ML17252A493

LER 74-031-00 for Dresden Unit 3 Regarding the 2/3 Core Height Water Level Sensors Lits 3-263-73 A&B Having Setpoints Above the Technical Specification Limit

ML17252A493
Person / Time
Site:	Dresden
Issue date:	10/08/1974
From:	Stephenson B Commonwealth Edison Co
To:	James Keppler US Atomic Energy Commission (AEC)
References
BBS Ltr.#736-74 LER 74-031-00
Download: ML17252A493 (3)

Text

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, , Commonwealt.lison One First National Plaza, Chicago, Illinois Address Reply to: Post Office Box 767 Chicago, Illinois 60690 BBS Ltr.#736-74 Dresden Nuclear Power Station R. R. #1 Morris, Illinois

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October 8, 1974 Mr. J~es G. Keppler, Regional Director_*

-Directorate of Regulatory Operations-Region III

u. s. ~tomic Energy- Commission 799 Roosevelt Road Glen Ellyn, Illinois 60137

SUBJECT:

REPORT OF ABNORMAL OCCURRENCE PER SEX:TION 6. 6.A OF THE TEX:HNICAL .

SPEX:IFICATIONS.

2/3 CORE HEIGlfl' YARWAY CALIBRATION DEFICIENCY.

References:

l) Regulatory Guide 1.16 Rev.l Appendix A

2) Notification of. ~egion llI of A&: 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 l Report Number: 50-249/1974-31 Report Date: October 8, 1974*

, Occurrence Date: September 28,

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• -: }"; Facility: Dresden Nuclear Power Station, Morr~s-, Illinois

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IDENTIFICATION OF OCCURRENCE The 2/3 core height water level sensors LITS 3-263-73 A&:B were found during routine surveillance to have setpoints above the Technical Specification limit of ~ 257" H2o 6 P 4ecreasing. --

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

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

10713 OCT 1 0 1-~JI4

Mr. James G. Keppler

• October 8, 1974 DF.SCRIPl'ION OF OCCURRENCE At 16oO hours on September 28,.1974, while performing routine surveillance testing of Unit #3 containment spray permissive Yarwaylevel sensors, LITS 3-263-73 A&B were found with setpoints ef 259.5 inches of H~ 6 P decreasing and 257*5 inches of H2o 4P decreasing respectively. The Technical Specifi-cations requires that the sensors operate at s 257 inches H20 /4 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.

DF.sIGNATION OF APPARENT CAUSE OF OCCURRENCE (Deficient Procedures)

The apparent cause of the.occurrence is the instrument mechanic either trapping air bubbles in the sensor during test equiJ;IJlent connection to the .Yarway, decreasing the H20 4,p at a slower rate than was used during adjustment of the setpoint, or i;i,ot taking into consideration the instrument hysteresis characteristi_cs.

ANALYSIS OF OCCURRENCE On October 4 and 5, 1974, testing of LITS3-263-73 A&:B Wa.s accomplished to determine the possible cause for the out of specification setpoint readings obtained on September 28, 1974. The folloWi.ng was determined to affect the setpoint readings. The system was operated and determined to have instrument

• repeatability within 1/2 percent of full range meter indication *. Meter indi-*

cation :1;s)o-4oo inches. Indicator hysteresis specification is ~ maximum of full-scale meter indication.

1. During equiJ;IJlent connection an air bubble or bubbles may have been trapped on the low preseure line of the Yarway. Testing verified that r

.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 indication;

2. When checking the setpoint, the rate at which the H20 6 P is reduced across the detector could affect the setpoint reading. Subsequent test confirmed that the faster the H20 4P is reduced, the lower the setpoint reading is. (It is not known if the instrument mechanic reduced H20 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 H20 6 P is increased above .the reset point of the interlock and then decreased to the set:Point, the setpoint reading is decreased due to hysteresis. It is not known if the instrument mechanic who adjusted the setpoint incorporated the instrument hysteresis when adjusting the setpoint. 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 hysteresis characteristic, the setpoint readings would have been within Technical Specifications.

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Mr. James G. Keppler October 8, 1974 The normal setpoint of these switches is 96/l44ths core height. The out of specification trip points would have been 96.9/l44ths and 96.2/l44ths. 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 LPCI system in.the containment cooling mode. Even though the setpoint was low, the operator would have verified the vessel level before manually initiating the containment cooling. Therefore, this situation did not present a safety hazard to either plant personnel or the general public.

CORREX:TIVE ACTION The* corrective action was to reset the interlock settings to as close*to 254 inches H20 '~ 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 4418&:: devices. The switches were last checked Augustl9, 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 fo\Uld to be within Technical Specifications. LITS 3-263-73B has failed four times since September, 1971 with the last failure occurring in ~ovember, 1973. Each month since November, the sensor/indicator was found to be within Technical Specif~cations.

Sincerely,

.A.f.J)~

Ln ~.~.* St~enson

'/!"...-Superintendent BBS:GC:do