ML20129B518
| ML20129B518 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 06/17/1985 |
| From: | Desando J TOLEDO EDISON CO. |
| To: | |
| Shared Package | |
| ML20129B463 | List: |
| References | |
| NUDOCS 8507290178 | |
| Download: ML20129B518 (6) | |
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TITLE:
NI-2 Count Rate Level Indication Failure Analysis REPORT BY:
Jack DeSando PLAN NO:
ISB DATE PREPARED: June 17, 1985 PAGE:
1 of 3 INTRODUCTION The following report is the analysis and evaluation to support the action plan for determining the root cause for the failure of NI-2, Count Rate Level Indication. This report has been prepared in accordance with the
" Guidelines to Follow when Troubleshooting or Performing Investigative Actions into the Root Cause Surrounding the June 9, 1985, Reactor Trip",
Rev. 2.
SUMMARY
OF DATA A.
Known Information and Operational Data for Conditions Prior To, During, and After the Transient 1.
Prior to the transient - NI-2 indicated less than 1 x 10-1 counts per second with the detector high voltage deenergized.
Source range detector high voltage is turned "off" when power exceeds 1 x 10-9 Amps as detected by both intermediate range channels (High Voltage Cutoff Bistable). A source range indica-tion of less than 1 x 10~1 counts per second, in this condition i
is normal.
2.
During the transient - As power decreased below 1 x 10-8 Amps, as detected by both intermediate range channels, the source range high voltage cutoff bistable reset, which, in turn, supplied high voltage to the source range detectors. At this time NI-2 indication remained at less than 1 x 10~1 counts per second. Under these conditions, NI-2 should have registered an on-scale indication.
i 3.
Af ter the transient - The I&C mechanic observed that the remote i
count rate level indication for NI-2, located on the control 1
console in the Control Room, indicated abnormally low at less than 1 x 10-1 counts per second. He then pt-oceeded to check the 3
local count rate level indication, located on the count rate amplifier module in Reactor Protection Systes (RPS) Channel 1.
Upon opening the cabinet doors for RPS Channel 1, the I&C mechanic observed a normal, on-scale indication on the local meter. He then rechecked the remote indication only to find l
that it was indicating normally, also. ST 5091.01 was performed to demonstrato operability on 5/9/85.
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1
B.
Maintenance History (Taken from I&C Equipment Record and DBMMS Data) 9/20/84 - Replaced the Output Calibration Trim Potentiometers on all test modules associated with Reactor Protection System Channel 1, including the Source Range Test Module for NI-2.
Trim Potentiometer replacement was in response to B&W safety concern, PSC 10-82 (SCN 75-6754). Physical replacement was performed under MWO 1-84-2846-00.
9/20/84 - Cleaned and inspected Reactor Protection System Channel 1.
Removed, cleaned, and inspected all modules associated with Reactor Protection System Channel 1, including modules associated with NI-2.
Cleaned and inspected all cabinet mounted hardware, including all module connector sockets, and checked all field wiring connections, at terminal strips in the bottom of the cabinets, for tightness.
Inspection was performed under MWO 3-84-1966-01.
0/23/84 - Replaced connector plug, located on the back of the Source Range Detector High Voltage Power Supply Module associated with NI-2.
During inspection performed per Step 2 above, two broken pins were found on Blue Ribbon Connector Plug (J1.0) for the Source Range Detector High Voltage Power Supply Module. Connector was replaced under MWO 1-84-2846-00.
3/25/85 - Source Range count rate level indication associated with NI-2 failed to less than 1 x 10-1 counts per second. NWO 1-85-1157-00 was generated to determine cause for NI-2 level indication failing low.
Upon opening the cabinet
- doors for Reactor Protection System Channel 1, the count rate level indication returned to normal.
ST 5091.01 was performed to prove operability. MWO 1-85-1157-00 was voided, no troubleshooting was performed.
4/13/85 - Source Range count rate level indication associated with NI-2 failed to less than 1 x 10-1 counts per second. MWO 1-85-1337-00 was generated to determine cause for failure. Prior to performing any troubleshooting, the I&C mechanic tapped on the front of the Count Rate Amplifier Module, associated with NI-2, and the count rate level indication returned to normal. A visual inspection of the Count Este Amplifier Module, associated connectors, and associated wiring was performed. No discrepancies were noted. ST 5091.01 was performed to prove operability.
CHANGE ANALYSIS According to the maintenance history, taken from I&C equipment records and from Davis-Besse Maintenance Management System data, and according to past operational experience, it is apparent that the failure of NI-2 was first experienced on 3/25/85. Just prior to this, during the 1984 refueling outage, all RPS modules were removed, cleaned, and inspected. This inspection revealed two bad pins on the blue ribbon connector plug on the source range detector high voltage power supply module associated with N1-2.
This connector was replaced and all modules were reinstalled on 9/23/84.
It is possible that during the cleaning or reinstallation of Page 2 of 3
i these modules, damage was done to cause an intermittent contact or connection and/or possibly a loose component.
HYPOTHESES Hypothesis for Failure of Count Rate Level Indication Associated with NI-2 to Less than.1 Counts Per Second i
l Based on the information received during the transient and information obtained from equipment records and DBMMS data, it appears that the high voltage to the Source Range Detector or the input signal to the Count Rate l
Amplifier Module is being interrupted by a bad contact, loose wiring and/or loose components. There are several areas that should be investigated:
1.
Loose or intermittent connection and/or component on Count Rate i
Amplifier Module.
2.
Loose or intermittent connection and/or component on Source Range Detector High Voltage Power Supply Module.
3.
Failure of Relay K1.0 in the Count Rate Amplifier Module.
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i ACTION PLAN EAN$odNIh PACTE o..
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gaTg~g,,, g, o-pg7PAME b sy NI-2 Failure Analysis 6-15-85 J. DeSando sPacaic osactive To determine root cause for Count Rate level indication associated with NI-2 failing low.
STED PHIME ASSIGNE D START TARGET DATE A I I
NUU8E Rj H F SPONSIBILITY TO DATE DATE COMPL ETED All. STEPS OF THIS ACTION PIAN ARE TO BE PERFORMED IN ACCORDANCE WITH THE LATEST REVISION OF "CUIDELINES TO FOLLOW WHEN TROUBLE-SHOOTING OR PERIVRMING INVESTICATIVE ACTIONS INTO THE ROOT CAUSES f
SURROUNDING THE JUNE 9. 1985. REACTOR TRIP".
l.
Measure and record all Source Range NI-2 instrumentation string _ J. DeSan_do_ __J._DeSa_ndo voltages at test Jacks on associated modules, also, note all T. Isley associated switch positions and Potentiometer settings.
2.
Remove the Count Rate Amplifier Module from the RPS cabinet J. DeSando J. DeSando and inspcet and troubleshoot for loose wiring and/or components.
T. Isley Also, check for proper mating between module plug and cabinet socket. Inspect viring at cabinet socket for loose connection.
Reinstall Count Rate amp module.
(Hypothesis Step 1) 3.
Repeat inspection / troubleshooting described in Step 2 for Source J. DeSc-Jo J. DeSando Range Detector High Voltage Power Supply module associated with T. Isley NI-2.
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NI-2 Failure Analysis._ __ _
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J.DeSando sri caric un a cuive To determine root cause for Count Rate level _indicallo_n_ Associated _With NI-2 failing_lotr-site
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^58"'4E D STAHI T AHM T DATE AcTum sites NuiWPSE H fM SPONSIBILIT Y TO DATE DAIE COMPLE TED 4.
Verify proper operation of relay _ Kl.0 in the Count _ Rate _ Amplifier _.._.JnDeSandq.__l,_DeSando_
Module associated with NI-2.
Monitor relcy contact performance.
T. Isley.
while switching Associated Source _ Range Test Module f_ Tom
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