ML20072R781
| ML20072R781 | |
| Person / Time | |
|---|---|
| Site: | Saint Lucie  |
| Issue date: | 02/11/1991 |
| From: | GENERAL ELECTRIC CO. |
| To: | |
| Shared Package | |
| ML20072R774 | List: |
| References | |
| NUDOCS 9104080124 | |
| Download: ML20072R781 (7) | |
Text
GE Reguletory Svs TEL No, fie,r. 2 9. 91 15:51 P 03 FINAL REPORT OF GE TYPE AK 2 25 CIRCUIT BREAKER S/N 228A4389 200 8MG FAILURE AT FLORIDA POWER & LIGHT COMPANY'S ST. LUCIE NVCLEAR PLANT UNIT 1 l
L PREPARED BY GE NVCLEAR ENERGY l
NORCROSS, GEORGIA l
FEBRUARY 11, 1991 REVISION 1 l
=
l 9104090124 9103'29 PDR ADOCK 05000333 P
GE Reguletoru Evs TEL No, Jer 29 91 15:02 F,04 t
EVENTS Florida Power and Light's St. Lucie Nuclear Plant Unit i experienced a failure to close of a GE Type AK 25 circuit breaker used as a Reactor Trip Circuit Breaker.
The ensuing investigation revealed that the breaker operating springs had disengaged from the breaker mechanism and fallen out of the circuit breaker.
Subsequent inspection of the unit's other reactor trip breakers revealed that three (3) of the nine (9) circuit breakers contained operating springs that were not installed in the proper configura-tion.
The " failed" circuit breaker (serial number 228A4389 200-BMG) was shipped to the GE Apparatus Service Center (GE-ASC) in Chamblee, Georgia, for inspection and repair.
Upon inspection, one of the two springs returned with the breaker was found to be the incorrect spring.
The two (2) operating springs in the Type AK 2 25 circuit breakers should be mirror images of one another.
In this case, both springs were the same.
The circuit breaker is still in the Chamblee, Georgia, GE ASC awaiting overhaul.
The unit's other three (3) ciret.;. breakers (serial numbers 228A4389 200 2, 228A4389 200 9MG, and 228A4389 200 5RR) that contained operating springs in an improper configuration had the proper springs, but they were installed on the opposite sides of the breaker mechanism.
In other words, the spring that should have been installed on the right side of the circuit breaker was installed on the left side of the breaker and vice versa.
The springs on these breakers were still engaged within the circuit breaker mechanism ard the breakers were functioning properly.
OnNovember8,1990,thespringsonthesethree(3)breakerswereremovedand properly reinstalled on site OPERATIONAL IMPACI GE has conducted tests on the Type AK 25 circuit breakers to determine how the circuit breaker functions with various spring orientations, how the breaker functions with one or both springs missing, and what potentially causes the springs to disengage from the mechanism.
The results of these tests revealed the following:
1.
A circuit breaker that has successfully closed, and still has both springs in place, will trip regardless of the orientation of the springs.
2.
A circuit breaker with only one (1) spring in place can " operate" provided that the disengaged spring does not jam the inechanism.
l Witn only one spring in place, the circuit breaker mechanism will De t'rt 1%ch closed ed the main contact who on at least on_vphase will have significantly less wipe than the other two (2) phases.
l Depending or how ' heavy" the contact wipes were adjusted, the l
contacts could possibly not make contact at all.
Page 1 of 3 Pages 02/11/91
GE Regulatory Svs TEL No,
. Mar 29 91 15:52 P.05 t
3.
If e circuit breaker loses both operating springs, the breaker will..ot close.
4.
The actual spring configJration appears to be one of the factors affecting whether the spring (s) disengages or not.
Wnile a spring orientation (as shown in Figure 2 attached) appears to be less likely to disengage, the disengagement is not repeatable; therefore,nofirmconclusioncanbereached.(Thisconfiguration did not fail during the w aluation testing.)
5.
Since the spring disengagement cannot be reproduced with any certainty, the exact disengagement causo cannot be determined.
In the case of the " failed" reactor tri) breaker at.St. Lucie, prior to the reported failure, this circuit breaker ind functioned properly through four (4) years of plant operation and testing.
OTHER CONCERNS During the course of the investigation into the failure of the St. Lucie Unit 1 breaker, it was discovered that the operating springs were not current revision of(3) Unit 1 reactor trip bren(ers in accordance with the installed on three the GE drawing.
While investigating this apparent discrepancy, the following information was determined.
GE Type AK 25 Circuit Breakers have been manufactured since the 1940's.
During this time, many drawing revisions have been made.
Some of these drawing revisions were made to correct problems, some of the revisions were made to include more detail, some were made to reflect changes in material and/or processes, and some revisions were made to reflect changes in manufacturing practices.
l In the case of the circuit breaker operating springs, a drawing revision (Revision 6) was made in late 1985 to reflect in the drawing the
) referred manufacturing installation orientation of springs during the manufacturing process. _ In essence, this change rolled each spring 180* longitudinally and, as a result of this roll, swapped the left hand spring to the right side of the breaker and the right hand spring to the left side of the-breaker in order to retain the correct orientation and operation of the springs.
This new spring orientation is shown in Figure I while the older orientation is shown in Figure 2.
In either orientation, the intent is for the curve between the spring hook and the first spring coil to curve away from the centerline of the clrcuit breaker.
i l
l Page 2 of 3 Pages 02/ll/91
GE Regulatory Ev!
TEL No.
Mer,A9 91 15:E!
FM 9
GMCLU$10N5 1.
An incorrect operating spring was installed in a St. Lucie
" failed" circuit breaker.
This incorrect spring is believed to have been installed inadvertently by GE at the GL.ASC in 1986.
2.
Three (3) St. Lucie Unit 1 Reactor Trip Breakers contained operating springs installed improperly.
These improperly installed springs were also apparently installed by GE in March, 1983(2 breakers)andinApril,1989(1 breaker).
3.
This failure of the St. Lucie Reactor Trip Breaker to close is not a safety concern because testing has revealed that the circuit breaker will not close unless the operating springs are in position.
When the breaker is being closed or is closed, the spring tension keeps the springs in - tir position in the mechanism.
Therefore, if the breaker C ses, it will open when required to fulfill its safety function in the plant.
4.
The actual orientation of the springs is satisfactory if they are installed in &ccordtnce with either Figure 1 or Figure 2.
5.
This failure occurrence points out a potential for a common cause error involving incorrect selection of the spring during breaker assembly.
However, the conseguent breaker f ailure appears to be random. The St. Lucie ' failed brtaker in fact o>erated operly and passed all functional tests for a perico of four (
years prior to failure.
CORRECTION ACTIM$
1.
The three (3) St. Lucie Unit 1 Reactcr Tri) Breakers with improperly oriented springs were " corrected" on iovember 8,1990.
2.
A specific checkpoint has been added to the AK 25 overhaul and maintenance processes to ensure that the operating springs are properly oriented in the breaker mechanisms.
Page 3 of 3 Pages 02/11/91
P, FIGURE I (Revised)
E
'.T
+
)
9 f
=
D
{Yf
\\
+
7 lllt Q
l i
l-c c'
l G rn
=
I f
i 3
f Arb
.?
fI fI v I' v __ u ;lJ I
8 y-i7@
l ll 1
I j
t i 1 I
b
'O C
{
I FRONT OF A
in I
g
.((
BREAKER f
8
~'
a a
s r
. f i
h 3 j t
I N
,k, 1
1
-ea i
DJ l
).#
, {}.
e i
.o J
n
',_.w t
??
1 A
3 2/11/91
1 GE Regulatory Svs TEL No.
-. M a. r. 2 9 9 9 1 15:54 P.08 e
i O
SE h i
b; a
f I C
y M
p,
(
O e
s
/
k g.
)
4 g M h
-)-
- - ~,, ',.)
r
(
- ~' )
p g
q w
~
~ ~
,,66 g
g e
w 4
N
=
=__
l I
VIEW "A"
'E' l
j.
t g/'.N '
a
._.s k
E$
Va9 J
y 1
l
GE Regulateru Svs TEL No.
.,Jia r, 29. 91 15 : 51 P.01
-+ rn e gnov os l'Cr + Y e 9
l Car nr GENaciewEnergy Date 3 29-9I To
__ 'O Anlda (nallCYrrlidYY) Q-Dis 5
x This pageplus& page(s)
From hof/ dim /17/R Mali code 187 Nuc car @roducts Lisnsing 175 Curtner Avenue San Jose, CA 95125 Phone 8'425 _ NIS FAX 8'425-4458 or (408) 925-1914 or (408) 925-4458 Subject Message I
4 l
l l
l
.. - _