Text

Letter Enclosed Requested Information on Steam Generator Integrity & Presenting Analysis Results to Question No. 5 on Significant Tube Denting
	ML19098B401
Person / Time
Site:	Surry
Issue date:	01/14/1977
From:	Stallings C; Virginia Electric & Power Co (VEPCO)
To:	Reid R, Rusche B; Office of Nuclear Reactor Regulation
References
	Download: ML19098B401 (22)
	v • d • e

,*

e VIRGINIA. ELECTRIC.A.ND POWER COMP.A.NY RICHMOND, VIRGINIA 23261 Mr. Benard C. Rusche Director of Nuclear Reactor Regulation U. s. Nuclear Regulatory Commission Washington, D. t.

20555 ATTENTION:

Mr. Robert W. Reid, Chief Operating Reactors Branch 4

Dear Mr. Rusche:

.. :*~.....

Serial No.

2600/092276 PO&M/ ALH :j c Docket Nos.

50-280 50-281 License Nos. DPR-32 DPR-37 The purpose of this letter is to answer questions raised by your staff as a result of our submittal dated January 3, 1977 on the subject of steam generator integrity at Surry.

The requested information is enclosed in the attachment to this letter.

The analysis results presented in our response to question number 5 show that areas of significant tube denting (

11hard spots 11

) are restricted to regions near the tube lane flow slots and the support plate wedges at the perifery.

Expansion of the support plate due to corrosion product buildup with time does not result in the creation of additional 11 hard spots, 11 but causes existing 11hard spots 11 to become more strained (i.e.

11 harder 11 ).

Further, the insertion of a flow slot blocking device, which restricts the further closure of the tube lane flow slots, shifts the area of maximum strain to the periferal wedge area, but does not create new hard spots or cause the boundaries of existing ones to expand.

Further, by stopping the closure of the tube lane flow slots, U-bend cracking is prevented. This is discussed thoroughly in Attachment l to our January 3, 1977 submittal.

The analyses also show that the support plate growth rate does not increase with expansion.

We would therefore expect the corresponding strain rates to perform similarly with time.

This is significant because research to date indicates that strain rate is an importarit factor in causing cracking in Ni-Cr-Fe alloy 600 steam generator tubes.

r,.

vrnornIA ELECTRIC.AND PowER0--GoMPANY *TO*

Mr. Benard* C. Rusche The information gathered to date shows that the preventive tube plugging program and the installation of flow slot blocking devices as presented in our January 3, 1977-submittal wi 11 pr~vent pri'mary to secondary leaks resulti_ng from 11U-bend 11 failures and essentially eliminate 11dented region 11 tube leaks *. The analyses show that this conclusion is valid for at least two months of full power operation.

We are continuing to develop a comprehens,ive program to validate our analysis results. The details of this program will be finalized within two calendar months.

2 Werequest that Surry Unit No. l be permitted to operate for two effective full.power months (EFPM).

Prior to the end of this period of operation, we intend to conduct and evaluate additional analyses to justify continued operation.

The results of our findings will be submitted to your

--staff. If these analyses are inconclusive or do not meet with your approval, we intend to shut-down Surry Unit No. l at the end of the two EFPM. period and re-evaluate the condition of the steam generators prior to further operation.

We believe that this approach is conservative and justified.by

the information presented in our January 3, 1977 submittal and in the attachment to this letter.

Attachment Very truly yours,*

tJ.)I)!;_ ~aa~y C... M. Stallings Vice President-Power Supply and Productien Operations

1.

ATTACHMENT e

e The equivalent strains have been calculated *for every row 1 tube removed from Surry #1, Surry #2, and Turkey Point #4~

This infonnation is correlated with tube crack locations (denoted by the letter "C"), measured ovalities and

§_ffective Full *g_ower N_onth in Figures 1 to 1-3.

'./)'\\

"'.i.

':\\

i,*.

Figure 1-1.

Row 1 Tubes Removed At Surry #1 COLUMN EQUIVALE,!'JT S~IN MEAS~~D OVALITY

.;3

.136 6.6 4

C

.138 15.5 5

C

.143 24.2 6

C

.147 29.3 e

7 C

.147 41.3 8

C

.150 31.4 9

C

.152 15.9 10 C

.. 149 31.9 11 C

Q 146 28.3 12 C

.. 142 25.3 13 C

.136 16.2 14

~~ ;

.134 7.9 15

.132 6.4 C DENOTES CRACKED TUBE

(%).

ATTACHMENT EFPM Removal:

15.4 on AVT

ATTACHMENT Figure 1.. 2.

Row 1 Removed At Surry #2 COLUMN EQUIVAL~NT STRAIN MEASURED OVALITY_(%)

1

.133 0

EFPM 2

.133 0

e 3

.135

0.7 Removal

4 *C

.136 2.4 15.2 on 5 C

.140 9.0 AVT 6

C

.. 142 12.5 7

C 8

C

.143

11. 7*

9 C

.143 13.3 C DENOTES CRACKED TUBE

ATTACHMENT Figure 1.. 3.

Row 1 Tubes Removed At Turkey Point # 'I COLUMN EQUIVbLENT STRAI_N MEASURED, OVALITY (%)

91 90 EFPM e

89

.136 10.0 88

.137 16.0 Removal:

87

.138 17.9 18 on 86 C

.139 18.0 AVT 85

.140 16.0 84

.139 14.3 83 C

.138

12. 9 82 C

.138 12.7 81

.136

10. 9 80

.134 Q9

( \\ ::I 79

/

0 DENOTES CRACKED: TUBE

ATTACHMENT 2.a The manufactured strain and the worst me'as.ured "hourglassing" stra;in for the tube in row 1, column 1-8 are presented in the table below together with the, total strains and the equivalent strains.

~

~

urnn 1

Total 2

Total

3.

Total

4.

Total

5.

Total

6.

Total

7.

Total

8.

Total E axial

.. 177

.177

.006

.183

.. 012

.189

.017

.194

.022

.199

.024

.201

.026

.. 203 TABLE 2.a E hoop

.004

.001

.004

.007

.011

.013

.017

.016

.020

.026

.030

.017

.021

~"Strain due to hourglassing *

- No Leg Displacement E radial

-.040

-.001

-.041

-.004

-.044

-.007

-.047

-.009

-.049

-.010

-.050

'-~010

-.050 E equ

.133

',,.133

.133

.136

.138

.143

.147

.150

e ATTACHMENT

2.,b The manufactured strain and the "hourglassing" strain for the row 1 tubes.,

if they are deformed to full closure, are presented in the table below for column 1-8 together with the total strains and the equivalent strains.

e:

. 1 axia TABLE 2.b e:

h oop

~

.177

.004 mn 1

Total 2

Total 3

Total 4

Total 5

Total 6

Total 7

Total 8

Total

.177

.004

.177

.004

.008

.003

.185

.007

.016

.011

.193

015

.023

.020

.200

.024

.032

.025

.209

.029

.036

.038

.213

.042

.038

.031

.215

.035

Strain duet~ "hourglassing11

.No Leg Displacement e:

e:

d" 1 ra ia equ

-.040*

.133

-.040

.133

-.040

.133

-.001

-.041

.137

-.006

-.046

.143

-.009

-.049

.145

-.012

-.052

.153.

-.014

-.054

.155

-.014

-~054

.157

e ATTACHMENT 3e At the resumption of power operation of Surry Unit 2 on December 20, 1976, primary to secondary leakage was detected in A Steam Generator.

The plant was taken off-line on December 22, 1976 for leakage location and repair.

Two tubes were found to be leaking, R4C63 and Rl2C4, both below the 7th (uppermost) tube support platee These tubes were plugged and the Unit returned to power on December 26, 1976.

The two tubes in question are tabulated in Table l of Attachment 2 of the VEPCO submittal of January 3, 1977.

Both tubes-are located in "hard-s pot" regions of the tube support plate.

However, no data are available specifically for these tubes to permit calculation of the effective strain level that may have contributed to their*failure.

Currently, the only actual description available for a hard-spot.tube leak is that obtained frotn examination of tube R2-C42, removed from Surry Unit 1, steam generator C.

The findings by laboratory examination of this tube were d~scribed in a Westinghouse/VEPCO/NRC telephone conversation.

There is considerable uncertainty in these results because of the deformed condition of the tube, believed to be caused during tube extraction, and the large strains in the region of the tube close to the* mid--plane of the support plate.

This is the result of changes in shape of the tube cross section from circular to distorted (somewhat elliptical) within the support plate.

At the present time no measurements are available for tubes surrounding the wedges and flow slot "hard spots" which would appropriately define the strain levels in tubes.

Such strains could only be determined from actual diametral measurements aiong a tube.

However, crush tests, finite element results, and field data on dents all suggest substantially lower denting and subsequent ovalization for these tubes.

Tubes in the hard spot regions have denting significantly

... *-* --.~,--- -~-- _,.., ____,,.. -,. ________ ---*~---,.,-----~-..... ".~-........... --~~***

... -----* --~------------* ----~~~..... -.-***-****--*-*******-... **-*----*-.-*** *-**-.... -* **-*- ----- - -..

greater than tubes outside of these regions.

Using this rationale of the deformation patterns of the "boundary" tubes results in equivalent strains of less than.10 in/in.

4c

The two figures referenced exhibit flow slot closures of approximately.40 and c53 inchesQ Based on a closure rate of.15 inches/EFPM for S/G A, this gives an operating time equivalent of approximately 2.7 months for the.014 in/in expansion run, at which time the blocks were added to the model, and approximately 3.5 months for the.021 in/in expansion run.

Thus, the.021 in/in expansion run represents 0.8 months of operation after insertion of the blocks.

For S/G Band Ca more appropriate rate of closure is.07 inches/EFPM. Here, c014 in/in expansion corresponds to 5.7 months of operation and.021 in/in expansion run represents*approximately 2 months of additional operation.

5.

To date li has performed three finite element-analyses of the top tube support plate subjected to different rates of expansion, e.g.,.014,.021,.042/.030 in/in.

The strain intensity profile (Figure *5-1 to 5-3) for all three cases are quite similar, all indicating maximum strain rates in the "hard spot" regions.

There are no significant changes in the regions of high strain intensities in going from.014 in/in of expansion*to.042 in/in of expansion.

Note, that there are some changes in the.042/.030 in/in run due to the modeling changes that have been accomplished recently, (i.e_., considering different rates*for hot and cold legs of.042 and.030 in/in) but these do not affect results outsiqe of the "hard spot" regions.

The.042/.030 in/in run represents an average closure of 1.1 inches.

This is equivalent to 7.3 EFPM's at a closure rate of 0.15 in/EFPM.

Thus, to date, there has been every indication that the plate expansion continues in a predicable fashion and the pattern should not.

change from that exhibited for 15.4 EFPM's, the time at which the blocks were inserted.

Further, the profiles for.021 in/in expansion with blocks inserted

~

e Shaded area represents regions of strain intensity ~ 50 % of max.

.014 *in/in E:CPA.. 'l'SION LOAD erTACHMENT STRAI~- rnTE~SIT'.C El-E2 in/:.-:i.

1

.004 5

.* 020 9

.036 MAX *.0*1s-@

Average Flow Slot Closure=.40 in.

In Pla~e St~ai~ Intensities Free Flow ~indows Figure 5-1

~.

I I..

i.. I *

~--

\\

.}

e e ATTACHMENT Shaded area represents regions of strain intensity~ 50 % of max.

STRAIN INTENSITY El-~2 in/in

.021 in/in E..."\\PANSION LOAD In Plane Strain Intensities Free Flow Windows

FigU1:e 5-2

.L 5

"7,

9 t1 13 15 (i)-MP.:l

Shaded area represents regions of strain intensity 2: 50 % of max.

ATTACHMENT e

.042/.* 030 in/in Hot/Cold EXPANSION LOAD

... ~. *..

'Hot Cold Side

STRAIN*

51 SERIES T. S. PLATE 2ND GEN.

STRAIN INT Ei-E2 Figl)re 5-3

...... _ ----*-*---......... --,----* '....,...... --**---~--...... ------**** -

MIN. ooas.:;.a

1. 0 :GO::J 3

. 03GCO 5

. oscso 7

. 07GGO 9

. 0:3C!OO 11

. 11COO 13

. 13000 15

. 150GO Iv\\

17 *. 17COO

~-MAX. 1854-57 Average Flow Slot Closure= 1.1 in.

CASE C

"*.J'

-..:~;-:

~--,--.

f

~ *..-.. ~

.e e ATTACHMENT STRAIN ~TE~SITY El-E2 in/in 1

.004 D. ~ 2.4%

5

.020

9.

.036

~i}

~ 3.2%

MA."<

.021 in/in EXP *.\\..'{SION LOAD

.098 -G)

-~~--- --~.,.'.'"*--_.,. -***---~--- -**

... -~---*

In Plane Strain !ntensities,?lcw Wi~dows Blocked at.014 i~/in Load Condition Figure 5-4

£:.:..*

~:

"t:

- - -~.~-'t'-

o '?:.

m '?:.

e 2.4%

3.2%*

.021 in/in EX?A.,~SION LOAD FREE WI~mows In plane Strain Intensities Flow Windows Free Figure 5-5 e

ATTACHMENT STRAIN INTENSITY El-E2 in/in

.j 5

I

. n:=~r~*:1

. G: :~:;~;

..., -, """'r,

I :...,::....;:1*.-:

~

.. I I

e

/,

/

.59"

. -. ~ :.

.;.. ~-:.

014 in/in EXPAJ.~SION FREE WINDOWS e

AVERAGE FLOW SLOT CLOSURE=.40 in.

ATTACHMENT

. l I,.__ ____________________________ ___,

72",

I

\\

. ~ o 80 II

_\\_

.021 in/in EXPANSION LOAD FREE WINDOWS-AVERAGE FLOW SLOT CLOSURE =.53 in.

.78"

./.

' \\

\\

_J Figure 5-6

'.';I

. *I

/L~\\

I

.71'~/

I I r

.,. *: :">. --* : r.

...... : *-/*:~ -~..

/

/-

e

/

79" ATTACHMENT

-~~-

\\ -.......

' e

.021 in/in EXPA.i'ISION LOAD WINDOWS FROZEN AT.014 in/in EXPANSION LOAD

~.....

.79"

'----:---------------:__ _____ _j

/

1.02"~.

Hot t

. Cold i

. l I

\\

\\ /',

74"

.91" J ___ _

~-----'

* * ~"042/.030 in/in Hot/Col-d EXPANSION LOAD FREE WINDOWS AVERAGE FLOW SLOT CLOSURE = 1.1 in.

.75" Figure 5-7

',.,J:('

\\

. 92" -

\\\\

\\

I I

I L

/-~.80"

. *... :_/:

~.

e

(

.(

I fi...J Sh~ 11

....., * ~ t.., -

G

,...,.. *-J..... *.:**~~, -- -

-ATTACHMENT

!t hr;~... ".

\\;;i;~-

I

'Ji ATTACHMENT at.014 in/in (Figure 5-4) and without blocks inserted (Figure 5-5) indicate that the pattern changes by a negligible amount due to insertion of the flow slot blocks.-

The expansion of the plate at its periphery for the various analyses are shown in Figures 5-6 and 5.-7.

The results indicates two significant points:

1.

The expansion of the periphery is not linear with increased*expansion.

2.

The expansion of the plate at the perimeter is not worse with the blocks inserted than it is without the blocks inserted.

The relationship between periphal growth rate and uniform expansion load is shown on Figure 5-8.

All of this information serves to support the conclusion that plate growth during the continued operation of Surry# 1 with flow slot blocking devices is well defined and predictable.

Based on the above results, we judge that our current plugging pattern is appropriate during the next two months of operation.

We further expect that for the currently predicted expansion rate. of 0.15 inches/EF~M on flow slot closure, *the Surry #1 plates.will expand by less than.5 inches at the perimeter over the next 2 months.

Finally the responses to prev.ious questions, e,.

and those.included in this submittal about the shell, wrapper and wedges are applicable well beyoI).d the two months period.

This is true because they consider the maximum.load that "the plate, in any state, can apply to the wedges, wrapper and shell as discussed in the response to Question 4 of the January 3rd submittal.

ML19098B401

Text

Dear Mr. Rusche:

0.7 Removal

Navigation menu

Search