ML19305B432
| ML19305B432 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee File:NorthStar Vermont Yankee icon.png |
| Issue date: | 12/13/1972 |
| From: | Rosalyn Jones VERMONT YANKEE NUCLEAR POWER CORP. |
| To: | US ATOMIC ENERGY COMMISSION (AEC) |
| Shared Package | |
| ML19305B431 | List: |
| References | |
| VYV-2364, NUDOCS 8003190645 | |
| Download: ML19305B432 (6) | |
Text
, _ _ _ _ _ - _ - - _ -. _ _
EVENTS Rasponse to USNRC Letter, dated 12/13/79, Ippol.ito to Groce Switchyard Aux. Trans.
Startup Full Load Opening of Loss of
)
Relay Fire Trans.
Reject 81-1T ACB Startup Testing Diff. Trip Test Trans.
Date 5/4/72 11/8/72 12/27/72 3/29/74 3/17/75 6/4/75 No. of Circuits Lost The 115 KV The Aux. Transformer The Startup The 345 KV The 345 KV The 115 KV During Event System System Transformer Supply Supply Supply Cause of Event Switchyard Shutdown from Outside Startup Turbine Trip Operator error-Startup Relay of Control Room test, Transformer resulted in wrong breaker Transformer Testing failure of auto load Differential loss of manually opened internal transfer s/u trip while it station fault transformer, phase im-was supplying power during balance across Aux.
in-plant a Full Load Transformer J.oads Test.
(Cir-cuitry has since been modified).
Why other Lines Did The Testing The phase imbalance The other No other No other systems No other Not Fail When Others associated was only seen across lines, were systems affected systems Did with 115 KV the Aux. Transformer unaffected by affected affected breakers transient.
only The Aux.
Trans was unavailable due to event of 11/8/72 Voltage Increase No Yes - see Reference (3)
No No No No or Decrease Frequency Decay Prior No Data unavailable No No No No to Event, etc.
Y av i e
o C cuit 22 minutes
&OO&4 0677
,7. /. L/
a 5 /. O Vsm.n uvi' Y;.a::: am IK a o.ma i mzM.e : 'oime::/.Tiox SCVCNTY rrvCH Of tOVc GTettCT MtJTLAND, VERMONT O,;OI REPLY TO:
VYV-2364 P. o. sox m Vri4NON, YF.RMONT of.iOs4
)
5~
.d T '"
r nece ber 13, 1072
. : o ;.
1 L
P
'.SW
'i
.,..~e
....J e
.P 1'?
1.-}. '
^
i
~ /S/*/3
~ i(IMJ
/
Dircctar
,JU/h2.f h28 !
Directorate of Licensing
. United States Atomic Energy Cornicsi.on...
k'ashington, D.C.
20545 Cu.
10:FEPJ.MCE:
Operating License DPR-28 Docket No. 50-271
Dear Sir:
This letter is to provide you-ws-thet :itchrternatien concerning the incident reported in ny initial report dared 9 Novenber 1972 (VYV-2327).
Da Uovember 8,1972 the Unit Auxiliary Transformer was extensively damaged by fjrc.
The incident occurred approximately three ninutes after a reactor scrcu, executed as the initlal step of a shucdovn fron outside the Control Room which was being perforned in conjunction with the Startup Test Progrcn. Reconstruction of the incident utilizing conputer printouts, recorder charto, and reports of participatin:; personnel (refer to enclorure 1) fixed the orJgin of the prob 1cn cs a mechanical failure of a limit suitch f
arm on No. 2 Turbine Stop Valve.
This prevented generator lock-cut uhen the turbine was tripped and also prevented autematic transfer of in-plent Joads to the Startup Transforntr. The generator was manually isolated frou the syntcm by opening the tie brechcra in the 345 KV Switchyard.
The generator began to coast doun and the decreasing trcquency caused over-cxcitation of the Unit Auxilicry Trcusformer. The exciter fic]d breaker falled to trip during the under-f requency condition because tuo let.ds to the volts / hertz relay were not securely connected to the terninal board at the. back of the relay. At a point when generator frequency was significantly lens than systen frequency, the in-plant loads were manually transferred from the Unit Auxiliary Transforner to the Startep Transforner. This cauned a monentary application of syr. ten frequency to the Unit Aun111ary Transforner.
Apparently, this nomentary frequency mismatch, tehile the trannformer was under the stress of overc.xcitation, caused the failure of the transformer.
On-nite anniwnnent of dresar,e to the tranc.f arner on t.he fella ing dt; revealed th..:. it tas enreatic3'.y a tural f wr Thr-unit ces retuined to
?
thi* 1.stillidatf l u rQT for c.*Colual3r.n T.9d GUIV;U,c, 10. the. 4Qg_f' "QMO.
- Ji Ca
- I' IralluiorT/.'r Illifi heen ordi*r**d und 5 8 C).pOCTCd in A]eri, lp /.i. '
i
'Y h
I D"D D
5 wA A1
=
i..
virt:MONT W.;;.;G NtfCt.6 Mn r'CWC. C.c:nrCawli f 4,
s 4.
i
. Directorate of Licensing Decenber 13, 1,972 Page 2.
4
+
Based.upon initini investigation, a progran was developed to: a) evaluate the extent of possibic equipnent danage, b) inplcnent corrective action as necessary, c) preclude recurrence of the incident and d) provide adequate
- assurance that plant operations could be safely continued.
Sajient features of thin progren included the follouins:
1.
Cleaned up debris and renoved danaged transformer 2.
Dobic Tested the Main Transformer and collected and analy=cd oil
-(mE samples on the Main and Startup Transfori:crs 3.
Inspected all c,ntrol cable to Main Transforner 4.
Inspected 345 KV dead end insulators and inspected bussing j
5.
Inspected generator stator end-turns and slots 6.
Checked all relaying associated with the generator lockout relay 7.
Dobic Tested the Main Generator 8.
Inspected bus ducts and bussing 9.
Inspected breakers 12 and 22 av.
neggerce all notors on rne 4 KV hunsas 11.
Modified the Stop Valve Collars and replaced danaged linit suitch 12.
Inspected and verified satisfactory operation of all Stop Valve linit suitches 13.
Repaired and tested the volts / hertz relay 14.
Modified applicabic Plant Operating Procedures.
4 E::ecution of the individual steps involved in satisfactory conpletion I f!@
.of the progran outlined above began on 9 November 1972 and extended to j
22 Nevenber.
On 20 Novenber 1972 all significant test resultc had been obtained and there was cicar evidence that danege had been linited to th:
Unit ' Auxiliary Transformer only and all other associated plant equipment was in satisfactory operating. condition. At a necting of appropriate conpeny
.and vendor personne).it was concluded that plant operations could be conducted with reasonabic assurance that en incident of this nature would not reoccur.
1 It is gernane to point out that a 4360-volt pouer'line from the adjacent
. Vernon liydrocicctric Station nay also be connected to the station switchacar and is a source of off site cicctrical pouer in addition to that provided by the Startup Transforner.
t
~.. -.
,,,, ~
- v..
P r v/ : J e etc tJuct.'r,.t : Power e.a i, pc,,.wi :
Di rec tora:.c of 1.tcens ing, Decenber 13, 1972 Page 3 Preparation f or utartup was begun 21 !!avenber and Vernont Yanhec returned to pouer operat'.on 22 !!ovenber.
Very truly yourn, VERITO:!T YA!!!U:E Nt'CI. EAR l'O'..'Eli CORPOP AT TOM i
/,, s.
i i
(
RobertF.J$nes Plant Superintendent DilE/rlib (M-Q m.
i:nclosure 1
}
f.EDT."CC OF EVU::TH
) rADTNC' TO 1,02; 0F 'li:6 At:.;il.i A>:Y _T.m.'WO::TM 11/8/T:
t p:le Event 1440:31 Manual scran frc:a Cont rol 'Roen 1441:11 Stop valves closed as a result of H3.nh Moisture Separator Lcyc1 Trip.
Eypass valves opened to nalntain pressure.
1441:20 Turbine tripped manually in the Control Room and at the front standard.
Although the turbine was tripped it -indicated that it was still on.the line as #2 stop valve lights indicated " intermediate" and RPM vas holding at 1800. A further look showed the load comini; cff the unchine indicating that it had to be disconnected.
1441:27 Breakers 379T and 381T uere opened manually --RPM and frequency began to decrease 1:=cdiately.
1442:05 RPS MC sets tripped on under frequency (54H::) at s1620 rpm.
Recirc MG sets tripped. Voltage / Hertz reJay failed to operate.
1442:07 MSIV's closed as did all Group I through V isolation valves.
1442:19 Fu pu:np tripped on high reacto uater level, 49".
1443rli nreaxer 1.s uns closea paraliciang tne start-up trannterrnr with the Auxiliary Transformer, the latter being at 436H::
1443:22-Auxiliary Transformer High Pressure Fault.
Generator Backup Relay tripped.
1443 (From-
" Word" passed on public address system " Fire in Transformer" Security Log) 1443:22 Breakers 12 & 22 opened auto. Generator field breaker opened.
1443:26 Breaker 4T2 auto opcned 1443:26-Breaker 23 closed manually 1443:31.
Diesel generator "A" started " auto" and picked up bus 4.
(All. times from this point are appro>:imate, based on lo;; entrics, recorder charts and computer print-outs.)
- 1444 Diosc1 generator i'B" started manually and paralled to bus 3.
p 3T1 breaker opened unnually.
i 1444 Brattleboro and'Vernon Fire Depart:1cnts called.
r-Dry pouder extinguibbers were uned to ext innuisit fire p:ior to arrival of fire depar:r:ent n.
H.mes ucre rinted and the turbine L
.hu ild ing inside va l ~l. adjacent to the t r.in:;ferner, c:tr spray.'d :
for cooling.
~, o.-..
.y Enclo9ure 3 7.
Time Event 41449 All ve t fann secured, and turbine roof vents shut.
-1453 Firnt town fire units arrived 1455 Five fire units on site 1500 control Rod. Drive System secured to prevent reactor unter level from increasing further (s65" at this time).
i 1501
-Reactor Cleanup System uhich had isolated uns restarted and draining of reactor water started.
1507 Seven fire units on site.
1522 Normal station service was restored and diesels A and B were secuted.
j
'1527 Turbine turning gear uns engaged.
1530 The fire was declared officially out by fire departnent personnel.
1532 Manual initiation of relief valves to control reactor pressure (N1050 psi) and IcVel (>50")
1534 RCIC on line pumping CST to CST to reduce vessel-level.
4 1
{-
1555 MS1V's were opened after equalizing upstrean and dounstrean headers. These had isolated initially as a result of the loss
~ f the protection MG sets and remained' shut duc to high vessel o
i 1 cycl.
-J 1600 SJAE's restarted to continue a normal reactor cooldoun.
Reactor Recirculation pnmps were not restarted to prevent excessive thermal stress due to differential temperatures.
I-1639
.HSIV's ucre reopened after equalizing upstream and dounstrean headers. RCIC and SJAE's were restarted and a normal cool-down continued.
1648 MSIV's again isolated due to a transient'high vessel level caused by operator. partially opening one bypass valve to continuc the vessel cooldown. At this time further attempts to continue a normal cooldown using the main' condenser unre terminated.
11657 Torus cooling was establisi.d. to, repare for a nomal cooldown without the uain condenser.
t 3700 IlpCI t an n inoa3 Jy started and operated on minimua flou.
L A normj reac tor coolihn:n uit hout ' the main coadenser continued j
at 470*P/hr.
- "C O.
Shutdoun cooling van placed-into normaj ervice.
L1
t ;. ~ ~-
= ~ : :=.'.9 ~- - : ~ -
-~--
.,,'. q, t 03cd... :.. :./ ?:
J.
. r,
^
l
.--.h.. ; s.
- ~. i.
i g.--
e oo
,, t.
....3 o,- --.. - l 8
t..,
0l
.t. Ia
,x, E
o ao
,9-
-to
.I
- i
,:e.
l f...,s.A.,_ i s.,
.s 8
.;- /' t..E t l,, e
- i.,:...~... u....._. s..
p / _..._ 1,.3
,2 7,C. >y
- u. w-r.
v
,,t S
-k'
.s, g
c t.
m c
w 0.,
e
.2 c
j
$a
/-f
,.4
~~ g p. ;"
w i-G Q.a S J' t
/
v_M d)
.;g
- 7 +n @
d s.
)
.c g
m.
<p.m a, e
93 t>-
n3 U.
^
k-Q1 et) y4p.
4 n
e
- r.JA s
2 1f.
%~
Q
- l' A
2 u,
>4 -
N
/
.n a,.
a, n d'
-v.
c s
s y_
.n 2
e m
- g.,.
.t y
g e
4 g
/s
'j k
a,1
~
i,a 4
a 2%
u9 i
s s
La y
4.o 4
2
{ /\\ /\\
. y s
e m
.I L.
i t
m ii
.s rs
'N' S
-lg N
9) i t':.
4'-
4 4
A o
N n) 1p
'O
-.... 0) s.
og M
c--
..q
=
g, (s
'N s -,j Y
.1 i
r.y w.
I p
R-g,. --- -
s.s --
4 s :,
g ta q,.
c.
s
. 'I 4 W* * $'
p[%
5%. *
- c3 h
f-. l N's._. ___[, y w! b !,'
- J f.)/'O
.Y.
A.g8 j
\\s.,,,,. '/
(.
"a l '
I e
'd.
th s,y s
, 4) r.)
j
<,,k C ( ~i i.
^ "\\
n R.
s.
s ' '.
.t
,9 is
- -i
..l t
s.
(y 1s e,
s j.
Is -,.
m
- O
,e---- -.,-
.7
'9 r.
M.
c..
n.
N;,
irl
-3 s;
q. y j,,3... -._
<.n
,----..i.;)
a
.v f.,
._.3 l,.
n
,v; =
1 a
l
.j l_
~
c'.
I
...,._....'...'.'d'.vl*
l C
t., s I
f ry )
r' 1
f.]
..s.,
l c.
v r,
.1
.I3 c's t
N+
I aansopua I
a.s o,..
.