ML20087K210

Forwards Safety Evaluation of Damaged Control Rod Guide Tube Support Pins.Ut Indictions on shank-to-collar Not Safety Concern

ML20087K210
Person / Time
Site:	Point Beach
Issue date:	03/19/1984
From:	Fay C WISCONSIN ELECTRIC POWER CO.
To:	Harold Denton, John Miller Office of Nuclear Reactor Regulation
Shared Package
ML20087K212	List: ML20087K210 ML20087K216
References
TAC-54356, NUDOCS 8403260072
Download: ML20087K210 (17)

Text

l N%SC00 Sin Electnc ma come 231 W. MICHIGAN, P.O. BOX 2046. MILWAUKEE, WI $3201 March 19, 1984 M r . II. R. Denton, Director Office of Nuclear Reactor Regulation U. S. NUCLEAR REGULATORY COMMISSION Washington, D. C. 20555 Attention: Mr. J. R. Miller, Chief Operating Reactors, Branch 3 Gentlemen:

DOCKET 50-266 SAFETY EVALUATION OF DAMAGED CRGT SUPPORT PINS POINT BEACil NUCLEAR PLANT, UNIT 1 During a meeting with members of your staff on March 8, 1984, Messrs. Burstein and Fay provided a copy of Wisconsin Electric's safety evaluation of damaged control rod guide tube (CRGT) support pins at the Point Beach Nuclear Plant, Unit 1.

In response to a request from Mr. Colburn of your staff, we are forrally providing an additional copy of this evaluation as an attachment to this letter.

Very truly yours,

/

, C

/

O&J Vice President-Nuclear Power

C. W. Fay l

l Attachment l

Copy to NRC Resident Inspector 8403260072 840319 gDRADOCK 05000266 I PDR

o

• e.

March 6, 1984 Mr. R. A. Newton /NES File PT 3.2.2 SAFETY EVALUATION OF DAMAGED CRGT SUPPORT PINS AT POINT BEACH NUCLEAR PLANT, UNIT f The thirty-seven (37) control rod guide tubes (CRGTs) at PBNP, Unit 1, each contain two support pins (also called " split" pins) located at i the bottom flange of the lower guide tube. The support pins horizontally align the bottom end of the guide tube at the upper core plate relative to the fuel assembly and provide lateral support for the guide tube against reactor coolant system flow and other forces (see Figures 1, 2, 3, and 4).

The CRGTs provide lateral alignment and support for the Rod Cluster Control Assemblies (RCCAs) when the RCCAs are withdrawn from the core (see Figure 5). The support pin design allows removal of the CRGT from the upper internals and accomodates axial thennal expansion relative to the upper internal support columns (see Figure 6). The support pins each consist of a partially threaded shank, a collar, and a dual-leaf spring. The pins are bolted into the lower CRGT flange using a sleeve nut with a locking disk and pin. The leaf spring of each pin fits into a hole in the upper core support plate.

The support pin assemblies are constructed of Inconel X-750 material, which has been heat treated and age hardened.

In Westinghouse letter WEP-79-524 dated April 4, 1979, it was reported that a CRGT support pin was found broken and a significant number of pins had UT indications of cracks at a Japanese PWR plant built by Mitsubishi Heavy Industries. No problem with support pins.at Westinghouse plants had been reported at that time, and Westinghouse judged the failures not to be a safety issue. In Wcstinghouse letters WEP-82-536 and 543 dated July 1 and 22, 1982, it was reported that support pin cracking occurred at a domestic Westinghouse plant (North Anna 1) for the'first time and the potential existed for stress corrosion cracking of the support pins at PBNP, Unit 1, due to the heat treatment of the pins at less than 1800*F. In NRC IE Information Notice 82-29, " Control Rod Drive (CRD) Guide Tube Support Pin Failures at Westinghouse PWRs," dated July 23, 1982, similar support pin failures were reported at Westinghouse-designed plants in Japan and France. .

Westinghouse's position was that a cracked or broken support pin did not constitute a safety concern, however, an inspection of the pins was rec-omended at the next convenient outage for PBNP, Unit 1.

An ultrasonic inspection of the CRGT suppcrt pins at PBNP, Unit 1, was recently completed. The inspection revealed UT indications in the

! shank-to-collar region of 67 of 74 support pins (i.e.,~90%) (see Figure 7).

No indications were found in the support pin leaves. A subsequent visual inspection of the sleeve nuts and threaded shank portion of the support pin assembly revealej three missing nuts and shanks (one each on the CRGTs above core positions G-3, I-5 and K-7) (see Figure 8). Visual inspection of.the peripheral portion of the upper core support plate (the inner portions are essentially inaccessible), the core former plate just below the upper core support plate, the lower core plate, the lower portion of the reactor vessel, (see Figure 9) and all upper nozzles of fuel assemblies (see Figure

10) discharged during this outage (the full core) and the previous outage i did not locate the missing portions of the pins. Visual inspections of the

. Fot leg side of both steam generator channel heads to search for the missing

. parts are planned prior to Unit I startup.

Westinghouse has performed an evaluation of the ability of both Point Beach units to start up and continue safe operation with brobn CRGT support pins. ' believe that two potential safety concerns must be addressed to justify safe startup and continued operation with the three missing CRGT

, support pin nuts and shanks and the potential for additional support pin breakage during operation. These potential concerns are missalignment of the CRGT which could prevent RCCA insertion and adverse effects on safety-related components resulting from loose support pin parts in the reactor coolant and connected auxiliary systems.

The first potential safety concern is that broken CRGT support pins could prevent RCCA insertion due to lateral misalignment of the bottom of the CRGT with respect to the upper core plate. Westinghouse analysis shows that, if both support pins in the same guide tube are broken at the shank-to-collar interface and at both leaves (where previous experience at the other plants has shown cracking) "no safety concern with respect to control rod guide tube misalignment is identified relative to safe shutdown of the reactor with control rod insertion." Westinghouse analysis shows that, even if all support pin assemblies are completely missing, the CRGT alignment will be maintained sufficiently by the adjacent support columns, flow mixers, and orifice plates on the upper core plate such that "the re-quired Technical Specification rod drop time of 1.8 seconds will be met." In addition, a review of RCCA rod wear and rod scram time trends over eleven fuel cycles have not indicated any CRGT misalignment problem. The biweekly rod stepping tests performed during operation per Technical Specifications should indicate any significant CRGT misalignment during the next fuel cycle. Therefore, the potential for the misalignment of CRGTs resulting from broken support pins preventing RCCA insertion is judged not to be a safety concern.

The second potential safety concern is that loose parts from broken support pins may cause adverse effects on safety-related components in or connected to the reactor coolant system. Westinghouse has analyzed a loose support pin part effecting RCCA insertion and stated that "it is considered an extremely remote possibility that any loose part could effect all the '

movements and placements necessary to affect RCCA movement." In addition, the reactor can be safely shutdown with the highest worth control rod stuck in the fully withdrawn position. If loose support pin parts enter the steam generator channel heads, the only scenario which could effect' safety is the extremely remote possibility that a support pin shank separates from the nut, enters a row 1 tube (43% of the tubes), gets captured in the U-bend, and vibrates over time causing fretting and eventual small localized tube leakage. The plant is designed for a single double-ended tube rupture so the above scenario is judged not to be a safety concern. Adverse effects of loose parts on the reactor coolant pumps are not expected, since the loose parts should pass through the pump. The remote possibility of a locked rotor accident resulting from a loose part has already been analyzed in the PBNP FSAR. The adverse effects of loose parts on the reactor internals would only be a concern if large numbers of broken support pin shanks separate from the nut, travel to the lower part of the reactor vessel and land under the secondary core support energy absorbers during cold conditions.

The resulting wedging effccts on the lower internals during heatup were

' found by Westinghouse to be acceptable using conservative criteria unless an

- incredible nunter of shanks were wedged there simultaneously (six under each support or ten under one support). Note that only three shanks are now missing snd they are not located in the bottom of the vessel as verified by a visual search.

The effects of loose parts on auxiliary systems or coniponents was also reviewed (see attached table) and the RHR system was the only connected system which could be significantly affected. The RHR system valves could not be held shut by loose parts so RHR system startup could be initiated by opening valves. RHR isolation valves held open by loose parts would be detected upon heatup. The RHR pumps are expected to pass loose parts through without seizure but the parts could cause some damage to the impeller. Loose parts in a heat exchanger could result in a tube leak but this would be detected by leakage into the component cooling water system.

Since redundant RHR pumps and heat exchangers are provided, the components are accessible for repair if degraded system operation is detected and safety injection pumps or the steam generators are available for alternate methods of core decay heat removal, the potential effects of loose parts in the RHR system are judged not to be a safety concern. Therefore, the potential effects of loose CRGT support pins parts is judged not be a concern for any safety function.

In conclusion, the UT indications on the shank-to-collar region of the CRGT support pins and the three missing support pin nuts and shanks at PBNP, Unit 1, are judged not to be a safety concern due either to CRGT misalignment preventing RCCA insertion or the adverse effects of loose parts on safety systems and components. This problem does not represent a violation i

or require a change to the PBNP Technical Specifications or involve an unreviewed safety question. I believe that the above evaluation with the i attached evaluation from Westinghouse justifies the safe startup and continued l operation of PBNP, Unit 1, for at least one additional fuel cycle. It is l assumed that the normal startup RCCA tests (rod drops and stepping tests) and the biweekly RCCA stepping tests required by the Technical Specifications continue to show free RCCA movement. It is also assumed that RHR system isolation is verified during plant heatup to ensure that loose parts are not captured in the isolation valves. Although the results of this evaluation generally apply to PBNP, Unit 2, also, the support pins on Unit 2 had a -

higher heat treatment temperature of 1950*F and stress corrosion cracking of 1 these pins is not expected. I

p. m ~

RKH: nun R. K. Hanneman l Attachments cc: Messrs. C. W. Fay J. J. Zach A7 W Approved:

'R. A. Newton

TABLE PENETRATIONS AND COMP 0NENTS IN REACTOR COOLANT LOOPS AND THE POTENTIAL EFFECTS OF LOOSE PARTS IN THE RCS Penetration Description Comments I. Hot Leg A. 1-TW450B & 451B Hot Leg Loop RTD No opening to coolant; (loops A&B, resp.) Thermowell Not a loose parts concern B. 6"-RC-2501.R-6&9 Capped Vent Pipe; No safety function and (Loops A&B, resp.) Taps into top of pipe capped; Not a loose parts concern C. 10"-RC-2501R-16 RHR Suction Line; Taps Loose parts could travel (Loop A only) into botto'n of pipe at to RHR pumps and/or 45* angle; 2' vertical HXs; No loose part run downward (1-PT420 problem expected on taps off here); 8' 1-PT420 since no flow horizontal run (Excess exists into that small Letdown taps off horizontal tap; Excess bottom), 18' vertical Letdown is not safety run upward related so this is not a loose parts concern D. 10"-RC-2501R-2 Pressurizer Surge Line; Locse part not expected (Loop B only) Tops into top of pipe; to travel upward into this 3' vertical run upward tap since flow into pipe is usually low or nonexistent; No safety related function function could be affected anyway.

E. 2"-RC-2501-14 Hot Leg Bypass RTD Inlet nozzles with a number (Loops A&B) Supply Lines; ? 1" of small holes are used for taps into pipe 120* each tap; Not a loose parts apart, concern.

[ F. 1"-RC-2501R-14 Hot Leg Sample Connec- Taps into top of pipe,

! (Loop B only) tion; Taps into top of flow-rate is low and not pipe safety-related; Not a loose parts concern G. 4"-RC-2501R-14 Isolated and Blank- Isolated and not safety-(Loops A&B) Flanged Vent / Drain related: Not a loose parts Line concern H. Steam Generator U-tubes are 3/4" I.D.; Loose parts (% 3/4") should l (LoopsA&B) 3/4" drain lines are pass right through U-tubes 1

~.

, isolated without causing significant '

, damage; PBNP is designed for l tube rupture; Drain lines are not safety related II. Crossover Leg A. 3"-RC-2501R-14 Hot and Cold Leg By- Flow is into pipe from (Loops A&B) pass RTD Return; Taps top; Not a loose parts into top of pipe concern B. 8" 2"-RC-2501R-10 CVCS Letdown Line; Loose flexure head would (Loop B only) Taps into bottom of probably get trapped by a pipe letdown orifice; Not safety-related; Not a loose parts concern C. 2"-RC-2501R-14 Excess Letdown Line; Not safety-related; (LoopsA&B) 1-LT447 taps into line Not a loose parts concern D. 3/4"-RC-2501R-14 Taps (4) for RCS Taps are perpendicular (Loops A&B) Flow and Wide Range to the flow stream; no Pressure Transmitters; flow into the small taps; Taps come off either Loose part would probably side of 90 elbow be detected by unusual flow perpendicular to flow or pressure readings; stream Redundant flow transmitters are provided off each loop (only one loop required for Rxtrip); Not a loose parts concern E. Reactor Coolant Centrifugal Pump; Loose parts are expected to Pumps Control Leakage Seal to pass through; Potential locked rotor due to loose part has been analyzed; Parts are too large to go through seal; Not a loose parts concern III. Cold Leg A. 3" RC-250lR-1 Pressurizer Spray Line;Not expected to collect (Loops A&B) Taps into the top of loose parts since it taps the pipe and has at in top and flow rate is low; least a 3' vertical Not safety related; Not a run upward ward loose parts concern.

B. 3"-RC-2501R-12 CVCS Charging Line; Flow is into top of loop (Loop A only) Taps into top (45 off piping; Not a loose parts vertical) concern C. 10"-RC-250lR-7&8 Safety Injection Acc- Flow is into top of pipe; (Loops A&B, re- cumulator Supply Line Not a loose parts connection spectively) (also RHR return on Loop B); Taps into top

. of the pip 2 has at least a l' vertical run and a check valve in horizontal run D. 2"-RC-250lR-14 Col.1 Leg Bypass RTD Taps off top of pipe and (LoopsA&B) Surr ly Line; Taps off flow rate is low; Not a top (approximatel loose parts concern 45' off vertical)y E. 2"-RC-2501R-11 Auxiliary Charging Flow is into pipe and not Line safety related; Not a loose parts concern j F. 1-TE450A & 451A Cold Leg Loop RTD No opening to coolant; Not Thermowell a loose parts concern IV. Reactor Vessel A. Instrument Thimble Thimble guide tube Penetrations are always Guide Penetration penetrations into filled with guide tubes; bottom of vessel Not safety related; Not a ,

loose parts concern B. 4"-RC-2501R Safety Injection Flow is into vessel; Taps Vessel Injection horizontally into vessel Lines; Taps into side well above the core; Not a of reactor vessel loose parts concern C. 3/4"-RC-2501R-14 Reactor Coolant System Taps into top of reactor; Gas Vent; Taps into Flows are too low to pull top of reactor vessel loose part into line; Not a head loose parts concern l

l

. 9). O 1, '

4 i  !

l i

4 p+ 4i e <-- a V *f j

c.oero 0 NE MChaiensM soo e

D .s.re,u,,r n, ro, gg,g g g , ,./ 9P K. Q.? f7 sN ',f t i Closv.t 68 A0 o" e yo >

lo/ h '( 'N ' :h A5MM8tv p()  !. d N$,D N [' '*'

• suivt

-.. . wm. , 9e (f '

,, . ; P c 9 k c'M

,3 g .g

'" ~

rn'A';"& ;.mh, j__),u]

4 7 m, weetuou 7W% A3,f'

. =s T , . ,.

%c  ! ,

. . . _ I'I. Q- i -

+  % -z ,) *** 5*5

%7 p iyw, .nc , ,,,,

_.i.....

Dt;} yd{

[

[

f;d;Q~77Q,,,,, ,,,,,,,_,,, ,,,,,, r twm emenusun

~"-""

x ur' e e. M .f; h .c tag ) 's. "'"'*""

g Mit) c Ig -i{ a e.

i le Q og{d[ ;144 h.M .

+ '^p(4 $/

u . < ,c .i .n L M' ,;pG E

5. 1 'T -[p i = s.... o i

, I l

l l

sI; 's y.

..g- /

l y y nuu n i e ar .o ve u,i  % i l D% ,

y eanianao<at w eost N

N aum m i h

9 k d,,4 h,

4 j;

I NJ 4,gsw d+jv % ,

9 s;,

4 is .. ' 5 ,a y, s l {\h. -

. . . l t W ,,umin ro.e pia n

. n ., s. = >  :

s -3 N\ .

T ,

h,

,,.{yv.+j N

s g; k ,k n t

P i. ';

g 1 S[E,hrd .if2N

..,n w , nrm w .cian

,n,y -

-m= *co."'u o i.., t < 4 ..

et (

I.l; .f[._i,'tt _ i., [_!, .

'**d

i. . .-,at '*"Tw a'e= '

itEACTOlt VESSEL INTERNALS i

FIGURE 1 i

t

. .i M/#/##H/WMHH/#/MA i UPPER SUPPORT

• ' PLATE in cz is i

ris I

f i a

i 13C214 ,

d 13 C3 la 86.15 Ii4TER!!ECI ATE

, I i

GUIDE TUBE t

ASSEiiBLY l -

9 2ir

.JL

$ 12.00 (CL3 li

, 9.625 l .

3r ir 1-  !. ;L n i i LOWER GUIDE 0',875 7

TUBE ASSE!!BLY

/  ;

i 32.5 n

9.00 n

T 9.00 3 r n UPPER CORE PLATE

,, 7 #2s . .

T Y// ////// / //// / / f / /// / / / // / / / / / / /L FIGURE 2

~

. ~.

p ;] i  ! i l

i'd ] i T , I by L.J LJ s I i um- --

I l

, , L0llER GUIDE TUBE ASSEMBLY SECTION l

,j g

. II O ,

, . i

.m I) 11

), 5 il 9

)ll 11 l

wi i

@ j lit (1 J

_m

( _ _ _ . . _ . .

. FIGURE 3

51- --

. 5, .  !

=

'(

GUIDE TUSE BOTTOM FLANGE .

( NUT i_ , , . _ . , s_

_ -r, LOCKING PIN g _~ _

' LOCKING DISC h

W 3: , 0. 2

hl f b == IEK 1 L , , /t C01.t.AR 1

i } V/A

[ , \

. 0.1 "

l_

Ny

.g (max,coldandat

,i operatingtemperature)  ;

2 CU l

I i

UPPER CORE PLA NtN i

l i

l GUIDE TUBE SUPPORT PIN

,. FIGURE 4 l

__ J

m A_ a- - . . - + a --._A. - .

- -.r a a-- - - - - - - - -- -..- -

G 9

e l

l

.t

_< . x o,,40,*oo 6

- ' s "7 ~ -

^

Ass,Neip

.1 y_

v

/ .,*

1. 00 y **so 4,.

o5 . :hl \44, f_:;v,y.*g/, , i

+

g,%R'$k;'.K

.;g

'? .

9,, #0c

/

,*$'*o y ,,Y,

\

x.'-

n);q, rp$ '*1 m8, .!s, #Og

$V f-

• j'h>

/ 5f,s~w%

i '

N. ,

W

^

.s #44 -

jll f

,} fi f< it ~,,

44s. #of

.,o'o+

f: '  %

+o p- /

s/r . I,

- NOy, / O'>j 5 // ' ?)

O/ < < , , 47,' / J- /

~ ,

p s ,

5 Y 8 L

• . 5 B o

', 8 S M

E 10 YN E R

LI S O

BP 0 S C M A EG 6 SN RE SI T ET AT 2 FA A R6 FI LC O t' F

'EO LL PE

- F PR y

~

, * , L 7 dD UU SG Aq,M I

4 h- C C9 4N 4 - EF i

i

- - r-X 1 1 R

O 1

i t j

i I t i i i C 1 I i

1 7 i R

g - _

E

- P 1 i ( -

I l L L t

1 ] I l i I I 1 P

_ ~ ' U I _ .

I I g i r i i 1

1 ,

l i 1 1 t t 1

- _ I I t t I L J

_I I _I I i 1

. 1_ _

' _ J_

I , I f r __ f* _

I ,

e T

I , _ I 1 3 i _

i i 5

- I t I i t L

- ' L t .  ? I ~

J. ] I

- )

1 1 L

O _

-1

~ ~~ _

C

_(

~

t

. r [ i i _

T R

O 7

l I i - 1 U'

'- a ~i 7 ~i P E_ i

~

~ L I I t I l  !

F

_ 1

- J_ I L

~

i J

~ J 1 S -

i i

8 L F I ,

t I

C i r I i t

2 f I t t L I

/ 0

/ j 2 1

E gl ,

T _ i l A

L P

T R

O P -

P S'

3 E

F F

r

,3 p s -N- 4

" W .l

~

- 4h ' G g eA- +- I .

" M A

E B

- 0 5 -

9 s

i 5

5 l

l 6

1 2

1

1 . . . .

M

, . ,1 i

' ew, l l -

i nw4 -

w) mo v 5

pgq .

Dowel Pin

==< '

y

't I  % 1

- se o 7 Locking Device Support

'i

[-

! ,,, lPinNut' y <( .

h0/

'=' '

_ / '

l9

• • ' l' Crack Potential' .

• h' . l i Locatio N c i .

g g,, g g ,

x .n g,= N q.. .

\,l i . _1 .

-l '

Support

f .e

/,/. o

.. Pio , c- ,

- /.

/

. (Spring Pin)

Leaf Upper com Plate GUIDE TUBE ASSEMBLY I FIGURE 7 l

e e

e I

J J

210*

A A Outlet A

O O O c O O -  ;

O O O O O '

O =

0 O O ,

v'r @ O O O O O O O O -

1 O @ O O O >

a i

O O e i i

O @ O .

3; L

90*

x I

1 2 3 4 5 6 7 8 9 10 11 12 13 Control Rod Guide Tube Locations CRGTs with a Missing Split Pin Nut .

FIGURE 8 -

i

.:_.. . -. -. - - - --- --- - - - ---- ~^- ~

I i

. l.

}

il hl] k I ,

I Ie &  % n 5 & ql2 \ it!\

lll 5 "I.

I 4 i

< Qa rb {n :F7 F1 $

7 py x ,

s s, i -

g 1 A .7 i .

[

J_d L_L;1,!; ,1 Jit I sMl pc!t- sq

.x i -

a$ p p-G l.9, h ,, .

gj ij

+y .aww -

t -

Nxc0 uy

lc* ,

i

. . s .

l ig

_i u- _ a j;E i 3 .

3.p i  :.

k p p- err. .a , l

% 3 ,

$nd wcL=

l3n; -

x.l l

dJ13-i dt,3d L

< pl -

g -[ej e:.jn v,: :de c<a...c.a ude,:6:<x.j:!-5:. e:.-pabfNQ NN

- s :

/

^%

N i

i

Qs j

% / ->\J 's

), \!~! N

/

/

/

l /

/

/

/

/ .

/

/

/

/

/

/

/

/

/ qw

/ s 5

/ 1 i 3.

f/ 1mi ut rs:

. ara:r.an n

d

~

/ )

• O O @ l' f- -l

'. xnxt 7 =-?n!:ms t  :-g=q 4

. .i r \ .

\ .

9-  ;

_il

b. . i

[ .

n i

s I

f

~

A75 0l A REF * -- 7.763 50 RE F -+

[' 0

. 0 875 00 A RE F g i E ,D if o I"'

4500 REF _

pg

' 31.

7 763 SO AIE 6 805 g

g

. . m

' M""1 ' p._sl_.-

TOP VIEW 1 4 90110a4 Vitw

+---

TOP NO22LE 151.850 rue t =o tE=oin -

FUEL ROO Grip AtEM9tY SOTTDet NO22tt hk!!kh!kkffkh!k!Ifhkk ==18448 MF W13L30 REF e- 10019 RE F *-8100REF e-ESSIREF e- 30.SE REF +- tels RE F ---,

^

100.719 REF _

Standard 14x14 Fuel Assenbly Outline FIGURE 10 /

. _ _ _ _ _ - - _ _ _ _ _ - _ _ _ _ _ _ - - _ -__ _ _ _ _ _