ML17252A910
| ML17252A910 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 05/06/1974 |
| From: | Stephenson B Commonwealth Edison Co |
| To: | O'Leary J US Atomic Energy Commission (AEC) |
| References | |
| BBS Ltr #326-74 | |
| Download: ML17252A910 (3) | |
Text
CommonvAlth Edison One First Na*t-Plaza, Chicago, Illinois AddressrJ~eply to: Post Office Box 767 q1J~~go, 'Iii no is 60690 BBS Ltr #326-74 Dresden Nuclear Power Station Mr. J. F. O'Leary, Director Directorate of Licensing U. S. Atomic Energy Commission Washington, D. C.
20545 R. R. #1 Morris, Illinois May 6, 1974 RtC[/V£D *
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SUBJECT:
LICENSE DPR-25, DRESDEN NUCLEAR POWER STATION, UNIT #3 1 REPORT OF ABNORMAL OCCURRENCE PER SECTION 6.6.B.l.a OF THE TECHNICAL SPECIFICATIONS TORUS LOW LEVEL RESULTING FROM FALSE LEVEL INDICATION AND RESULTANT OPERA TOR ACTION
References:
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Telephone:
Telegram:
Mr.
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Dear Mr. O'Leary:
I This letter is to report a condition relating to the the unit at about 2200. hours on April 27, 1974.
At this time, it was -;;n~....w-~
that the torus level indication bad increased after rejection of water had commenced.
The rejection of water had been initiated subsequent to receiving a high torus level alarm and indication.
This malfunction is *contrary to section 3.7.A.l, which requires a minimum water volume of 112,000 ft3 in the torus.
PROBLEM The unit was in the refuel mode with a water_ temperature of 80°F when the high level alarm annunciated.
This alarm initiates at -2". Shift personnel lined up the system to reject water to Unit 2/3 Radwaste and started the transfer. After pumping approximately 4900 gallons to radwaste, it was noted that the level indication had increase(Ct:o +l\\". The level transmitter (2-1626) was found to be indicating incorrectly when the operator visually observed the torus level to be noticeably low.*
Visual observation was possible since the torus access batches were open to the reactor building.
REGULATORY DOCI{ET FILE COPY 411'7
Mr. J. F. O'Le~~y
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May 6,- 1974
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- l'r The operator t~pped
- -the lo:!i point: µnpulse line several* 'times and the indication returned to actual level, which was -7 11
- The shift immediately started refilling the torus to bring the status into compliance.with the Technical Specifications.
An Instrument Mecbai1ic was called in to calibrate the transmitter to assure 'it was reading correctly.* calibration revealed proper indication and clear taps. - 'The torus was filled to -3.511 by 0350 hour~ on the 28th.
1 At this point, t~e torus level*was within compliance (Technical Specification range is -1%" _to -5\\").
The level transmitter provides torus level indication on pa~el 903-3. It also annunciates a Hi/Low level alarm on panel 903-3.
INVESTIGATION.
Prior to calibration, the impul~e lines were checked to be clear.
The tapping by the operator had apparently vibrated the transmitter sufficiently to clear whatever bad caused the false indication.
The upper and lower taps were checked: to be clear of obstructions by the Innrument Mechanic.
- Cali-bration of the indicator (transmit~er) verified proper functioning at. the time of. calibration. The transmitter, manufactured-by Barton -Co., bad been calibrated two days prior to. the occur.rence. It was found to be indicating approximately -k" *low at this.earlier ealibration. _The impulse taps were -
checked clear at this time* also.
- Investigation of the occurrence revealed. that there-was no physical reason for the initial high level alarm other than a transmitter problem.
Subsequent observation of.an increasing level i~dication during re1ection of water and correct indication after tapping the transmitter also indicate poor transmitter operation *
. CORRECTIVE ACTION -*
As mentloned, the transmitter was calibrated and the impulse legs were checked clear. There is presently no scheduled surveillance on the transmitter and procedures require operations to respond to the level indi-cation with no checks on level indication accuracy.
In the future, via a procedure revision and"a modification, the operator ~ill respond to a level alarm and/or improper level indication by visually checking level with-a sight glass which he can readily valve* in service at the transmitter. Operating'& response will be based on both the remote and actual level indication. If there is a discrepancy between the two sets of data, ansinstrument Mechanic will be immedi8tely called in to correct the problem.
.. ' ).
Mr. J. F. O'Leary-
- ~
~ *.l* May 6, 1974 The sigbt glass modification will be installed on both Unit 3 and Unit 2.
The valving to be used for this modification is presently installed as part of the existing level sensing system.
In addition to installation of the sight glass, tags will be placed on the valves indicating they are normally closed and should be opened only to check torus level under special circumstances.
A six month surveillance program requiring calibration_of the transmitter will also be instituted.
The surveillance will be started as of May 15, 1974.
EVALUATIONS Proper operation of the level transmitter had been verified two days prior to the occurrence. As indicated in the Technical Specifications Bases Section 3.7.A, "The pressure suppression chamber water volume must absorb the associated decay and structural sensible heat released during primary system blowdown from 1000 psig".
The limits specified for torus level and temperature are based on the volume of reactor coolant to be condensed during a blowdown.
The reactor mode switch was in refuel at the time of the oc.currence with moderator temperature at 800p and the reactor cavity was flooded.
Theref~re, the ability to maintain core flooded and cool under accident conditions was not affected by this occurrence.
The action initiated by shift personnel and the Instrument Mechanic were appropriate for the given conditions.
Since the same type of transmitter failur~ could occur during power operation, the corrective action indicated is mandatory.
Lack of proper level indication would be intolerable under this condition.
The installation of the sight glass and the procedure revision should eliminate any possibility of a similar occurrence.
There is no previous history of failure of this system.
During startup tests on Unit 2, the level sensing system was revised to a closed type sensing transmitter to avoid evaporation of the reference leg.
This occurrence poses no reason for limiting future operation of Unit 2 or 3.
BBS:JR:do Sincerely,
~~~ra*&~
B. B /Jstephenson Superintendent