ML20084G961
| ML20084G961 | |
| Person / Time | |
|---|---|
| Site: | Oyster Creek |
| Issue date: | 01/25/1972 |
| From: | Finfrock I JERSEY CENTRAL POWER & LIGHT CO. |
| To: | Morris P US ATOMIC ENERGY COMMISSION (AEC) |
| Shared Package | |
| ML20084G962 | List: |
| References | |
| NUDOCS 8304270189 | |
| Download: ML20084G961 (2) | |
Text
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Jersey Central Poweg & Light Company
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M ADISoN AVENUE AT PUNCH BOWL Ro AD e Mo R RIST oW N, N. J. 07960 e 539 - 6111 January 25, 1972
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gNw Dr. Peter A. Morris, Director T
Division of Reactor Licensing 17 st United States Atomic Energy Commission N
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Washington D.C. 20545 g
Dear Dr. Morris:
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Subject:
Oyster Creek Station Docket No. 50-219 Control Rods Latching at Position 02 gi This will advise that two control rods (18-11 and 30-31) latched at position 02, six inches short of fully inserted position 00, when the reactor was manually tripped on November 16, 1971 in connection with an incident that involved the loss of the station air system. This incident was reported to you in my letter of December 17, 1971.
This phenomenon had been experienced previously and is attributed to increased leakage past the stop piston seals in the control rod drive mechanism. Buffer orifices ~,~ comprised of a series of graduated holes, H lov vater to flow from the D.rea above the drive piston during a scram or normal rod insertion.
During a scram, the rapid insertion of the drive piston closes off the larger of these
. orifices causing water to be trapped between the top of the drive piston and the bottom of the stop piston. This water is forced out of the smaller orifices in the piston tube thereby creating a buffer action to decrease the rate of travel of the drive piston as its upward travel closes off orifices one at a time. Due to increased leakage of reactor water past the stop piston seals into ftheventedregionabovethedrivepiston,thefinalorifice(1/16-g] p - t hr.
, inch hole) cannot pass enough water and the control rod decelerates and stops slightly below the 00 latch position.
The drive then k-settles back into the next, or 02, latch position.
Station procedures require the reactor operator to verify that all control h 5 j/
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rods are fully inserted following a reactor scram.
Under these g,9f) circumstances, and also in accordance with procedures, the control J
k rods were promptly inserted to the 00 position by manual operator S///
action.
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8304270189 720125 POR ADOCK 05000219 M30
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S PDR COPY SENi' RE3 ION b
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O Dr. Peter A. Morris Page II January 25, 1972 Our continuing program of control rod drive system sur-veillance includes the monitoring of scram time for 26 selected drives, monthly stall flow measurements, weekly exercising of all partially or fully withdrawn control rods, and the observation of control rod performance during the day-to-day control rod move-ments associated with power operation. The results of this surveillance program indicate normal control rod drive system performance.' As previously reported to you in my letter of May 18, 1970, the reactivity worth of a control rod is very small between the "02" and "00" position, with the total worth of all 137 control rods between these two notches being only approximately 0.50% AK.
This may be compared to a value of keer of approximately 0 95 under cold shutdown conditions with all control rods fully inserted.
In view of the foregoing, we conclude that the control rod drive system. continues to.be capable of performing its intended function.
SG We vill continue to monitor the performance of the control rod drives and keep the Re6 on I Compliance office 1
advised of our observations.
During the next refueling outage (presently scheduled for the spring.of 1972), drives 18-11 and 30-31 vill be replaced with rebuilt drives and they vill be disassembled and inspected.
We are enclosing twenty-five copies of this letter, Very truly yours, Uf?
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Ivan R. Finfro
, Jr.
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Manager, Nuclear Generating Stations IRF/pk Enclosures
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cc: Mr. J. P. O'Reilly, Director j
Division of Compliance l
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