ML19263E817
| ML19263E817 | |
| Person / Time | |
|---|---|
| Site: | Oyster Creek |
| Issue date: | 05/17/1979 |
| From: | Nowicki S Office of Nuclear Reactor Regulation |
| To: | Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 7906250320 | |
| Download: ML19263E817 (23) | |
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'o UNITED STATES e
E j ),, c [,j NUCLEAR REGULATORY COMMISSION
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May 17,1979 C
WASHINGTON, D. C. 20555 k,
Docket No. 50-219 LICENSEE: Jersey Central Power f. Light Company FACILITY: Oyster Creek Nuclear Generating Station
SUBJECT:
Summary of May 9,1979 Meeting Concerning the Low Low Low Water Level Alarm Experienced at Oyster Creek On May 9,1979, the NRC staff met with' representatives of Jersey Central Power &
Light Company (JCP&LCo) and their consultants. The purpose of the meeting was to resolve our concerns regarding the events of May 2,1979, that resulted in the water level in the Oyster Creek reactor vessel decreasing below the Low Low Low Limit. Copies of the attendance list and meeting agenda are provided as Attachments 1 and ?.
JCP&LCo presented a system description, sequence of events, results of the analyses of the event, a brief discussior, of the safety limit, and the status of the Oyster Creek Plant. The viewgraphs used in the presentation are included in Attachment
- 3.
An extensive question period followed the licensee's presentation to allow the NRC staff to better understand the event and to resolve their questions concerning the event and its generic implications. The staff agreed to provide the licensee with written questions that requira a written response before the Oyster Creek Plant would be allowed to return to operation.
A brief summary of some of the key items discussed at the meeting is given below:
1.
Initiating Signal The initiating signal that caused the scram was introduced by a technician in a 1/4 inch pressure sensing line that contained the reactor scram and recirculation pump pressure switches.
2.
Initiating Event Recorder The event recorder was not designed as a " sequence of events" recorder but as an " initiating event" recorder. Therefore, by design, the recorder automatically begins to run a high speed upon receiving an initiating signal. A timer automatically returns the recorder to slow speed three 2214 020 7906250 3E0
. minutes after the initiating signal. The recorder can be turned off by opening the cover to read the chart paper or by switching to off. The recorder was turned off three minutes after the scram, but the licensee does not know if it was off because someone was examining the chart or the switch was turned to off. The licensee is considering replacing the initiating event recorder with a sequence of events recorder.
3.
Analysis of Minimum Water Level The analysis performed by General Electric Company and Exxon Nuclear concluded that the minimum collapsed water level (i.e., no voids) was:
a.
using the Exxon boil off method 41 foot above the top of the core b.
using the Exxon mass energy balance method % 2 feet above the top of the core c.
using the General Electric Company boil off method % 16 inches above the top of the core The licensee has concluded that the core was not uncovered during the tvent.
4.
Empirical Evaluation Analysis of the primary coolant, the off-gas monitors and the process instrumentation shows that no increase in radioactivity resulted from the transient. The licensee has concluded that no fuel damage has occurred as a result of this transient.
5.
Follow Up Action The licensee is conducting or has performed control rod scram tests, control rod motion tests, analysis of reactor water activity and analysis of the off-gas system samples to further confirm that no fuel damage resulted from the transient. The licensee has revised operating procedures to assure that the operator will take proper action during the course of a similar transient and appropriate operator training is being conducted.
Plastic covers have been installed on the recirculation pump suction and discharge valve switches to discourage the operators from moving these valve positions without giving thought to his action. The licensee is considering replacing the initiating event recorder with a sequence of events recorder to aid in analyzing transients when they occur. The licensee is reviewing plant procedures to detemine if procedure changes should be made to prohibit system su/veillance during operation when a startup transfomer is out of service.
2214 021
. 6.
Licensee's Conclusions The licensee had concluded that the core was not uncovered and no loss of fuel integrity resulted from the transient. The licensee is treating the event as if a safety limit had been violated and therefore will not return the facility to operation until receiving Comission approval. All mechanical work (e.g., installing the plastic covers) has been completed and after May 10,1979, the facility will be ready to resume operation as soon as all the analyses have been completed and startup approved by the NRC.
A final expanded version of the sequence of events during the May 2,1979 transient was given to the Comission and the news media at the conclusion cf the meeting. This document is provided as Attachment #4.
At the conclusion of the meeting the licensee was requested to submit (1) a detailed report of the incident including answers to our questions and (2) a request for Comission approval to resume operations. We agreed to provide our written questions to the licensee in one or two days.
571 4 s/M Stanley J.
wicki, Project Manager Operating Reactors Branch #2 Division of Operating Reactors Attachments:
1.
Attendance List 2.
Meeting Agenda 3.
Viewgraphs 4.
Sequence of Events cc w/ attachments:
See next page 2214 022
. cc w/ attachments:
Mr. I. R. Finfrock, Jr.
Vice President - Generation Jersey Central Power & Light Company Madison Avenue at Punch Bowl Road Morristown, New Jersey 07960 G. F. Trowbridge, Esquire Shaw, Pittman, Potts and Trowbridge 1800 M Strect. N. W.
Washington, D. C.
20036 GPU Service Corporation ATTN:
Mr. E. G. Wallace Licensing Manager 260 Cherry Hill Road Parsipaany, New Jersey 07054 AntN ay Z. Roisman Natural Resources Defense Council 917 15th Street, N. W.
Washington, D. C.
20005 Steven P. Russo, Esquire 248 Washington Street P. O. Box 1060 Toms River, New Jersey 08753 Joseph W. Ferraro, Jr., Esquire Deputy Attorney General State of New Jersey Department of Law and Public Safety 1100 Raymond Boulevard Newark, New Jersey 07012 Ocean County Library Brick Township Branch 401 Charbers Bridge Road Brick Town, New Jersey 08723 22)4 023 ATTENDANCE LIST MAY 9,1979 Jersey Central Power & Light Company Scandpower, Inc.
S. Laird D. Pomeroy J. Sullivan J. Carroll, Jr.
Exxon Nuclear Company D. Ross I. Finfrock, Jr.
C. Leach T. Crimmins K. Galbraith T. Tipton J. Knubel GPU Service Corporation K. Fickeissen J. Pelrine G. Bond E. Roessler R. Wolf Niagara Mohawk NRC C. Mangan S. Nowicki General Electric J. Kaight H. Vander-Molen J. Wuedford E. Jordan L. Youngborg D. Ziemann J. Duncan R. Campbell J. Kilty P. Check F. Coffman States News Service R. Woods C. Berlinger R. Gettiin M. Mendonca W. Hodges Asbury Parx Press, N. J.
W. Paulson E. Greenman S. Kent
- 0. Havens, Jr.
W. Morris R. Emch M. Chiramal P. Polk P. DiBenedettc D. Eisenhut T. Ippolito S. Rubin 221 4 024 OYSTER CREEK NUCLEAR GENERATING STATION SHUTDOWN AGENDA MAY 9,1979 10:30 Introduction Stan Nowicki Purpose of Meeting -
Meeting Conduct 10:45 Licensee Presentation Introduction Don Ross Systems Description Jim Knubel Sequence of Events Joe Carroll Supporting Analyses Gordon Bond Safety Limit Not Exceeded Don Ross Followup Actions Taken John Sullivan Startup Schedule Don Ross 12:15 Break 1:00 Questions 3:15 Summary 4:00 Adjourn 2214 025
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SEQUENCE OF EVENTS TIME (SEC.)
EVENT 0
REACTOR SCRAM /RECIRC. PUMP TRIP 13 TURBINE TRIP / LOSS OF FEEDWATER/ CONDENSATE PUMPS 13.6 LOW WATER LEVEL SCRAM POINT 16.8
- 2 RPS MOTOR GEN. SET TRIP 31
- 2 DIESEL GENERATOR BRL..<ER CLOSED 43 MSIV CLOSED 76 B 150. CONDENSER IN SERVICE 90 LOW WATER LEVEL ALARM CLEARED 172 LOW LOW LOW WATER LEVEL TRIP POINT 186 RECIRC. LOOP DISCHARGE VALVES CLOSED 1914 C RECIRC. PUMP STARTED 2208 FEEDWATER PUMP STARTED 2340 RECIRC. PUMP STARTED 2700 RPS #2 RESTARTED / SCRAM RESET 3600 BANK 6 RETURNED TO SERVICE 22.14 030
SEQUENCE OF EVENTS RELATED TO SCRAM OF MAY 2, 1979, AT OYSTER CREEK NUCLEAR GENERATING STATION INITIATING EVENT:
On May 2,1979, at 1350 hours0.0156 days <br />0.375 hours <br />0.00223 weeks <br />5.13675e-4 months <br />, an inadvertent reactor high pressure scram occurred during required surveillance testing on the isolation condenser high pressure initiation switches.
Two (2) sensors (RE-03A System I and RE-03B System II) (see Figure 1) of the four reactor high pressure scram sensors share a common sensing line with the isolation condenser high pressure initiation switches being tested.
The technician performing the test was in the process of verifying that the sensing line excess flow check valve V-130-1 was open when the scre.m occurred.
The scram has been attributed to a momentary simultaneous operation of switches RE-03A and RE-03B due tr> a hydraulic disturbance associated with valve manipulations required by procedure to verify the position of the excess flow check valve.. The hydraulic disturbance also caused a momentary trip of the isolation condenser initiation switches (REISA and RE15B). These sensors were not closed long enough to initiate an automatic initiation of the isolation condensers, since a time delay is involved in the initiation logic. However, these sensors also are used in the automatic recirculation pump trip logic which did operate in tripping the four operating recirculating pumps.
No automatic time delay is involved in this logic.
INITIAL CONDITIONS:
Plant Parameters at the Time of the Scram:
Reactor Power 1895 MWt Reactor Water Level 79" Yarway (13'-4" Above the top of the active fuel)
(See Figure 2 for water level reference tabulation) 6.4' GEMAC 7214 031
Page 2 Reactor Pressure 1020 psig Feedwater Flow 7.1 x 106 lbm/hr Recirculation Flow 14.8 x 104 gpm Eouiement Out Of Service:
Relevent to Event Secuence:
A.
One of the two (2) startup transformers, SB(Bank 6), was out of service as permitted by Technical Specifications, to perform an inspection of its associated 4160 Volt cabling.
SB suppit :s offsite power to one half of the station electri. cal distribution system (see Figure 3) when power is not available through the station auxiliary transformer. The'4160 Volt busses which receive power from SB are 18 and 1D.
Buss ID supplies power to certain redundant safety systems.
Buss 10 is designed to be powered from #2 Diesel Generator in the event power is not available from either the auxiliary transformer or startup transformer.
Buss 18 supplies 4160 Volt power to non-safety related systems and hence, does not have a diesel backup power source.
B.
One of the five (5) recirculation loops (D) was not in service due to a faulty seal cooler, cooling coil.
The pump suction valve was open, the discharge valve was closed, and the discharge valve bypass valve was open.
No other systems and/or components important to the event sequence were out of service.
EVENT SEOUENCE: (To = 1350)
TIME OF EVENT (Sec)
EVENT DESCRIPTION 0
A reactor scram occurred for the reason previously described coupled with a simultaneous automatic trip of the four operating Recirculation Pumps.
The Control 2214 032
Page 3 TIME OF EVENT (cont)
EVENT DESCRIPTION (cont)
Room operator verified that all control rods inserted and proceeded to drive-in the IRM and SRM Nuclear Instrumentation. At this time, 4160 Volt power was being supplied from the auxiliary transfomer during the coastdown of the Turbine Generating System and the Feedwater System was in operation. Recirculation flow started decreasing due to pump coastdown. Steam flow started decreasing due to loss of heat production (scram) but feed flow remained at the full power flow rate.
Reactor vessel pressure decreased to the pressure regulator setpoint as steam flow decreased. Reactor water level bega. decreasing due to steam void collapse in the core.
13 The Turbine Generator tripped at the no load trip point which initiates an automatic transfer of power to the startup transformers.
power to Busses lA and 1C successfully transferred from the auxiliary trans-former to the SA (Bank 5) startup transformer.
Since SB (Bank 6) was out of service at this time, power was lost to Busses 1B and 10. As designed, Busses 1B and 10 separated through operation of breaker 10 and a fast start of Diesel Generator No. 2 occurred to power emergency loads o.' Buss 1D.
2214 033
Page 4 TIME OF EVENT (cont)
EVEliT DESCRIPTION (cont)
Loss of power to Buss 1B resulted in loss of Feedwater Pumps B and C and Condensate Pumps B and C.
Although power was available to the A condensate and feedwater pumps, via Bus lA, the A Feedwate.r Pump tripped on low suction pressure. Since water inventory was leaving the Reactor Vessel through the Steam Bypass Valves to the Main Condensers and a high capacity source of high pressure makeup water was not available, reactor water level and pressure decreased.
In addition, the loss of power to Buss 1B caused the B Cleanup System Recirculation Pump to trip which, in turn, caused an isolation of the Cleanup System due to low flew through the cleanup filter.
Furthermore, one condensate transfer pump and the operating fuel pool cooling pump tripped. An unsuccessful attempt was made to restart the A feedwater pump.
(The reasons for the restart failure are described later.)
(Event Reccrder) 13.6 Reactor water level decreased to the Low level scram setpoint which is 11'5" above the top of the active fuel region.
(EventRecorder) 16.8 The output breaker on the No. 2 Reactor Protection System M.G. Set tripped due to loss of power to the drive motor.
The cutput voltage f2d}tde hd4 Set had
Page 5 TIME OF EVENT (cont)
EVENT DESCRIPTION (cont) been maintained by flywheel action since the time of the turbine trip.
Power to the M.G. Set drive motor is fed indirectly through Buss 1D which was deenergized at this time.
25 The No. 2 Diesel Generator Breaker closed and supplied power to the 1D Bus. A second control rod drive pump started.
43 Reactor water inventory continued to decrease due to steam flow to the main condenser.
In anticipation of a Low Low Reactor Water Level automatic isolation of the reactor (which occurs at 7'2" above the top of the active fuel region), a manual reactor isolation was initiated to conserve inventory by closing the Main Steam Isolation Valves.
This action was taken at an indicated water level of approximately 30" on the Yarway instrument which corresponds to 9'8" above the top of the active fuel region.
It should be noted that the decrease in indicated water level and pressure was amplified by the effects of introducing cold feedwater into the vessel during the 13 second period prior to the Turbine Generator Trip.
The cold feedwater reduced the steam voiding inside the vessel thereby causing a shrink in water level.
2214 035
Page 6 TIME OF EVENT (cont)
EVENT DESCRIPTION (cont) 49 The Main Steam Isolation Valves fully closed, thus stopping the loss of water inventory from the vessel the.isy causing an increase in reactor steam pressure.
Indicated reactor water level started to increase shortly after isolation, when reactor decay heat re-established a steam void distribution.
(Event Recorder) 59.6 The reactor mode switch was transferred fr'm RUN to REFUEL.
76 (1 min. 16 sec.)
To establish a sink for the removal of decay heat from the reactor, the B isolation condenser was placed into service. At this time, the Control Room operator closed the A and E recirculation loop discharge valves (these valves take approximately two (2) minutes to close).
It is postulated that et this time, both B and C loop discharge valves were also closed. The conclusion that the five recirculation pump discharge valves were closed is based upon loop temperature response later in the event and is further supported 1
by the Low Low Low level at 172 seconds. The D loop was isolated previously.
(See the equipment out of service section).
(EventRecorder) 90 (1 min. 30 sec.)
The mctor low water level alarm cleared due to the water added from the isolation condens721to Primary System.
Page 7 TIME OF EVENT (cont)
EVENT DESCRIPTION (cont) 96 (1 min. 36 sec.)
The B isolation cendenser initiatien valve fully opened after 20 seconds. The temperature of the E recirculaticn loop, which srrves as the B isolation condenser water return path, decreased due to the effects of cold water from the isolation condenser.
The D recirculation loop temperature did not change appreciably.
A, B, and C recirculation loop temperatures increased slightly.
The heat-up is attributed to natural circulation through the cartially open discharge valves carrying het water (536*F) warming the lines previously cooled by the effects of cold feedwater.
The reduced flow area between the lower downcemer and lower plenum area, due to the slow closure of the discharge valves, started to cause a shift in water inventory frem the ccre area to the upper and lower downcomer region. The shift was due to the isolation condenser returning cendensed steam from the core area to the downcomers.
The water inventory shift continued as the discharge valves moved to the full closed position.
(EventRecorder) 172 (2 min. 52 sec.)
The reactor Low Low Low weter level instrument trip last recorded point on the event recorder.
point was reached.
This was probably caused by the voided mixture in the separators having drairad to the upper plenum, causing a reduction of static head above the Low Low Lcw water level instrument. This does not 2214 037
Page 8 TIME OF EVENT (cont)
EVENT DESCRIPTION (cont) nacessaril', i w: 'n inventory loss from the core but ra. ace a.adi.tribution of water and steam voids above t"
$te.
186 sec. (3 min 6 sec)
All recirculation loop discharge valves fully closed.
At this time, based upon closure initiation, the cooldown of the E recirculation loop stopped and a heat-up began. The indicated reactor water level increased due to the shift in water inven, tory.
Recirculation 1 cops A, B, and C continued to, heat up.
The mechanism of the heat up was due to heat transfer between the hot recirculation loop piping and the water in the piping.
Reactor pressure continued to decrease as a result of isolation condenser operation.
250 (4 min 10 sec)
B isolation condenser was removed from service to reduce the rate of cooldown of the Primary System.
Removal of the condenser caused indicated water level to decrease.
The decrease in indicated water level was due to a return of water to the core region from the downcomer region through the five (5), two-inch (2")
bypass valves around the recirculation loop discharge valves.
During this period, the net water inventory effect was a storege of water in the recently secured isolation condenser.
Thc recirculation loop discharge temperatures reached equilibrium and followed a slow cooldown trend.
2214 033
Page 9 TIME OF EVENT (cont)
EVENT DESCRIPTION (cont) 270 (4 min 30 see)
The reactor pressure increased due to the effects of removing B isolation coridenser. The rate cf decreese in water level sh'ifted from a ramp of approximately 37 in/ min to 2 in/ min. The reason for this change is the isolation condenser tube assembly was completely filled.
The flow through the five (5) 2" bypass valves continued, accounting for the change in scope.
450 (7 min 30 sec)
Both isclation condensers were placed in, service.
This caused an increase in indicated water level and a decrease in pressure.
The A recirculation. loop tempera-ture decreased because cold water from the A isolation condenser entered the.A recirculation loop which is its return path to the reactor. A portion of the water passed through the loop via its 2" bypass valve, thus causing the cooldown.
528 (8 m1n 48 sec)
To slow the rate of cooldown, the B isolation condenser was removed frem service. At this time, the indicated water level reached a maximum of approximately 14.4 feet above the top of the active fuel (88" on Yarway).
This is considered to be above normal water level for full power operation.
When the B isolation condenser was removed from service, indicated water level decreased to 13'8" above the top of the active fuel where it remained until approximately 1212 seconds when A 721a n39
Page 10 TIME OF EVENT (cont)
EVENT DESCRIPTION (cont) isolation condenser was removed from service. The
' reactor pressure continued to decrease and all recir-
^
culation loop tem'peratures continued to trend downward.
Indicated water level was stable at this time because the head of water in the downcomer region was sufficient to establish equilibrium between the water entering the core region via the 5 two inch bypass valves and the condensed steam returning to the downcomer from the isolation condensers.
540 (approx) (9 min)
The four (4) Low Low Low water level indicators were verified locally to be below their alarm setpoint which is 10".
The reading appeared to be at or below the instrument's lower level of detection.
810 (approx) (13 min A recheck of the triple Low Low Low water level indicators 30 sec) showed that the pointers were active (moving) although they continued to read below their alarm point. The instrument was at or slightly above its lower level of detection.
1212 (20 min 12 sac)
A isolation condenser wa cemoved from service, thus stopping the removal of inventory from the core region.
Indicated water level decreased as the water in the downcomer region flowed into the core region.
Reactor pressure started to increase due to the decay heat steam production.
2214 040
Page 11 TIME OF EVENT (cent)
EVENT DESCRIiq iod (cont) 1488 (24 min 48 sec)
The isolation condensers were used several more times to control the reactor cooldown with predictable increases in indicated water level and reduction in pressure. This mede of operation continued until 1914 seconds.
1914 (31 min 54 sec)
In order to more correctly determine the plant ccoldown rate C recirculation pump was started.
It was noted that ;he indicated water level dropped apprcximately 3 feet in less than two minutes. The C recirculation pump was shutdown and isolated to investigate the reason for the drcp in level.
In response to the indicated water level drop, a second attempt was made to start the A feedwater pump.
Since water level appeared to be satisfactory pr'or to this time based upon control rocm water level indicators, no attempts other than the initial attempt at 13 seconds were made to start the A feedwater pump. The pump failed to start due to a tripped overload on the auxiliary oil pump which is interlocked in the pump starting seq-
.e.
The indicated water icvel started to increase due to the action of the operating isolation condenser tr'ns-ferring water to the downcomer region.
When the C recirculation loop was started the loop temperature increased from approximately 400 F to 470*F.
The other recirculatica loop temperatures continued to trend down.
At this time Low Low Low alarm may have cleared.
2214 041
Page 12 TIME OF EVENT (cont)
EVENT DESCRIPTION (cont) 2208 (36 min 48 sec)
The A Feedwater. pump was successfully started by locally starting the auxiliary oil pump which satisfied the required starting interlocks.
Indicated water level increased to a level correspc-ding to 13'8" above the top of the active fuel region.
Realization occurred that the indicated water level and core water level may not have been the same when it was recognized that the five recirculation loop discharge valves were closed.
2340 (39 min 0 sec)
The A recirculation pump was placed in service at a flow rate of approximately 1.9 x 104 gpm, thus removing the disparity between water level measuring systems.
The Low Low Low water level alarms were known to be cleared at this time.
Indicated water level dropped approximately three feet to 11'4" above the top of the active fuel.
The A recirculation loop temperature rose from 375'F to 465*F when it was placed in service.
Steps were initiated at this time to bring the plant to " cold shutdown condition".
2700 (45 min 0 sec)
Reactor Protection System #2 restored and scram reset.
3600 (1 hr.)
The SB transformer was returned to service and Buss 1B was energized.
2214 042