ML20214L304

Forwards Written Repts for Occurrences 33 & 34 Re Main Steam Line Snubber Monitoring Sys,In Response to Confirmatory Action Ltr 85-04

ML20214L304
Person / Time
Site:	Dresden
Issue date:	04/21/1986
From:	Scott D COMMONWEALTH EDISON CO.
To:	James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
References
86-281, CAL-85-04, CAL-85-4, NUDOCS 8609100068
Download: ML20214L304 (2)

Text

• ^* Commonwealth Edison [

Dresden Nuclear Power Stition R.R. #1 Morris, Illinois 60450 Telephone 815/942-2920 April 21, 1986 DJS LTR: 86-281 James G. Keppler Regional Administrctor Director of Inspection and Enforcement Region III U.S. Nuclear Regulatory Commission 799 Roosevelt Road Glen Ellyn, Illinois 60137

Reference:

DJS Ltr.86-154 to J. G. Keppler from D. J. Scott, dated March 3, 1986.

Dear Sir:

This letter is in reference to the Confirmatory Action Letter 85-04 regarding the Main Steam Line Snubber Monitoring System for Dresden Unit 2. Item 2 of this Confirmatory Action Letter requires a verbal notification to Region III within 2 working days followed by a written report and safety evaluation within 30 calendar days.

Two occurrences have been identified during this reporting period:

Occurrence #33 Notification made to S. Stasek by J. Achterberg on March 26, 1986 Occurrence #34 Notification made to D. Danielson by G. Smith on April 3, 1986 The written reports and safety evaluations when required for these occurrences are attached.

Sincerely,

/

/

D. . Scott Station Manager Dresden Nuclear Power Station DJS:JW:hjb Enclosure cc: J. Almer J. Welch J. Achterberg J. Williams File / Misc.

File / Numerical 8609100068 860421 Yf b5j l DR ADOCK 0500 7 i i APR 2 31986

Occurrence #33 On March 24, 1986, at 1900 hours0.022 days <br />0.528 hours <br />0.00314 weeks <br />7.2295e-4 months <br /> Unit 2 was steady at 99.1% of rated (2504 MWt) and a load of 816 MWe when the strain gauge (SG) associated with snubber #46 instantaneously failed up-scale while the corresponding Linear Variable Displacement Transformer (LVDT) for that snubber exhibited no linear movement. Subsequent investigation detected a malfunction of the SG bridge circuitry. A short circuit to physical ground was indicated on one of the SG bridge conductors, rendering the device incapable of performing its intended function. Following the manual shutdown of April 2, 1986 (Occurrence #34), a visual inspection of the snubber was conducted. No abnormal conditions were noted at that time and readings taken indicated the short circuit to be in the cabling and not in the SG mounted on the end cap of the snubber. The cabling shall be repaired during the planned anubber inspection outage in May.

Occurrence #34 On April 1, 1986, at 1800 hours0.0208 days <br />0.5 hours <br />0.00298 weeks <br />6.849e-4 months <br />, a manual shutdown of Unit 2 was commenced for lack of control panel anchoring bolts. At approximately 0025 hour2.893519e-4 days <br />0.00694 hours <br />4.133598e-5 weeks <br />9.5125e-6 months <br /> and at 0418 several instrumentation monitor actuations were noted. At 0024 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> Unit 2 was at 28.2% of rated power (713 MWt) with a load of 200 MWe decreasing 50 MWe/hr while at 0418 hours0.00484 days <br />0.116 hours <br />6.911376e-4 weeks <br />1.59049e-4 months <br /> Unit 2 was off-line and at 0% of rated power.

After reviewing the sequence of events during shutdown, it was determined that the snubber instrumentation triggers occurred during the insertion of the source range monitors (SRM's) and intermediate range manitors (IRM's). These traces were compared and similarities noted to those obtained during testing on June 3, 1985, which is described in Occurrence #5. That occurrence was attributed to electrical interference generated from the movement of SRM's and IRM's. Since the unit shutdown progressed normally, no steamline tran-sients were identified and the source of these traces have been attributed to specific plant evolution (SRM/IRM movement), the safety significance of this event is minimal.

On April 17, 1986, at 0900 hours0.0104 days <br />0.25 hours <br />0.00149 weeks <br />3.4245e-4 months <br /> the snubber monitoring system was taken out of service to remove the Gould chart recorders and replace them with the Magedac data aquisition system. The snubber monitoring system was placed back in service on April 18, 1986 at 1510 hours0.0175 days <br />0.419 hours <br />0.0025 weeks <br />5.74555e-4 months <br />. During the system down time Unit 2 remained at a steady load of approximately 800 MWe with no operational tran-sients noted. Preliminary testing has indicated a possible reduction of spurious trips with the new system.

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