Three Mile Island, Unit 2, Revised of Accident Analysis, NSAC-80-1, March 28, 1979.

448 Pages·2012·20.28 MB·English

S 4, ', . .. . V,I
Analysis of Three Mile Island Unit 2 Accident
-
4NSAC-80-1 .
:
NSAC-1 RevisediM arch 1980
*1
Prepared by the
Nuclear Safety Analysis Center
Operated by the
Electric Power Research Institute
3412 HilMew Avenue
P.O. Box 10412
Palo Alto, California 94303
'''I
I, 8307050509 800331 '
PDR ADOCK 03000289 Az
P HOL
... .* .4,
100mapo.-Rommý
NUCLEAR SAFETY ANALYSIS CENTER
SEQUENCE OF EVENTS
TMZ 2 Accident - March 28, 1979
COMMENTARY
The intent of this sequence of events (SOE) prepared by the Nuclear Safety
Analysis Center (NSAC) staff is to present a factual account of the event
at the Three Mile Island, Unit 2, nuclear power plant on. March 28, 1979.
It is not meant to explain why the event occurred or to speculate 'on why,
certain actions were taken. This SOEEhas been verified, when possible, by
raw data such as computer output, reactimeter data, strip charts, ete.
Events have also been identified and verified by thermal hydraulic or core
analysis. EIn tries concerning radiation readings were the only ones which
p.
were not substantiated by raw data because of the una'vailability of
readable, reproduced or original, strip charts at NSAC. Limited use was
*" made of interviews by others with persons involved in the event. NSAC had
* no first-hand interviews with TMI-2 operators on duty at the time.
Commentary as to why certain actions were taken have been generally
' omitted, except. by inference. Certain actions may have been omitted if
they could not be confirmed, even though they have been reported by other
sources, as long as these actions did not appear to play an important role
in the event.
Appendices have been prepared to further explain the actions and remarks,
and to give a narrative description of the events from a thermal hydraulic
and core assessment viewpoint. System related appendices are not meant to
be independent system descriptions, but are written to clarify or amplify
remarks in the SOE.
In some cases, it has been difficult to interpret the available data and
the interpretation is still in progress. An example of this is the
interpretation of make up pumps status alarms and engineered safeguard
actuation status alarms.
WICLZAR SAFETY ANALYSIS COMR
SEQUqD4CZ OF EVENITS
TH! 2 Accident - March 28, 1979
Plant Status Prior to Start of Event
fUI Unit 2 a operating at 97% power with the Integrated aontrol system (ICS) in full automatic. The reactor coolant
system was o"erating with four1 reactor coolant ps at & pressure of 2155 p.1g. Roactor coolant makeup -9 Is wa in:
service providing normal makeup and reactor ooolant pump meal injectiou flow. Roactor coolant system letdown flow was
approximately 70 gpm. 2he reactor coolant system boron concentration was aproKimately 1030 parts per million. Red
groups oe through five were fully vithdrawn, rod groups six and sevem We"e 9 withdrawn and rod groupeight .was :27% '
withdrawn. Reactor coolant system leakage was a-.p proximately .,6 -.- h. mate system was operating vith two.
condensate pumps and two condensate booster pumps In service. both turbine driven. feed pump.. were in service. The
pressurizer spray valve and the pressurizer heaters were in manual control while spraying the pressurizer to equalize the-ý
boron concentrations between the pressurizer and the rest of the reactor coolant system. This eqialization WAs necessary
because of steam leakage past either the electromatic relief valve ar the pressurizer safety valves. This- leakage was
evidenced by periodic safety valve discharge header temperature alarms. ;
Operators were experiencing difficulties in transferring resins from an isolated condensate polisher to the receiving
tank. AttAmpts to free the plugged transfer line had bee.a in progress for about eleven hours.
TM Ounit I was in hot shutdown for low power physics testing following refueling. here was a vacuum on the c0nden0se and
al iliary steam ws being supplied from Wit 2.
2
TINE~~~7.i RDAK RN -
TIKE
-00O00:01 Condensate pump IA & 13 (Co-P-lA) tripped. Ref. 3.a., Appendix C/FV. p.3.
(0400:36)
START OT EVENT
I
OS00000 Feedvater pumps IA G M (lh-P-lA & f-P-Il) Ref. 3.a.e lore l(cid:127)se The trips werep caused by :low
(0400037) tripped.
feedvater pump suctIon pressurme s eewalter f low was
lost to both steian generators. 0
00:00:00 The main turbine tripped.. Ret. 3. .o The turbine tripresultsau
(0400:37)
from the trip of both feedvater: pumps.
00:00:00 Three emergency feedvater pump 1 2A a 23 Ref. 3.a. Automatic start of tbese pumps-isnaue
(0400:37) (SF-IP-i. I-P-2A& and 7r-P-28) started. -by the trip of both feed"ate pu - *" " "ergency
feedwater pump I (Wr-P-1) -Is a steam turbine driven
pump, and emergency feedvaet pump 2A 9.28 (EF-P-2h
and Xr-P-23) are electric noto driven pu~s I'
GOMM:003 The pressure setpoLnt (2255 paig) of electro- Ref. 1.k, S.b. The rate-ot-chanije of the reactor-
90400140) matic relief valve (ERV) (MC-2) located an the coolant system pressure Indicated that the relief -
pressurizer was exceeded. valve lifted.
A:4
3
J
TIMR
USV1110
TIEMAE~K~~ ama VRfE MENECES
00:00:04 Pressure began increasing in the reactor
I (0400:41) coolant drain tank. Ref. 1.J. This was another indication that the EIW
lifted. Reactor coolant drain tank pressure at this.
time was approximately 4 psig.
00:00:06
I Secondary side steam pressure reached 1074
I (0400:43) sptseimg ing ensteeraamto rg e3n.erator A and 1052 peig in cRheaf.r ts1 .uin, di1c.avt. ed Ptrheasstu sroems e fmroamin thstee armea cstaLfmeteyt ervalves
lifted.
00:00:08 2be reactor tripped on high reactor coolant
(0400:45) 2s3y5s5te mps ipgr.essure. The nominal trip setpointt is 2R7e.f . 3R.e*a, cto1rA k coo11l an- t S"eycst.t em2 .p2r-e1s. suArpep ernedaicxh eIdH , 23p4.4
WSg at 040z46, as indicated on the reactimetor.
ftb higher reading of approximately 2435 ptig
-
observed on the wide range reactor coolant system,.
-atripchart could he caused by a 50 to 60 peig higher''
rea"ding at the start of the event cpled with Pen
*overshoot during the rapid preasm.leIncrease.
! 00:00308 Pressurizer beater groups 1 through 5
(0400:45) Indicated off. Wef 3.a# 2.* -P. 2 . Appendlx, 1CSK -pp. 2-5.
*This event could signify the operator's-reported
action of placing the pressuri zer, beater control in
t.he automatic mode to mitigate expected -reactor
I ,coolant system pressure transients following any:.
reactor trip.
4
1 j
'I-
A
S -
RW,&W~ & RERFtEIICES
TIME
Ref. 1.k, 5.b. Appendixes EIV - p. 1, qPCS - pp. 3,
00:00:12 Reactor coolant system pressme decreased
6-7. The ERV should have reseated (closure setpoint
(0400:49) below the uetpoint value for WI'7 (PC-R2)
was 2205 psig), but it remained in the full open
closure.
position.
Ref.. A nmenmtaxr coolant insurge followed by a
00:00:12 Xndicated pressurizer coolant level peaked at -1.g.
rapid coolant outsurge is a nzrmal event. follovwin a
(0400%49) 256 in. and began a rapid decrease.
reactor trip.
Rae. 3.d, 2.d, -p. 1, 2.e ,p. 2l.Appeni DPI. -
00:00:12 Letdown flow was stopped. pp. 1. 3, 6. This step and the next are initial
(0400t49)
.actions for operators to take aft er' reactor trip.
accidents to compensate for the expected reduction
of pressurizer level.
Ref. 3.a., 3.d, 2..c p. 2, 2.d. -p. 2, Appendix
One or more attempts were made to start makeup
(0400&50) pump IA (MV-P-IA). The pump did not start. UPI -pp. 1, 6 , 7.
OOsOOMl
00:00:13 A condenser hotwell l(cid:127)w water level alarm was -Ref. 3.a, Appendices, C/FO[l - p. 5, PDS pp.- 12 -
13. The level was 21.72 in. Because of the 15
(0400:50) ivceld on the alarm typewriter. (Noninal
second scan interval of this-parameter, the actual
alarm setpoint was 22.5 in.)
alarm many have been aecived before this time.2
S
TIME EVENT TIMEE VDFWa tARMEFKE RENCES
00:00014 The emergency feedwater pmpe (EF-PI, EF-P-2A, Ref. 3.a, Appendix PDS - pp. 12-13.
(0400:51) and EF-P-28) low pressure alarms cleared on F-P1 1237 psig
I the alarm typevriter. EF-P2-A 1471 psig
EF-P2-B .1445 psig
secause of the 15 second scan interval of these
parameters, these pressures were probably reached
before the time printed out.
2~.
00:00014 Pressurizer hbater goupe I through 5 indicated Ref. 3.a, 2.e -p. 2, Appendix RPCS- pp.- 2. 3-5.
S.
(0400s51) on. A low reactor coolant system pressure with the-
beater control in automatic would came the beaters
to energize.
OOsOOS steam generator A water level indicated 74 in. Ref. 1.q,A .x, Appendix otsG - pp. 2-3.' Steam
(0400M52) on the startup range. Steam generator 3 water generator water levels vere decreasing,
4,
level indicated 76 in. on the startup range.
S00tOslS The pressurizer spray valve (RC-V1) closed). WOf. 1.1, 2.e -p. 2, Appendix NPC p.- 5,-6. ?
(0400:52) This clsure Indicated that the spray valve was
I
responding normally to reactor coolant system
pressure transients and supports the operator' s;,- .-
reported action of placing the pressuriser spray in" -
automatic.-
6
- -- r~>.W-. --- - --
4 ,~-(cid:127) -i¸-(cid:127)
TIME
EVENT
REMARKS & REERENCZS
00:00s28 The condenser hotwell low water level alarm
(0401,07) cleared. (Nominal alarm setpoint was 22.5 Ref. 3.a. Appendix C/roW - p. 5. The level was
in.) 26.44 in. The computer scan interval wan 15 sec.
00:00:30
The ZW (PC-32) and pressurizer safety valve
(0401:07) Ref. 3.c, Appendix ERV - pp. 3-4.
(DtC-RID) outlet temperatures alarmed high.
RC-R2 292.26F
DC-RIB 203.507
. - -
RC-RtI outlet temperature had b',u operating close
to Its high alarm setpoint prior to the reactor
trip. Computer scan Interval wa8 .30 sec.*-
00:00:30 The reactor coolant system low pressure trip
(0401s07) setpoint vas reached. Rtef. I.q, 5.b, Appendices CV=G pp. 2-4, IVDS.
p.2. •ergency teedwater valves Ell-VA - Er-V11W..
should open when levels reach 30 inches. Feedwater
vwa not admited to the steam generators. ZR ergency.
teedwater block'vlven Er-V 12A and.XF-V1231, which
.1
should have been 'open, vere closed. This fact was':'..
not recognized by the operators, at this time.
00200S33 Steam generator B water level decreased to
(0401s10) 28.0 in. in the startup range. Ref. U.x, 5.b, Appendices OaTG -- pp. 2-3, OS-
p.2. .See entry at 0401:07 ..
000t0O41 Makeup I 1A (NP-P-IA) was started.
(0401:18) Ret. 3.a, 1.g. With makeup pumps 1A a 15 operating,
the pressurizer level rate of, decrease slowed.
7
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I
TIME
TIENVEN T
FENARKS REY RENCES
O0000t46
Pressurizer
coolant reached an indicated
(0401s25)
I miniwim level of 158 in. Ref. 1,.g. Indicated presusiizer ooolant level began
to increase.
0000158
A pressurizer low coolant level alarm was
(0401035)
received. (nominal alarm setpoint Was " Ref. 3.a, Appendix P?3 - pp. 2, 15. 12-13. Because
200 in.) of the scan intervals and computation involved with
pressurizer coolant level, ttie alarm typewriter
00:01100 entry lagged the actual pressrizer low level.
Preasurtzer
(0401t37) sakety valMI (W-RUA) outlet
temperature alarned high. Ref. 3.a. Appendix C p-p. 3, 5-6.
JW-RIA
29415.
00*01t13
(0401T50) Are cceoinvdeedn. ser (Nhoomtwinealll ahliagrhm wgaetetpr olieavt ewl asa la3r6m i nw.)as Ref. 3.5. 2.C -p. 3. 2., p. 2, Appendix C/N - p.
5. Indicated levl was 37.77 in* The computer scan
Interval was IS see*
00,01#26
(0402:03) The Indicated reactor coolant drain tank
liquid tsmperature was S5.Se?. Ref. 3... This alarm typewriter entry indicated
that the reactor coolant drain tank liquid returned
to a normal temperature range. secause of the heat
addition to the tank at this tUim Ii I* probable
that It was a low temperature alarm that had
cleared.
I
a
I
I
*1
TIME rEv~r TIMErmREM6 ARRrKESN OCE
80:01:45 Ib steam generalu boiled dry on the Urf. l.b, 1.c, i.4. I.e. 1.u, I.v. ITS ev-t WA
10402:22) seomndary side. indicated by a steodily decreasing tm 90enerator
Approximate sndary side pressure while reacum coolant hot
and cold leo temperatures were i ung Zf~C-
tiw beat transfer from the primary coolant to the
I
secondary system is stopped when the sm gemm-
&taow are dry.
I
M*02:01 osgimmered safety 0 for highI psure .ef. 3.&, 2.c- p. 2, 2.0 - p. 4. In11S ee. 3.3.2.-1.
96402:38) Samjectiom actuated-. Bppemdces 35 - pp. 6. 7, 9, UPI -- pS. 9 . Tbis s
caia by reactor cooant rystem a re droupftg
bello 1640 pui,.
SZ
-wam pum In 3iWU tripped. let. 3.a. 2.q - p. 2. appendix 3W - wp. 14-15.
Tbis is an autmatic trip before bi* pressure
injectio pumps SA a IC (MU-P-IA and m-P-1C) start.
3tr-gh
vmS pressure injectiem pamp IC (KU-P--iC)
started automatic&il1'. Vat. 3.a, 2.9 - p- 2, Appendices W - pp. 9. 14.
"IP -- P. 9. Po IA (IU-P-IA) was already
operating.
9