ML20090D400
| ML20090D400 | |
| Person / Time | |
|---|---|
| Site: | Nine Mile Point  |
| Issue date: | 08/01/1973 |
| From: | Burt P NIAGARA MOHAWK POWER CORP. |
| To: | Skovholt D US ATOMIC ENERGY COMMISSION (AEC) |
| Shared Package | |
| ML20090D404 | List: |
| References | |
| 6075, NUDOCS 8302280114 | |
| Download: ML20090D400 (2) | |
Text
7 C
O NIAGARA MOHAWK POWER CORPORATION NI AGAR A MOHAWK Nine Mile Point Nuclear Station Post Office Box 32 Lycoming, New York 13093 August 1, 1973 h
Mr. Donald J. Skovholt e
Assistant Director for Reactor Operations g[
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Division of Reactor Licensing pf' NI. 4, > r ;) Ny' O
United States Atomic Energy Commission Washington, D. C.
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Dear Mr. Skovholt:
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Re:
Provisional Operating License:
DPR-17 g 7 7, p /',, > '
Docket No.:
50-220 NLc.
The following is a report relating to the operation of Nine Mile Point Nuclear Station Unit # 1 in which during routine surveillance testing of main steam isolation valves, a reactor scram occurred.
On July 8, 1973 at 0552 hours0.00639 days <br />0.153 hours <br />9.126984e-4 weeks <br />2.10036e-4 months <br />, Nine Mile Point Unit #1 experienced a reactor scram while operating at 560 MW and 1740 MW. The scram occurred during surveillance e
t testing of the main steam line isolation valves.
All systems operated as designed following the scram and no safety limits were exceeded.
Subsequent investigation showed that the scram resulted from the isolation of #12 main steam line, which caused an increase in reactor pressure which in turn resulted in a high neutron flux scram.
The isolation of No. 12 main steam line was caused by the closing of the outside isolation valve in that line during the surveillance test.
Reactor pressure increased from a value of 1012 psig at the time of the scram to a peak value of 1091 psig, 12 seconds after the scram.
This pressure increase occurred when high steam flow in the No. 11 steam line caused main steam line isolation. The high steam flow signal was caused because all of the steam being produced was being forced into one steam line at this time. The steam line isolation occurred approxi-mately 7 seconds after the reactor scram.
The electromatic valves and isolation condensers operated during the transient to relieve reactor pressure.
Information pertaining to these operations is limited due to the nature of the data logging program in the process conputer.
The program is initiated by any half scram and runs for 5 seconds.
It then is interrupted for approximately 2 minutes to allow data collection for the Post :lorten Recall program.
It was during this tine that the turbine trip occurred, electromatic valves and isolation condensers operated. Hence, the exact times of operation were not recorded.
However, by observing the reactor pressure at one second intervals on the Post Mortem Recall print out, it was determined that the electromatic valves and isolation condensers did operate.
The Post Morten Recall data indicates that the relief valves operated when the reactor pressure reached 1091 psig at 12 seconds after the scram.
During the next 6 seconds, reactor pressure decreased from 1091 psig to 1067 psig while steam flow to the torus increased from 406 k Ib/hr. to 1022 k Ib/hr. and then decreased to 638 k Ib/hr.
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this time, reactor pressure again started to increase and again reached 1091 psig at 21 seconds after the scram.
Once again the relief valves operated to relieve pressure.
Steam flow to the torus increased from 210 k Ib/hr. to 1086 k lb/hr. and then decreased to 575 k lb/hr. 27 seconds after the trip.
Reactor pressure decreased to 1069 psig.
At this point, reactor pressure again started to increase but did not go high enough to actuate relief valve operation.
Instead the isolation condensers controlled pressure.
The reactor pressure increased to 1086 psig at 32 seconds after the scram and then began to decrease on a steady downward ramp.
During the transient the feedwater control system provided adequate automatic control limiting reactor water level to -3.20 ft. 13 seconds after the scram and recovering to
+1.08 ft. 37 seconds after the scram.
Immediately following the transient, members of the Nine Mile Point supervisory staff analyzed the transient and observed many operations of all four main steam line isolation valves in an attempt to determine if the valve controls had malfunctioned.
All valves operated properly.
At this time, the staff members agreed that no safety limits had been exceeded and that a reactor startup could commence.
On July 9,1973 the onsite review committee held a special meeting for the purpose of reviewing this transient. The control room operator was also interviewed by the committee.
The closure of a main steam isolation valves are a requirement for the safety analysis.
To insure valve operability, a surveillance test is conducted twice weekly. Although the valve closed during a test, it assumed the proper position to preserve the health and safety of the general public.
The committee reached the following conclusions:
a.
The reactor scram resulted from high neutron flux due to a pressure transient which occurred when #12 main steam line isolated.
1 b.
Number 12 main steam line isolation was caused by the closure of a main steam isolation valve during surveillance testing.
l c.
The committee agreed that no safety limits had been exceeded and that all systems operated as designed.
There was no threat to the health and safety of the general i
public during or following the transient.
l Very truly yours, 1
MiO P. Allister Burt General Superintendent Nuclear Generation j
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