IR 05000263/1975001

IE Inquiry Rept 50-263/75-01Q (Cdr).Cracks Found in Feedwater Sparger in 751016-17 Insp at Monticello

ML20128C860
Person / Time
Site:	Monticello
Issue date:	10/21/1975
From:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
To:
Shared Package
ML20128C864	List: IR 05000263/1975001 IR 05000263/1975010
References
50-263-75-01Q-(, 50-263-75-1Q-(, NUDOCS 9212040552
Download: ML20128C860 (4)

Text

. .

,

= - - ~ - . _ - - - - - . - . . - _

-

.

4 ,, ,

' .

1 r I

i #

!

3 i 4 i i U. S. NUCLEAR REGULATORY C010i!SS10N'

!

j OFFICE OF INSPECTION AND ENFORCEMENT [

.

i l REGION III i 1 i

! .

j IE Inquiry Report No. 0$0-263/75-01Q (CDR) {

j Subjects Northern States Power Company I

i Minneapolis, Minnesota k T

t

_

i j License No. DPR-22 - Monticello Nuclear Plant ,

!

} Rework and Repairs - Feedwater Nozzles and Sparger Units Prepared bys . }ll . . L f ~- _ 0 Y $ / ll'{b .

]

' (Date)

1 Date and Manner NRC was Informed: *

/

+

1-

On September 25, 1974,. Region _III was notiffed, by-telephone, that cracks had been found in the feedwater sparger. On October 14, 1975, the region #

was informed,_by telephone, that cracks had-been.found in the feedwater 1 nozzles. An inspection was conducted at Monticello by C. H. Erb on ,

i October 16-17, 197 .

J u

! Description of Particular Event or Circumstance:

Approximately 200 crack indications have been'found on the inside of the-

vessel where the four horizontal ten-inch feedwater nozzles merge into the vertical wall of the reactor vessel. The indications were generally

,

i j concentrated in the upper and lower quadrants as_shown on the attached

drawing (figure 1).- The locations of the cracks as marked by crayon _for grinding are shown on the photograph of the 600 nozzle (figure 2)'. The

vertical axis is represented by the 0-1800'line.- All:four nozzles had

! some indications,: but the nozzle at 600 appeared to show more indications.

,

The. indications were parallel or nearly parallel to the axis of_the pipe

+

as shown on the photograph with penetrant applied, of the 600 nozzle at

330 orientation (figure.3).

! Action by the Licenseet

"

l This inquiry report contains information on the progress. to date, of the

,

'

grinding program on the nozzles' and the .atatus .of fabrication on the

'

sparger units. The grinding program will probably be complete by '

October- 22, 1975

e

.

.t l

[$8oEl

'

<

_ _ _ . . - _ _ _ _ _ _ _ _ .

.., .

-

L1 1

'

. ,

l 1 llistory

Other plants, including Dresden, Quad-cities and Hillstone 1, have experienced cracks in their feedwater sparger assemblies and in the stathless cladding on the inside of the vessel where the hori-zontal ten-inch nozzle opening merges into the vertical vessel wal Northern States Power Company (NSP) opened the vessel and found cracks in the sparger unit, and further penetrant examination re-vealed cracks in the cladding Ls described in paragraph B. The

> licensee already had on order redesigned sparger units and thermal '

'leeves, because the problem of cracking in the sparger unit had been encountered in other BWR plant . Apparent Cause The licensee stated that excessive vibration existed in the sparger units, and the sparger unit failures were probably of a fatigue nature. The cracking of cladding in the nozzle area appeared to be

' caused by thernal fatigue. As originally designed, a thermal sleeve was fitted into the nozzle with a slip-type fit, which allowed some water flow around the outside of the sleev . Planned Design Change The redesign is set up for an interference fit, using a short length of Inconel pipe welded to stainless pipe in the interference area for a better match to the expansion and contraction thermal properties of the vessel. Other design changes to improve water mixing and to minimize cracking arci (1) junction box made up by welding two half forgings together instead of the original weldment; (2) increasing the thickness of the sparger pipe from five-inch, Schedule 40, to five-inch, Schedule 80; and (3) new design sparger pipe incorporates a singic row of holes of varying sizes directed at 900 to the core axis, instead of the old sparger pipe which had two rows of holes, with one row directed as above, and the other pointed down at an angl . Observations and Status The inspector was lowered to a working platform in the vessel to inspect the work donc up to Thursday, October 16,-1975. General

, Electric Company (CE) personnel had supplied the procedures and general plan of work. Using carbide burrs and air motors, they were grinding

'

areas shown by penetrant indications. The plan involved grinding 1/16 inch deep and a penetrant test, followed by a mapping plan of crayon marking so that the grinders would know the length of the indicatio It was decided on Friday, October 17, that the grinding of individual indications would be discontinued where the greatest concentration occurred, and that the entire area of indications would be removed with a grinding wheel. At the 1/4 inch depth of grinding (nominal thickness cladding) a nital etch would be employed to determine areas of stainless and areas of base metal remainin .

r-

.

.L_

..

.

,

In a telephone conversation on October 20, 1975, with the station superintendent, 15 cracks were reported still to exist in the four nozzles. He stated that measurements indicated a penetration of base metal in the deepest areas of 1/4 inch to 5/16 inc The inspector asked tac licensee if the authorized inspector (Hartford Steam Boilder Insurance Company) was knowledgeable of the situation, and he stated they wer The licensee stated that an outside review of the CE calculations and analyses would be made by an independent consultant. The intent is to 1 cave the area as ground and blended 4:1 edge Welding on the vessel is not a practical thing for large areas, particularly base meta The working conditions on this job are very difficult, since the exposure amounts to about 2R per hour, and full masks with breathing air are required. Over 200 outside men (boiler makers and pipe fitters) havc been trained (grinding and radiation protection) to date for this job.

.

e

_ _ _ _ _ . . .

_ _ _ _ _ . _ _ . . _ _ _ . . _ _ - - - - -

O s- O

'

1,

.

.

Kupper f%clou > '

'

.

i N ,

W' d l Ar du'iti, c<ala

.'/. // '

( +)~

~

Ts c ,.<ip, .a

-< < ,

- -

i - s i..u

'

I

\ .,i

'

l

.

.

/ i ,,,.,a

pn J .,.,+

N l//sp;.,.y,,,., /,., Ah nlc-a

/ff f';y u r e 1

- - , m m o . , . .. v v . ,,.; - .c ,

. .~ , , = y m

. -

.

.

.. .

.e4

 !" *

\

,

.~-l,

, .

' { 'p I

{'$)~ ,1 i l

-

I

[iy o t r

. .

. ,& --

, e, ..)n ?

$.2..As3 v( $

'

.

ts . /. . >-.. ,

,

'

i

- ..

'

s s. '\ .

.

. .a . . , , . .-

l; I ,' - " a .. y .

W ', ..

,n ,a. .. ) ('

.

-

\

,i * .., ;. . h.}r:

,

.

p M CW, , 4'Y

. : .4mnD, .. i:

.

.' ,.L it r p' .

.. :n. ..sf

.

/ o -

.

I t/ .

';

...

s'. . . .s ,~; . . -

t- l 4A. f

.. . g;. ~, g

. -

~

g -

. . .

t

r k

{ et

, J*.-

ss

'

' > fe-u . ,, -/. ;n,,\

. ,,;.h d d ,I b..b',en., A yNhMM /r.t**

y.v y g/ ( 3. .x

>

i s

- .

, 3.c. .

.:

- ..

, ::.:.0

.

': **# ,g g {p ,

.

4 s ,.*

,,  : .. -

(wh n' Iy a'[ *.: + .:.f.,' v *'s*:.

,,, 9

. p.:.. p.;Ag':hs

..

~

s, .i

,

' .-

.

.

... .,

.,.

g . s. s y p,,, . g j.,y

. . -

. ,. .. . ~.. ,

.,

, ,i

,

k,,,,

wuk  :. ; . ,2 .?

. .

\ .- -

- . '.Secter y '

.

.45%

.

s vl m Y%A ;;QN

.

m.&.;%a

.q " ,

,

.c

-

f..'. >

p

.

-

. . . ..

-

y't.,e % go y p Q

-

-

p  ;

,

cp;. h:(..? t T:W/

.=~ J-- $Q . J

/ ,<

' *

s* /

,

.

>

l yY.:. : l' J. ,/ /,/XlllN\"

y\..e

.

!

/ ,

,

,.. /% .. .

., l$11j

. . . .

.. .

. .. ..

.

. _ _ _ _