ML18227D390

Letter Attached Results of the Steam Generator Inspections Conducted During August, 1978

ML18227D390
Person / Time
Site:	Turkey Point
Issue date:	09/06/1978
From:	Robert E. Uhrig Florida Power & Light Co
To:	Stello V Office of Nuclear Reactor Regulation
References
Download: ML18227D390 (30)

Text

REGULATORY INFORMATION DISTRIBUTION SYSTEM (HIDS >

DISTRIBUTION FOR INCOMING MATERIAI 50-251 REC:

STEI LO V NHC ORG:

UHRIG H E FL PWR

8. LIGHT DOCDATE: 09/06/78 DATE RCVD: 09/i i/78 i

DOCTYPE:

LETTER NOTARIZED:

NG

SUBJECT:

FORWARDING RESULTS OF SUBJECT FACILITY"S STEAM CONDUCTED DURING AUGUSTA i978.

COPIES RECEIVED LTR 3 ENCL 40 GENERATOR IN PECTIONS Pl ANT NAME: TURKEY PT 44 REVIEWER INITIAL:

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><<<<<<Ski>>4-Tl-IF END CONTROL NBR: 7+480203 I <<<<<<<<<<%<<<<%4.>>>><<<<<<->>>><<<<<<<<<<%<<<<<<<<<<<<<<<<<<<<<<% Op I y tl I'l h FLORIDA POWER 8I LIGHT COMPANY September 6, 1978 L-78-'291 Office of Nuclear Reactor Regulation Attention: Mr. Victor Stello, Director Division of Operating Re 4@gpgggggg U. S. Nuclear Regulatory Commission ~~<<~ UHf' tt-EN t.'=i'<x Washington, D. C. 20555 ~> tlLE(Q J C XI

Dear Mr. Stello:

Re:

Turkey Point Unit 4 Docket No. 50-251 Steam Generator Ins ections The results of the Turkey Point Unit 4 steam generator inspections conducted during August,

1978, are attached.

The inspections verified that the progression of the denting' pattern is well within predictable limits.

The total plugging resulting from this inspection is 176 tubes.

This total represents 155 tubes plugged due to denting considerations, 20 tubes plugged due to wall

thinning, and 1 tube which was erroneously plugged.

The plugging criteria applied provide reasonable assurance of steam generator tube integrity and enable safe operation of Turkey Point Unit 4 during normal full power operation and during hypothetical accident conditions for an operating period in excess of 6 equivalent full power operating months.

,The initial evaluation of the wall thinning data indicates that thinning rates have not increased.

However, for additional assurance, a more detailed evaluation is being performed.

Total steam generator tube plugging at the conclusion of the current outage will be approximately 18.7%.

This level of plugging is conservatively bounded by previously submitted ECCS analyses.

Based on the inspection results, the implemented plugging

pattern, operating history, and previously submitted

analyses, this report concludes that Turkey Point Unit 4 can 73+ggp203 PEOPLE... SERVING PEOPLE

0 Mr. Victor Stello, Director U. S. Nuclear Regulatory Commission September 6, l978 Pa e Two 0

be returned to full power operation for at least 6

equivalent operating months without adversely affecting public health and safety.

Very truly yours, E~r Robert E. Uhrig Vice President REU:RJA:dt Attachment cc:

Mr. Zames O'Reilly, Region II Robert Lowenstein, Esquire

l

TUBE PLUGGING PATTERN FOR TURKEY POINT UNIT 4 l.

INSPECTION PROGRAM The tube gauging program is based on expected regions of high tube deformation.

These regions are indicated by the finite element analysis, which, when combined with tube strain tests, yields tube hoop strains versus tube location and extent of plate deformation.

Initially, the 12.5%

strain boundary was used in 'the gauging program when little plant specific data was available.

After two initial inspections and two reinspections of the Turkey Point

plants, we now have the benefit of plant specific information which indicates the conservatism of the 12.5%

boundary and the adequacy of the 15% boundary.

That is, the majority of the tubes inspected do not restrict the

.650 inch probe.

In addition, all tubes restricting the

.610 inch or.540 inch probe in the tubelane

.region have all fallen well within the inspection boundary.

This is significant since the'.610 inch and the

.540 inch restricted tubes form the basis for the plugging patterns in'he tubelane region.

Since full closure of some flow slots was observed in Turkey Point Unit 4 steam ge'nerators during the May-June, 1977 inspection, Turkey Point Unit 4 is regarded as beyond full closure by approximately ll EFPM's.

The tube hoop strain contours calculated for 12 EFPM beyond full closure (Figure

1) were utilized to determine the 15% boundary for this inspection.

Figure 2 for 18 EFPM beyond full closure bounds the approximate condition expected after six months of additional operation.

The identification of the inspection region by the 15%

contour is illustrated in Figure 3.

Additional inspection programs are defined for the wedge and patchplate 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 sites, as deemed appropriate.

The strain map shown in Figure 1 indicates regions near the tubelane of strain in excess of 15% on the cold leg side.

Due to the current awareness of the potential for tube deformation on the cold leg side, an inspection of the cold legs of all three steam generators was performed during this outage.

The entire inspection program is outlined in Figure 4.

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The following additional conservatisms were utilized in determining the Turkey Point, Unit 4 inspection boundary:

A.

In the flow slot area, it is estimated that the 15% strain boundary at 12 EFPM beyond full closure extends to approximately the 8th row.

The inspection boundary for this inspection extended to the 12th row in order to be consistent with previous inspection plans.

B.

When a restricted tube was found close to the inspection

boundary, the inspection was expanded in that area.

2.

EVALUATION OF INSPECTION RESULTS The results of the inspection

program, which is described in Section 1 and outlined in Figure 4, are presented in Figures 5 thru 7 for Steam Generators A, B, and C, respectively.

These results support the adequacy of the inspection program described above and the plugging criteria which will be presented in the next section.

Specifically:

A.

No tube leaks occurred over the last six months of operation.

B.

Tubes in the tubelane region that restrict the 0.650 inch probe lie within the 15% strain boundary.

In

addition, 0.540 inch restricted tubes lie within the 17.5%

strain boundary.

C.

In the tubelane

region, there were only two tubes in Steam Generator A that restricted the 0.540 inch probe.

D.

In Steam Generators A, B, and C, restricted tubes in the tubelane region developed adjacent to previous activity.

This is particularly true of the tubes that restrict the 0.540 inch and 0.610 inch probe.

Thus, the activity appears to be moving in a stable manner.

E.

Activity was noted in wedge areas of all steam generators including the cold leg wedge areas inspected.

Since this is the first time these affected cold leg wedge areas had been inspected, it appears that this activity has developed over the long term versus over the last six months.

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.

~ II

F.

Indicated tube restrictions on the cold leg side in the tubelane region fell well within appropriate strain contour boundaries and were adjacent to previous activity.

This indicates that cold leg activity in the tubelane region continues to grow at a slower rate as compared to the hot leg activity.

Implementation of the current plugging criteria, following this very extensive gauging

program, supports greater than six months of continued operation.

3.

PLUGGING CRITERIA The progression of strain contours over the intended operating period is utilized as the basis for preventive plugging of tubes in the tubelane region which are located in rows beyond 0.540 inch restricted tubes.

In earlier inspections, the closeness of the strain contour lines prevented identification of the appropriate contour which most reasonably indicated the extent and progression of tubes with greatest deformation.

Initially, the 15% strain contour was chosen when limited plant specific data was available and the strain contour lines indicated by finite element analysis fell close together on the plots.

A review of the relationship between the most restricted tubes at Turkey Point Unit 4 at this time and the finite element analysis strain contours at 12 EFPM beyond full closure indicates that the 17.5% strain contour more realistically estimates the boundary of these restricted tubes.

Also, the movement of the 17.5% strain contour over the next period of operation in the central tubelane region should be less than two rows in six months.

The growth of this contour is displayed in Figure 8.

From this Figure, the rate of growth is 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 six-month operating period, two rows should be plugged over most of the tubelane and four 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 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.

All leaks in the patchplate region have occurred at the perimeter of the plate or near to the patchplate

boundary, where plug welds connect the patchplate to the main, body of the bundle.

All observed data still

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indicate that the phenomenon at the patchplate 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 do not appear high enough in themselves to cause severe tube deformation, they apparently are high enough to act as catalysts for the local phenomenon which occurs at the patchplate.

Due to these factors, the region of the patchplate should have its own inspection program (Figure 4) 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 should be treated alike, and the surrounding tubes about both should be plugged.

In addition, tubes that restrict the 0.610 inch probe should be plugged, and as a

final conservatism, tubes on either side of the patchplate boundary (plate perimeter on one Side and plug welds on the other three sides) that restrict the 0.650 inch probe should be plugged.

Finally, due to the local plate cracking that is believed to occur at the periphery and near wedge locations, tube leaks may occur here at lower levels of tube restriction than in the tubelane.

Thus, the wedge areas should have their own inspection program and plugging criteria.

The plugging criteria at hot leg 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 should be plugged.

Cold leg plugging will be based on the degree of activity noted and rates of progression observed from gauging.

The plugging criteria which support 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 months operation, two tubes beyond (i.e., higher row numbers) any tube in columns 15-79 which does not pass the 0.540 inch probe will be plugged in the tubelane region; for such tubes in column 1-14 and 80-94, four tubes beyond 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),'r (c) above, is implemented in the tubelane region will also be plugged in the lower row numbered tubes back to the tubelane if not already plugged.

0

E.

As a conservative

measure, tubes completely surrounding any known leaking tubes including the diagonally next tube will be plugged if not already covered by the foreg'oing criteria.

F.

In any given column which is surrounded by columns containing tubes with significant tube restriction or prior

plugging, (thereby creating a "plugging valley" in the pattern) engineering judgement will be used to fill the bottom of the valley.

In the peripheral 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 judgement.

G.

Additional preventive plugging will be implemented at the hot leg wedge locations.

This plugging will include all tubes that:

l.

2.

3.

4 ~

restrict the 0.540 inch probe restrict the 0.610 inch probe restrict the 0.650 inch probe at the periphery surround leakers and tubes that restrict the 0.540 inch probe, including the diagonally next tube H.

Application of the criteria specified in G, above, will be made on the basis of engineering judgement for cold leg wedge locations.

I.

Additional preventive plugging will be implemented in the patchplate region.

This plugging will include all tubes that:

l.

2.

3.

4 ~

restrict the 0.540 inch probe restrict the 0.6l0 inch probe surround leakers and tubes that restrict the 0.540 inch probe including the diagonally next tube lie on either sides of the patchplate boundary (plate perimeter on one side and plug welds on the other three) and restrict the 0.650 inch probe 4.

ACTUAL PLUGGING PATTERN Figures 9, 10, and ll indicate the plugging patterns for Turkey Point Unit 4 steam generators resulting from the application of the plugging criteria stated above.

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