ML20084R874

AO 50-249/74-31:on 740928,core Height Water Level Sensors Lits 3-263-73 a & B Found W/Setpoints Above Tech Spec Limit. Apparently Caused by Trapped Air Bubbles in Sensor or Not Considering Instrument Hysteresis

ML20084R874
Person / Time
Site:	Dresden
Issue date:	10/08/1974
From:	Stephenson B COMMONWEALTH EDISON CO.
To:	James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML20084R875	List: ML20084R874 ML20084R921
References
736-74, AO-50-249-74-31, NUDOCS 8306150641
Download: ML20084R874 (3)

Text

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Address Reply to: Post Ofhce Box 767 Chicago, !!hnois 60693 EDS Ltr.#736-74 Dreaden !!uelcar Power Station R. R. #1 Morris, Illinois 60450 c* '.

October 8, 1974 f

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R Hr. James G. Keppler, Regional Director -

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Directorate of Regulatory Operations-Region III I 9:i /

U. S. Atomic Energy Co::=ission l*f s .y, ' g, 799 Roosevelt Read

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Glen Ellyn, Illinois 60137 9 <( n SUBJE T: REPORT OF APl:ORMAL OCCURRM!CE PER SECTION 6.6.A 0F THE TECHNICAL SPECIFICATIO.NS.

2/3 CORE HEIGHT YAR'3AY CALIPRATION DEFICID]CY.

References:

1) Regulatory Guide 1.16 Rev.1 Appendix A

2) Notification of Region III of AEC Regulatory Operations Telephone: Mr. C. Brown,1600 hours0.0185 days <br />0.444 hours <br />0.00265 weeks <br />6.088e-4 months <br /> on September 30, 1974 Telegram: Mr. J. Keppler, 1620 hours0.0188 days <br />0.45 hours <br />0.00268 weeks <br />6.1641e-4 months <br />'on September 30, 1974

3) Drawing Number: GEK 26915 Tab 1 Report Number: 50-249/1974-31 Report Date: October 8, 1974 Occurrence Dato September 28, 1974 Facility: Dresden Nuclear Power Station, Morris, Illinois IDH7PIPICATION OP OCCURREJCE The 2/3 core height water level sensors LITS 3-263-73 A&B were found during routine surveillance to have setpoints above the Tecimical Specification limit of ,g_ 257" H O 2 6 P decreasing.

The "as found" setpoints did not mcot the requirement of Table 3.2.2 of the Technical Specifications which requires that the containment spray system bc interlocked to prevent operation if reactor water IcVel is at or below 2/3 of the coro height.

CONDITIONS PRIOR TO OCCURRE3CE Unit #3 was operating in a steady state plant condition of 700 IGt and 200 IMe. Routine surveillance " Containment Spray Interlocks, Reactor Water i Level" on containment spray permissive Yarway level sensors LITS 263-73A&B

. was in progress.

I 8306150641 741008 COPY SENT REGION  % ~5 PDR ADOCK 05000249 S PDR . g . g c, 10'l.l 2

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Mr. James G. Kepp.__) October 8, 1974 DESCRIPPION OF OCCURRDICE -

At 1600 hours0.0185 days <br />0.444 hours <br />0.00265 weeks <br />6.088e-4 months <br /> on September 28, 1974, while performing routine surveillance testing of Unit #3 containment spray permissive Yarway level sensors, LITS 3 263-73 A&B were found with setpoints of 259 5 inches of H 2O 6 P decreasing and 257.5 inches of H2 O 6 P decreasing respectively. The Technical Specifi-cations requires that the sensors operate at S_ 257 inches H2O 6 P decreasing.

The instrument mechanic operated the sensor and indicating instrument several times to verify obtained readings and observed the indication to decrease to settings within Technical Specification limits.

DESIGNATION OF APPARD7P CAUSE OP OCCURRE!CE (Deficient Procedures)

The apparent cause of the occurrence is the instrument mechanic either trapping air bubbles in the sensor during test equipnent connection to the Yarway, decreasing the H2 O 6 P at a slower rate than was used during adjustment of the setpoint, or not taking into consideration the instrument hysteresis characteristics.

ANALYSIS OF OCCURREICE On October 4 and 5, 1974, testing of LITS 3-263-73 A&B was accomplished to determine the possible cause for the out of specification setpoint readings obtained on September 28, 1974. The following was determined to affect the setpoint readings. The system was operated and determined to have instru=ent repeatability within 1/2 percent of full range meter indication. Meter indi-cation is 0-400 inches. Indicator hysteresis specification is 2 % maximum 4

of full-scale meter indication.

1. During equipnent connection an air bubble or bubbles may have been trapped on the low pressure line of the Yaruay. Testing verified that

,if an air bubble or bubbles is trapped that an initial high reading will occur and could be decreased to within setpoint tolerance by repeating attempts to verify the setpoint indicition.

2. When checking the setpoint, the rate at which the H 2O 6 P is reduced across the detector could affect the setpoint reading. Subsequent test confirmed that the faster the H2O 6 P is reduced, the lower the setpoint reading is. (It is not known if the instrument mechanic reduced H 2O 6 P at approximately the same rate as the instrument mechanic who adjusted the setpoint.)

3. The hysteresis of the instrument may have affected the setpoint reading.

When 2H O 6 P is increased above the reset point of the interlock and then decreased to the setpoint, the setpoint reading is decreased due to hysteresis. It is not known if the instrument mechanic who adjusted the actpoint incorporated the instrument hysteresis when adjusting the actpoint. It is known that the instrument mechanic checking the setpoint did not incorporate the instrument hysteresis characteristics. It is also known that if the instrument mechanic had incorporated the hyster'. sis characteristic, the setpoint readings would have been within Technical

. Specifications.

Mr. James G. Kep p 7 O Octob:r 8, 1974 V b The normal setpoint of these switches is 96/144ths core height. The out of specification trip points muld he.ve been 96.9/144ths and 96.2/144ths. The function of the sensors is to provide a permissive to allow the use of the containment spray system. The as found settings would have allowed contain-ment spray at 96.2/144ths of core height.

Station abnormal procedures state that the reactor vessel level be normal prior to utilizing the LICI system in the containment cooling mode. Even though the setpoint was low, the operator would have verified the vessel level before canually initiating the containment cooling. Therefore, this situation did not present a safety hazard to either plant personnel or the general public.

CORRDCTIVE ACTION The corrective action was to re' set the interlock settings to as close to 254 inches H2 O o P as possible. Further action is to change the procedure to identify the hysteresis characteristics of the Yarway indicator and assure the characteristics are taken into consideration when checking the setpoint and to take steps necessary to assure air bubbles are not trapped in the detector.

FAILURE DATA The sensors are Yarway Number 4418EC devices. The switches were last checked August 19, 1974 and found to be with Technical Specifications. This occurr-ence is not considered a sensor failure but a failure to connect test equip-ment correctly or a failure to consider equipment characteristics when checking the setpoint. However, previous to this Technical Specification violation, LITS 3-263-73A has failed six times since September,1971 with the latest failure occurring in May, 1974 Each month since May, the sensor / indicator was found to be within Technical Specifications. LITS 3-263-733 has failed four ticca since September, 1971 with the last failure occurring in November, 1973. Each month since November, the sensor / indicator was found to be within Technical Specifications.

Sincerely, l - M

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Superintendent BBS:GC:do

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