criteria, following this very extensive gauging program, supports in excess of six months of continued operation.

3. PLUGGING CRITERIA From Figure 1, the maximum rate of closure at Turkey Point 3 is less than,.12 in/mo and. occurs at the 2nd plate in steam generator B which is at full

closure at 27.2 EFPH's (AVT). This rate is considerably higher than that for all other visible plates in the three steam generators. Note again that, as with .Turkey Point 4, there appears to be an abrupt change in the rate of closure of several of the plates as compared to previous inspections. This

..is primarily due to cracking at the edge of the flow slots and is not a real indication of a change in the rate of expansion. Therefore, a rate taken over the whole 2? months period is most appropriate. The closure of the 2nd plate in steam genera'tor B is closest to the closure represented by-runs 4-3 and 4-4 (See Figure 2). Figures 3c and 3d are the plots of tube strain contours for these runs. Figure 3e represents the strain contour at 12 months beyond full closure or approximately 12 EFPH's from the current time. 'Location of previous leakers and previous gauging programs have indicated that tubes which cannot pass the 0.540 inch probe should be used as the basis for the plugging criteria.

4 Correlation of the leaker history, gauging results and computer produced strain contours have confirmed the 1?.5$ contour as the one which best repre-sents the outward movement of the highly deformed tubes. However, since this is the first implementation of this program at Turkey Point 3, the 15%

=

contour will be used. This is consistent with the highly conservative inspec-tion boundary of the 12.55 strain contour. The growth of this contour (based on computer runs 4-3, 4-4, and 4-5) is displayed in Figure 9. From this Figure, the rate of growth is very conservatively set at 1/3 row per month over most of the tubelane, and 2/3 row per month at the outside columns over the next period of operation. Thus, for a 6 month operating period 2 rows should be plugged over most of the tubelane and 4 rows at the outside columns .

'Again, it should be pointed out that there have been numerous cases of tubes restricting the 0.540 inch probe for some time and not yet leaking. This is an additional conservatism.

The criterion established for plugging tubes in the region of the patchplate differs from that used for other regions of the bundle. Figure 10 maps all tubes in th'e vicinity of the patchplate which have leaked. They have at the perimeter of the plate or near to the patchplate boundary, all'ccurred where plug welds connect the patchplate to the main body of the bundle. All

data still indicates that the phenomenon at the patch plate is local-in nature and should not be attributed to the general strained state of the plate, nor can the phenomenon be represented by the finite element model. While the hoop strains in this region are not high enough in themselves to cause severe tube deformation, they are high enough to act as catalysts for the local phenomenon

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which occurs at the patch plate. Due to these factors, the region of the. patch plate requires its own inspection program (Figure 5) and a corresponding plugging criteria. Because of the fact. that leakers in this region have not always restricted 0.540 inch probes, leakers and tubes that restrict the 0.540 inch probe will be treated alike, and the surrounding tubes about both will be plugged. In addition, tubes that restrict the 0.610 inch probe will be plugged, and as a final'onservatism tubes on either side of the. patch plate boundary, (plate perimeter on one side and plug welds on the other three sides) that restrict the 0.650 inch probe will be plugged.

Finally, due to the local plate cracking that is believed to occur at the periphery and near wedge locations, tube leaks can occur here. at lower levels

.of tube restriction than in the tubelane. Thus, the wedge at.eas require their own inspection program and plugging criteria. The plugging criteria at wedge locations calls for treating leakers and tubes that restrict the 0.540 inch probe in a similar manner. In addition, tubes that restrict the 0.610 inch probe and peripheral tubes that restrict the 0.650 inch probe will be plugged.

The plugging criteria which supports at least six months of operation are:

(a) All tubes which do not pass the 0.540 inch probe will be plugged.

(b) Additionally, for in excess of six (6) months operation, two (2) tubes beyond (i.e., higher row numbers) any tube in columns 14 to 80 which did not pass the 0.540 inch probe will be plugged; for such tubes in columns 1 to 13 and Sl to 94 near the tube lane, a'aximum of four tubes and a minimum of two tubes (at the edges of the flow slot) beyond any tube which would not pass a 0.540 inch probe will be plugged.

(c) All tubes which do not pass the 0.610 inch probe will be plugged.

(d) The tubes in any column for which plugging under criteria (a), (b),

or (c) above is implemented will also be plugged in the lower row numbered-tubes back.to the tubelane if not already plugged.

(e) As a conservative measure, tubes completely surrounding any known leaky tubes including the diagonally next tube - will be plugged, if not already covered by the foregoing criteria.

(f) In any given column which is surrounded by columns containing tubes with significant tube r'estriction or prior plugging, (thereby creating a

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"plugging valley" in the pattern) engineering judgment will be used to fill the bottom of the valley. In the periphera7 tubelane areas near the three and nine o'lock wedges, tubes surrounded by previously plugged tubes or tubes exhibiting high deformation activity will be plugged based on engineering judgment.

(g) Additional preventive plugging will be implemented at the wedge locations.

This plugging will include all tubes that:

(1) restrict the 0.540 inch probe.

(2) restrict, the 0.610 inch probe.

(3) restrict the 0.650 inch probes at the periphery.

(4) surround leakers and tubes that restrict the 0.540 inch probe including the diagonally next tube.

(h) Additional preventive plugging will be implemented in the patch plate region. This plugging will include all tubes that:

(1) restrict the 0.540 inch probe.

(2) restrict the 0.610 inch probe.

(3) surround leakers and tubes that restrict the 0.540 inch probe including the diagonally next tube.

(4) Lie on either sides of the patch plate boundary (plate perimeter on one side and plug welds on the other three) and restrict the 0.650 inch probe.

'4. ACTUAL PLUGGING PATTERN ll, 12, and 13 indicate the plugging patterns for Turkey Point Unit

'igures 3

steam generators resulting from the application of the plugging criteria stated above.

FULL CLOSURE 2.5 COTE: B-2 IS THE B-2 SECOND SUPPORT PLATE XN S/C a.

2.0 1.5 A-1 1.0

.5 B-6 C-6 A-6 10 20 25 30 EFPM/AVT FL ure 1

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3.0 5 mo. beyond closure 4 4

~L g~oams 12 mo. beyond CASE AV0. EXP.

4-3 closure .

4 .018 in/Ln 4-2 .035 in/in 2.0

. 4-3 .043 in/in 4-2 4-4 .057 in 4-5 .071 in/in

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.05500 Strains:

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. i0500 MAX . 1i2588 Represents location of the tubes which leaked at the indicated strain location n

3216 Figure 3g Tube Hoop Strain At .9" Closure

MIN .032056 1 .00000 3 .07000 Tube Hoop Strains: 5 . iOOGG 7 . 13000.

.oca S . i6000

.029 in/in Expansion ii i9000 MAX ..205%82 o Represents location of the tubes which leaked at the indicated strain conditions

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Figure 3b Tube Hoop Strain at 1.9" Closure.

MIN .032137 1 .00500 3 .07500

~5 . 10500 7 . 13500 Tube Hoop Strain: 9 . 1S500

.050 11  : 1S500

.036 in/in Expansion 13 .22500 15 ;25500 1,7 ,28500 1S , 31500 MAX :327773 32 i%

Figure 3c Tube goop Strain At 2.5" Closure

-MIN . 032260 i . 00000 3 .06000

. f2000 7 . f6000 Tube Hoop S train: 9 . PQOQO

.067 in/in Expansion i1 . 2%00G

,048 i3 . c 6000 i5 ..32000 f7 .36000 MAX;398688 I

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)i Figure 3d Tube Hoop Strain 5 . Months Beyond Closure

MIN . 032329 i .'.05000

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.059 in/in Expansion .

Tube Hoop Strain: 7 S

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,I jQ Figure 3e Tube Hoop Strain At12 Months Beyond Closure

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TURKEY APPOINT 3A.STEAN GENERATOR GAUGING RESULTS o ~ .580" Probe

• .610" Probe

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. MANWAY , FIGURE 7 TURKEY POINT 3B STEAN GENERATOR GAUGING RESULTS NOZZLE x ~

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,580" Probe

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• = .610" Probe rl~ .650" Probe

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IVlANWAY IFIGURE 8 TURKEY POItlT 3C STEAM GEt(ERATOR GAUGIt'G RESULTS NOZZLE 4 =

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• = .610" Probe 0 = .650" Probe

= 2/3 row/mo. (maximum) 1/3 row/mo.

l 12 NONTHS BEYOND FULL i Note that only'this one CLOSURE 1 area of the plate (near 5,0 MONTHS* BEYOND I

the 3 snd 9 o'lock wedges)

FULL CLOSURE I

be examined sepa- 'ust I rately with regard to 2.0 CONTI(S* PRIOR TO growth of strain contours, In all other regions, PULL CLOSURE

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I/3 row/mo. is a conser-vative growth rate.

Si0 .MONTHS* BEYOND)

PULL CLOSURE 12 MON'fllS BEYOND FULL CI OSURR Based on maximum expansion rate considered in analysis.

Pl.pure 9 "Grovth" of 15 Hoop Strain Contour

49 .Tubes Which Have Leake'6 Plug fields at Patch Plate Figure 10 Peripheral Leaks at Turkey Point Site

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