ML20154L570

Forwards Repts & Safety Evaluations Re 860106,07 & 12 Linear Variable Displacement Transformer Spike occurrences,860121 Reactor Scram & 860123 & 29 Snubber Instrumentation Monitor Actuations

ML20154L570
Person / Time
Site:	Dresden
Issue date:	02/04/1986
From:	Scott D COMMONWEALTH EDISON CO.
To:	James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML20154L512	List: ML20154L509 ML20154L570
References
86-80, CAL-85-04, CAL-85-1, CAL-85-4, NUDOCS 8603110516
Download: ML20154L570 (4)

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7 Commonwealth Edison

) Dresden Nuclear Power Station

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R.R. #1 k

] Morris, Illinois 60450 (j Telephone 815/942-2920 February 4, 1986 DJS LTR: 86-80 James G. Keppler Regional Administrator Director of Inspection and Enforcement Region III U.S. Nuclear Regulatory Commission 799 Roosevelt Road Glen Ellyn, Illinois 60137

Reference:

DJS Ltr. 85-1187 to J. G. Keppler from D. G. Scott,' dated

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December 30, 1986.

Dear Sir:

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

Five occurrences have been identified during this reporting period:

Occurrence #26 Notification made to J. Harrison by E. Armstrong on January 8, 1986.

Occurrence #27 Notification made to D. Danielson by E. Armstrong on January 12, 1986.

Occurrence #28 Notification made to I. Yen by J. Achterberg on January 23, 1986.

Occurrence #29 Notification made to D. Danielson by J. Achterberg on January 24, 1986.

Occurrence #30 Notification made to D. Danielson by E. Armstrong on January 31, 1986.

The written reports and safety evaluations when required for these occurrences are attached, sincerely,

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D. J. Scott Station Manager Dresden Nuclear Power Station DJS:JW:hjb Enclosure cc: J. Almer J. Welch J. Achterberg J. Williams FEB 7 1986 File / Misc.

File / Numerical 3 0603110516 960 PDR ADOCK O m

PDR S

5 Occurrence #26 On January 6, 1986 at 2107 hours0.0244 days <br />0.585 hours <br />0.00348 weeks <br />8.017135e-4 months <br /> the Linear Variable Displacement Transformer (LVDT) for snubber #50 exhibited a step function of 1.2 inches in magnitude, with a rise time of 5 milliseconds. At that time no corres-ponding force signature on the strain gage (SG) for snubber #50 was noted nor did any other SG or LVDT show a response. The signal returned to its normal level within 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />. The cause of the step function is likely due to a malfunction within the vishay amplifier or the AC/DC excitation module for the LVDT channel. The problem is intermittent, and the cause of the failure has not been determined. To verify that no mechanical failures of the LVDT had occurred, snubber #50 was viaually examined following the scram of January 21, 1986 (Occurrence #18). .No abnormalities were noted at that time.

On January 7, 198L at 1600 hours0.0185 days <br />0.444 hours <br />0.00265 weeks <br />6.088e-4 months <br /> to 1655 hours0.0192 days <br />0.46 hours <br />0.00274 weeks <br />6.297275e-4 months <br /> 4 spikes above the trip level were received on the LVDT for snubber #50. Unit 2 was at 98.5% power (2514 MWt) with a load of 821 MWe. A review of the operators log book and computer printouts for reactor pressure and steam flow showed no operational transients occurring at that time.

The SG associated with snubber #50 showed no corresponding force signature nor did any other SG or LVDT show any corresponding movement. With the large linear movements in the signals and their short duration (5-10 milli-seconds) this actuation is attributed to spurious electrical noise and not an actual pipe movement. The source of the noise remains undetermined.

Occurrence #27 On January 12, 1986 at 1000 hours0.0116 days <br />0.278 hours <br />0.00165 weeks <br />3.805e-4 months <br />, Unit 2 was operating at a steady power of 88% (2224 MWt) and a load of 727 MWe. An orderly increase of power to 93.1% (2352 MWt) and a load of 770 MWe was commenced at 1038 hours0.012 days <br />0.288 hours <br />0.00172 weeks <br />3.94959e-4 months <br /> and completed at.1100 hours0.0127 days <br />0.306 hours <br />0.00182 weeks <br />4.1855e-4 months <br />. Daring this time 4 spikes occurred on the strain gage (SG) on'unubber #53 at 1006, 1050, 1050, and 1054 hours0.0122 days <br />0.293 hours <br />0.00174 weeks <br />4.01047e-4 months <br />. The magni-tude of these spikes were 16, 17, 17, and 19 kips respectively, with a duration of less than 4 milliseconds. Subsequently, a spike occurred on the Linear Variable Displacement Transformer (LVDT) on snubber #53 at 1105 hours0.0128 days <br />0.307 hours <br />0.00183 weeks <br />4.204525e-4 months <br /> which had a magnitude of 1.4 inches and a duration of less than 4 milliseconds. All of these spikes were of an isolated nature and no other movement or forces were denoted on the other SG or LVDT.

The SG spikes were of large magnitude and short duration and the fact that there was no corresponding LVDT movement indicates that the spikes were caused by electrical noise. Similarly, with the large linear movements indicated by the chart record of the LVDT signals (outside design limits of the snubber) this actuation is also attributed to spurious electrical noise and not an actual pipe movement. The source of the noise remains undeter-mined.

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Occurrence #28 On January 21, 1986 at 12:45 hours Unit 2 scrammed from 45.9% power (1160 MWt) and a load of 360 MWe. The scram occurred during a reactor level instrument calibration surveillance. Following the scram, several spikes were observed on the strain gages (SG) and Linear Variable Displacement Transformers (LVDT's) associated with all of the snubbers. After reviewing the sequence of events during the scram, it was determined that the snuhher instrumentation triggers occurred during the insertion of the source range monitors (SRM's) and the intermediate range monitors (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 fron the movement of the SRM's and IRM's. Since no abnormalities or unusual nteam line transients were identified and the source of the traces have bein attributed to a specific plant evolution (SRM/IRM movement), the safety significance of ,

this event is minimal.

Occurrence #29 On January 23, 1986 Unit 2 began an orderly startup following the scram of*

January 21, 1986 (Occurrence #29). The unit was synchronized to the grid, at 1810 hours0.0209 days <br />0.503 hours <br />0.00299 weeks <br />6.88705e-4 months <br /> and a power increase was commenced. Soon after synchronizing to the grid, condenser vacuum anomalies were noted. As a preventive measure the unit was manually taken off line and put in hot standby to determine the root cause of the vacuum problem.

During the unit startup and shutdown, several scubber instrumentation l monitor actuations were noted. After reviewing *he sequence of events during startup and shutdown, it was determined that the snubber instrumen-tation triggers occurred during the withdrawat and insertion of the source range monitors (SRM'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 startup and shutdown progressed normally, no steam line transients were identified s and the source of these traces have been attributed to a specific plant evolution (SRM/IRM movement), the safety significance of this event is minimal.

Occurrence #30 On January 29, 1986 after the source of the condenser vacuum problem whicyforcedtheshutdownoftheunitwasfoundandrepaired,anorderly startup was commenced. The unit was placed in the run mode at 0633 hours0.00733 days <br />0.176 hours <br />0.00105 weeks <br />2.408565e-4 months <br /> and synchronized to the system grid at Q933 hours.

During the unit startup several snubber instrumentation monitor actuations were noted. After reviewing the sequence of events during the startup, it

( was determined that the snubber instrumentation triggers occurred during

( the withdrawal of the source range monitors (SRM's) and the int'e rmediate range monitors (IRM'si. 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 k

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generated from the movement of the SRM's and IRM's. Since the unit start-up progressed normally, no steam line transients were identified and the source of the traces have been attributed to a specific plant evolution (SRM/IRM movements), the safety significance of this event is minimal.

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