ML20003C386

Ao:On 731216,during Operation at Steady Load of 734 Mw,Trip Signal Received from Main Steam Line High Flow Sensor DPIS-261-2S.Caused by Personnel Failure to Open Instrument Valve After Surveillance.Valve Opened

ML20003C386
Person / Time
Site:	Dresden
Issue date:	12/24/1973
From:	Worden W COMMONWEALTH EDISON CO.
To:	Oleary J US ATOMIC ENERGY COMMISSION (AEC)
References
NUDOCS 8103030239
Download: ML20003C386 (2)

Text

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. [egulatory. . .

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• k N _ ,,e]/ One First Ratro Address Reply to: Post Offee Box 767 Chicago, Illinois 60690 A-I* D Dresden Nuclear Power Station R. R. #1

@ Morris, Illinois 60450 91l Il- '

December 24, 1973 @ \

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==Wn"&s1 rau p$4 0 / c gt s-D Mr. J. F. O'Ieary Directorate of Licens *, a @ p # }'

U. S. Atcnic Energy Cacmissicn Washington, D.C.

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SUBJECT:

LICENSE DPR-19, DRESDEN NWAR POMR STATION UNIT #2 REPORT OF ABNTMAL OCCURRENCE Pm SECTION 6.6.B.10F THE TECHNICAL SPECIFICATI0?s.

MAIN STEAM LINE HIGH FLOW SE? EOR FAII11RE.

References:

1) Notification of Region III of AEC Regulatory Operaticus Telephone: Pr. Maura, 1600 hours0.0185 days <br />0.444 hours <br />0.00265 weeks <br />6.088e-4 months <br /> on Dece=ber 17, 1973.

Telegram: Mr. Keppler, 1630 hours0.0189 days <br />0.453 hours <br />0.0027 weeks <br />6.20215e-4 months <br /> on December 17, 1973.

2) Dwgs: P & ID M-12 ani 12E2501

Dear Mr. O' Leary:

This letter is to report a condition relating to the operation of the unit at about 1659 hours0.0192 days <br />0.461 hours <br />0.00274 weeks <br />6.312495e-4 months <br /> on December 16, 1973. At this time a trip signal was received from Main Steam Line High Flow Sensor 261-2S. This initiated a channel "B" trip for the Group I Isolation System.

This malfunction is contrary to section 3.2.A. of the Technical Specifications.

PROBLD4 At the time of the occurrence, Unit 2 was operating at a steady load of 734 MWe. At about 1659 hours0.0192 days <br />0.461 hours <br />0.00274 weeks <br />6.312495e-4 months <br />, a trip signal was received from DPIS-261-2S. This switch indicates a high steam flow condition in Main Steam Line "D". The instrume: tation in the control room was observed to be normal. Load was then dropped 45 MWe, but the switch did not reset. An inspecticn was made of the instrument rack and switch 261-2S was found to be reading approximately 130 paid. The other three sensors which also monitor "D" Main Steam Line were noted to be indicating approximately 76 psid. The valves on switch 261-2S were checked and the low side manifold valve was found to be only slightly open. The valve was fully opened and the indicated differential pressure of 130 psid dropped to 76 psid, which was the same reading as the other three sensors on Main Steam Line "D".

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r Mr. J. F. O'Ieary O O December 24, 1973 INVESTlGATIDN It was speculated that the cause of the abnormal trip of DPIS-261-2S was due to the low pressure instrument valve being left closed after the last scheduled surveillance on December 12, 1973. However, to achieve a high differential pressure with the low pressure instrument valve closed it would be necessary to have a laak in the low pressure side of the instrument.

To verify this assumption, the low pressure valve was closed again, end instrument differential pressure was observed. The pressure slowly increased, which indicated a small leak in the instrument or in the piping.

Isak detection solution was applied to all piping connections with no definite results. All fittings were then tightened and a moderately loose "swagelok" nut was found. The low side pressure valve was again closed on the instrument and the differential pressure stayed constant. In addition, an inspection was made of all moving parts on the instrument and water was forced through the instrument manifold to assure no passages were plugged.

It is therefore concluded that the cause of the occurrence was failure to open an instrument valve after a scheduled surveillance.

CORREchvn ACTION The immediate corrective action was to open the low pressurt, instrument valve en DPIS-261-2S. The instrument mechanic who did the last surveillance was informed of the problem, but believes he did not leave the valve closed. The man is fully aware of the seriousness of the problem.

Failure to leave valves in their proper operating condition is a problem that occurs infrequently.

EVAIDATION The high steam flow portion of the Group I Isolation System consists of four high flow sensors per steam line. The system is designed to allow as many as two of the four flow switches to malfunction before an isolation is initiated. Therefore, the malfunction of switch DPIS-261-2S did not degrade the operation of the system because the malfunction was in the safe direction. Consequently, the saf4y of plant personnel arri the general public qs not jeopardized.

Cumulative experience with th'.s type of malfunction at Dresden does not exist. This malfunction does not represent an addition to an unsafe trend.

Sincerely yours, baEAlMam f W. P. Worden

.j Superintendent

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