ML20059D118
| ML20059D118 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 08/21/1993 |
| From: | AFFILIATION NOT ASSIGNED |
| To: | |
| References | |
| OLA-2-I-MFP-145, NUDOCS 9401070012 | |
| Download: ML20059D118 (15) | |
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MANAGEMENT
SUMMARY
on April 28 1992, at 1249 PST with Unit 1 in Mode 1 (Power Opetotion) at 100 percent power, a containment ventilation isolation (CVI) actuation occurred. This event constitutes an Engineered Safety Feature (ESF) actuation. A four-hour, non-emergency report was made to the NRC in accordance with 10CFR 50.72 (b) (2) (ii) on April 28 at 1429.PST.
Radiation monitor RM-14B (plant ~ vent' radioactive gas monitor) output signal exceeded its alarm setpoint, causing the CVI actuation.
The operators determined that the CVI was due to a spurious high radiation alarm because the redundant monitor (RM-14A) did not detect any elevated activity level. After verifying that no high radiation conditions' existed and RM-14B responded normally, the control room operators reset the CVI logic and restored the containment ventilation system to its normal mode of operation.
During similar work on Unit 2, the I&C technicians discovered a loose connection in the test box being used on RM-28B at the time of the Unit 1 event. This test box is used for testing on RM-14 and RM-28 only. This discovery provides strong circumstantial evidence that this event was caused by an electronic noise created by the loose i connection in the test box. l As part of the corrective actions to prevent recurrence, (1) an I&C maintenance bulletin will.be written to cover the event and precautions to take during similar maintenance activities, (2) training'on this event will be included in.
the I&C quarterly maintenance seminar,-(3) discussions will be held in a tailboard on precautions to take during similar maintenance activities on radiation monitors (4) I&C technicians will make a one time visual inspection of other test boxes to identify similar connector problems.
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't NCR DC1-92-TI-N020 Rev. 00 l June 24, 1992 NCR DC1-92-TI-N020 CVI DUE TO A SPURIOUS HIGH RADIATION SIGNAL ON RM-14B l
I. Plant Conditions Unit 1 was in Mode 1 (Power Operation) at 100% power.
II. Description of Event A. Description of event:
On April 28 1992, at 1249 PST with Unit 1 in Mode 1 (Power Operation), a containment ventilation isolation (CVI) actuation occurred. This event coretitutes an Engineered Safety Feature (ESP) aceuation. A four-hour, non-emergency report was made to the NRC in accordance with 10CFR
- 50. 72 (b) (2) (ii) on April 28 at 1429 PST.
Radiation monitor (RM) 14B (IL) (MON) (plant vent radioactive gas monitor) output signal exceeded its alarm setpoint, causing the CVI actuation.
The redundant monitors did not detect any elevated activity level. Therefore the response of RM-14B was considered spurious. RM-28B also indicated an abnormal signal output, but below its high alarm setpoint limit.
After verifying that no high radiation conditions existed and RM-14B responded normally, the control l room operators reset the CVI and returned the l
affected systems to their normal operating. modes. '
During similar work on Unit 2, the I&C technicians discovered a loose connection in the test box being used on (RM) 28B (IL) (MON) at the time of the Unit 1 event. This test box is used for test on RM-14 and RM-28 only. This discovery provides strong circumstantial evidence that this event was caused by an electronic noise created by the loose connection in the test box. l B. Inoperable Structures, Components, or Systems that Contributed to the Event:
None.
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5 NCR DC1-92-TI-N020 Rev. 00 I June 24, 1992 l
1 i
C. Dates and Approximate Times for Major Occurrences:
- 1. April 28, 1992; 1249 PST: . Event / discovery ;
date. Alarms and other indications in the control room indicated an ESF actuation.
l 2. April 28, 1992; 1429 PST: A four-hour, non-emergency report was made to the NRC in accordance with 10 CFR 50.72(b)
(2) (11) .
F. Other Systems or Secondary Functions Affected:
None.
G. Method of Discovery:
The event was immediately apparent to plant operators due to alarms and indications received in the control room.
H. Operator Actions:
The operators determined that the CVI was due to a spurious high radiati:. alarm because-the redundant monitor (RM-14A) did not detect any elevated activity level. After verifying that no high radiation conditions existed and that RM-14B now responded normally, the control room operators reset the CVI logic and restored the containment ventilation system to its normal mode of ,
l operation.
l I. Safety System Responses: 1 All containment isolation valves closed as designed.
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l l 't i NCR DC1-92-TI-N020 Rev. 00 l June 24, 1992 l
III. Cause of the Event A. Immediate Cause:
The immediate cause of the CVI was a spurious l alarm from RM-14B. !
1 B. Root Cause:
The root cause of this event is a loose connector I on the test box used during maintenance on RM-28B. 1 The loose connector resulted in generation of ;
electronic noise. This not only affected the !
channel under test, but also resulted in I
electronic noise in the circuitry RM-14B. The l output of RM-14B exceeded its alarm setpoint and ultimately led to the CVI.
IV. Analysis ol__th_e Event I 1
A. Safety Analysis:
A CVI is a conservative actuation regardless of plant conditions. If an actual high radiation condition had occurred during the event, the I ventilation systems would have been ready to perform their accident prevention function.
Consequently, this event did not adversely affect i the health and safety of the public.
B. Reportability:
1.
Reviewed under QAP-15.B and determined to be non-conforming in accordance with Section 2.1.2. l
- 2. Reviewed under 10 CFR 50.72 and 10 CFR 50.73 per NUREG 1022 and determined to be potentially reportable in accordance with 10 CFR 50.72 (b) (2) (ii) arid 10 CFR 50. 73 (a) (2 ) j (iv). The report associated with this NCR is LER 1-92-005-00.
I
- 3. This problem will not require a 10 CFR Part 21 report, since it is being evaluated under 10 ;
CFR 50.72 and 50.73, and does not involve i defects in vendor-supplied services or spare j parts in stock.
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I NCR DC1-92-TI-N020 Rev. 60 June 24, 1992 1
- 4. This problem will not be reported via an INPO Nuclear Network entry.
- 5. Reviewed under 10 CFR'50.9 andLdetermined:the' event was not reportable under 10 CFR 50.9 since event was being reported under 10 CFR 50.73.
- 6. Reviewed under the criteria 'fo AP C-29 requiring the issue and approval of an OE and determined that no OE is required.-
V. Corrective Actions A. Immediate Corrective Actions:
(
! After verifying that no high radiation conditions existed and that'RM-14B now responded normally, '
the control room operators reset the CVI logic and restored the containment ventilation' system to its normal mode of operation.
In addition, after discovering a loose' connection, .;
the I&C' technicians repaired the test box used on RM 28B.
! B. Investigative Actions:
- 1. Review the data from the PPC:to determine any .
trend. l RESPONSIBILITY: T. Eubank ,
DEPARTMENT: I&C Maintenance l Tracking AR: A0264889, AE # 1 j STATUS: COMPLETE /
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The PPC data from 4/28/92 from 1150-1340 was l
! obtained. The additional-information did not !
l change conclusions' drawn from the. original I data obtained. .However, it did further solidify evidence'that'the event took place during associated work on RM-28B.
- 2. Measure the DC and AC. voltage on the high voltage power supply to determine'if the measurements taken affected the RM-28B or.RM-14B count rate.
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NCR DC1-92-TI-N020 Rev. 00 June 24, 1992 RESPONSIBILITY: D. Weatherby DEPARTMENT: I&C Maintenance Tracking AR: A0264889, AE # 2 STATUS: COMPLETE.
Measurements taken did not result in any change in output levels. However it was noted that the test box used to take the readings had been repaired aftat similar measurements on Unit 2 RM-28B resulted in fluctuating readings. Subsequent' investigation indicated that a test box connector was degraded. The faulty connector was repaired before the measurements for this investigative activity were taken. This event coupled with other available information provides strong circumstantial evidence that this was the cause of the event.
- 3. Investigate if there are any common conduits or raceway on signal or high voltage lines.
Signal cables for RM-14B and RM-28B share a common conduit (KK213). No other high voltage signal lines share common conduit or raceway for these two monitors. i l
- 4. Investigate welding, ocaffolding and I possible work in the vicinity of the radiation monitors.
A review of the signals received prior to and during the event indicates that they were not caused by a one time jar or bump. This review in conjunction with the interviews with the personnel working with the scaffolding indicates that this event was not' caused by the personnel erecting the scaffolding.
A review of the welding records indicates that no welding was being performed anywhere in the area at the time immediately before or during the event.
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-NCR DCl-92-TI-N020 Rev. 00 June 24, 1992 C. Corrective Actions to Prevent Recurrence:
- 1. Write an I&C maintenance bulletin to cover the event and precautions to take during similar. .
maintenance activities .
RESPONSIBILITY: D. Weatherby ECD: 06/25/92 DEPARTMENT: I&C Maintenance Tracking AR: -A0264889, AE.# 5 ,
Outage Related? No'
! OE Related? No NRC Commitment? Yes CMD Commitment? No ,
- 2. Upon completion and approval of the maintenance bulletin submit a TIP to be included in the I&C quarterly' maintenance seminar. The action will be considered complete when the TIP number is issued.
RESPONSIBILITY: D. Weatherby ECD: 06/25/92' DEPARTMENT: I&C Maintenance l Tracking AR: A0264889, AE #.6:
Outage Related?:No OE Related? No NRC Commitment? Yes CMD Commitment? No
- 3. Discussions will be held in a tailboard on precautions to take during similar maintenance activities on radiation. monitors.
RESPONSIBILITY: D. Weatherby ECD: 06/25/92 DEPARTMENT: .I&C Maintenance Tracking AR: A0264889, AE' # 7 '
Outage Related? No OE Related? No NRC Commitment? Yes CMD Commitment? No
- 4. I&C technicians will make a one time visual-inspection of other test boxes to identify similar connector problems, i
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l t 1 NCR DCl-92-TI-N020 Rev. 00 June 24, 1992 RESPONSIBILITY: D. Weatherby ECD: 07/3/92 DEPARTMENT: I&C Maintenance Tracking AR: A0264889, AE # 8 Outage Related? No OE Related? No NRC Commitment? Yes CMD Commitment? No D. Prudent Actions None.
E. Tracking AR: A0264889. j VI. Additional Information A. Failed' Components:
None.
B. Previous Similar Events:
Similar spurious system initiations were. reported.
in a number of LER's and NCR's, including LER:2-85-005, DC2-85-008, NCR DC2-86-TI-N041, and DCl-91-EM-N041. Although these previous LER's and NCR's' discuss various' spurious actuations, all of 1 the corrective actions taken would'not have I precluded recurrence-of.thetCVI-reported in?LER 1-92-005.
- 1. LER 2-85-008, Containment Ventilation Isolation" This LER reported a CVI caused 147 a spurious spike in the containment Gaseous Radiation monitor.RM-
- 11. The cause of this event'had not been determined. This event and other spurious actuations studied by the newly formed-Noised Reduction Task Force-to determine the source (s)-
and corrective actions to prevent' recurrence of spurious signalsidid'not prevent the current LER.
- 2. LER 2-85-008, " Containment Ventilation Isolation"-
This LER reported a_.CVI caused by'a spurious spike.
in the gaseous radiation monitor.RM-14A. The spurious spikes were initiated by electromagnetic 92NCRWP\92TINO20.PGD Page .8 of 15- ,
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NCR DC1-92-TI-N020 Rev. 00 June 24, 1992 signals generated during switching in the 500KV yard. This event and other spurious actuations studied by the newly formed Noised Reduction Task l Force to determine the cause(s) and corrective actions to prevent recurrence of spurious signals did not prevent the current LER.
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- 3. NCR DC-2-86-TI-N041, " Containment Ventilation Isolation due to electronic noise and late issuance of a 10 CFR 50 72 required report due to inadequate guidance" This NCR reported a CVI due to electronic noise generated when RM-13 was energized. The late reporting was due to inadequate guidance contained in procedure concerning the reporting of ESF actuations. The time delay circuitry change ,
installed in radiation monitors that actuate the CVI system and revision of the procedure on reporting ESF actuations did not prevent the current LER.
- 4. NCR DC1-91-EM-N041, "CVI due spurious RM-11 high-rad alarm" This NCR reported a CVI due to spurious high radiation alarm from containment air p rticulate monitor RM-11. The root cause for the spurious high radiation alarm and resulting CVI was radio frequency interference (RFI) produced when RM-11 sample pump seized. After the pump seized, the pump motor faulted and arced over to a bus ground.
The arcing produced sufficient RFI to induce the spurious high radiation signal. The design change to provide thermal overload protective circuitry for the sample pump motors the upgrade of the radiation monitoring system did not prevent the current LER.
C. Operating Experience Review:
- 1. NPRDS:
Not applicable.
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1 NCR DC1-92-TI-N020 Rev. 00 June 24, 1992
- 2. NRC Information Notices, Bulletins, Generic Letters:
A search of the Operating Experience Assessment database revteled the following:
None.
A search of the Operating Experience Assessment database revealed the following:
None.
D. Tr 7d Code:
Responsible department TI, and cause code C.4.
E. Corrective Action Tracking:
The tracking action request is A0264889.
F. Footnotes and Special Comments:
It was considered to replace the test boxes, but since the radiation monitors and system will be upgraded in the near future, the test boxes will no longer be needed, therefore no corrective action will be necessary. The inspection of the test boxes prior to use should ensure that there is no similar problem on the other test boxes.
G.
References:
- 1. Initiating Action Request A0264765.
- 2. Tracking Action Request A0264889.
- 3. Licensee Event Report (LER) 1-92-005-00.
- 4. Radiation monitor charts for 14 A&B and 28 A&B.
- 5. Personnel statements. i
- 6. Shift Foreman Log for April 28, 1992.
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l NCR DC1-92-TI-N020 Rev. 00 f June 24, 1992
- 7. Maintenance Bulletin dated June 20, 1992.
Subject:
CVI due to noise generated by degraded connector.
H. TRG Meeting Minutes:
On May 5, 1992, the TRG convened and considered the following:
- 1. Review of the event to determine the root cause. The root cause is unknown, but the theories which may have caused this event were discussed. It was postulated that the event may be due to:
- a. I&C technicians working on RM-28B severa.1 minutes before the CVI, but initially, no correlation could be made between their work and the spike on RM 14B.
- b. Scaffolding being erected at the time of the event and it was assumed that workers may have bumped the electrical panel. But after interviewing the workers it was that to deducted that they did not bump the panels nor done anything that would result in the signal experienced in the control room.
- c. Welding being performed in the area, which could have cc.;ed this event. 1&C will talk to plant safety (Paul Lucas) to check for outstanding welding permits.
- d. RM-28A and RM-14B share the same feeder breaker and the same power supply.
However, no evidence of AC power fluctuations was detected.
l 2. Several investigative actions were discussed and assigned.- They are as follows:
- a. Review the data from the PPC to determine any trend.
! RESPONSIBILITY: T. Eubank ECD: 5/19/92 DEPARTMENT: I&C Maintenance -
STATUS: COMPLETE.
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- w NCR DC1~92-TI-N020 Rev. 00 June 24, 1992
- b. Measure the DC and AC voltage.on the high l voltage power supply to determine if the measurements taken affected-the RM-28B or RM-14B count rate.
RESPONSIBILITY:_D. Weatherby ECD:- 05/19/82
- DEPARTMENT: I&C Maintenance
- c. ' Investigate if there are'any common conduits or raceway on' signal or high-voltage lines.
RESPONSIBILITY: D. Weatherby ECD:05/19/82 DEPARTMENT: I&C Maintenance
- d. An inspection of the_ external cabling on-top of the cabinets was done by'I&C, but no damage was noted.
l
- e. An investigation is being conducted to determine if noise could have been the cause for the abnormal signal output-experienced by RM-14B.
TRG TO RECONVENE ON MAY 26, 1992'TO REVIEW'THE RESULTS-OF THE INVESTIGATIVE-ACTIONS AND IF POSSIBLE DETERMINE THE ROOT CAUSE AND CORRECTIVE ACTIONS. i The TRG reconvened on May 26, 1992, to review the !
results of investigative actions. Subsequent to '
the last meeting of~the TRG,.I&C technicians j discovered c loose' connection in the test box being used on RM-28B at the time of the event. l l
This test box is used for test on RM-14'and RM-28 ;
only. This discovery-along with'a similar l occurrence due to a loose connection on the test box for a-different radiation monitor and the fact j that the technicians had started work on-RM-28B ;
only a few minutes before RM-14B went into alarm! l provides strong circumstantial evidence that this event was caused by. electronic noise created by the loose connection in the' test box.
A review of the signals-received prior to-and: !
during the event indicates'that_they.were not caused by a one time jar.or bump. This~ review in conjunction with-interviews of.the personnel working with the scaffolding: indicates.that this 92NCRWP\92TINO20.PGD .Page- 12. of 15
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i 2' NCR DC1-92-TI-N020 Rev. 00 l June 24, 1992 l
i event was not caused by the personnel erecting the scaffolding.
A review of the-welding records indicates.that no welding was being performed.anywhere in the area at the time immediately before or during the event.
An attempt to recreate the problem was unsuccessful.
The test boxes maybe scheduled for' replacement in 1993.
The TRG will reconvene. June 4, 1992, to determine applicable corrective actions to preclude-recurrence. LER 1-92-005-00'will be revised-to report the root cause and applicable corrective actions. An AE for the LER will be issued ~at-the same time the AEs'are issued for the new- ,
corrective actions.
On June 4, 1992 the TRG reconvened to discuss the root cause and corrective actions.
It was pointed out that the signa 1Lcables have a common conduit, but the conduit had no' bearing on.
the noise generated since the cables are' shielded.
The location of the test box in front of.the drawer may have contributed to the generation of the RF noise in RM-14B.
A review of the event and possible causes was. )
conducted.
l The next week end after'the event,.during similar testing on Unit 2 some elevated' readings were )
noted. The'I&C technician performing the work i suspected a problem with the test box and-subsequently discovered the' degraded' connector j termination. 4 The I&C technicians were-using the same test-box-around.the time that the event. happened, providing a I
~
circumstantial evidence that the cause of the event was related to the work being performed with 1
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i NCR DCl-92-TI-N020 Rev. 00 June 24, 1992 the test box. The loose connector.in the test box may have caused the spurious signal that resulted in the alarm. It has been established that it is not a personal error.
It was considered to replace the test boxes, but since the radiation monitors and system will be upgraded in the near future, the test boxes will no longer be needed. Therefore, no corrective ,
action will be necessary. The inspection on the l other test boxes used, should ensure that no' similar problems exist.
I&C will determine when the radiation monitors are to be replaced during the system upgrade project.
It was determined that the faulty test box connector could cause elevated readings on the radiation monitors.
The following corrective actions to prevent recurrence were established: _
- 1. Write an I&C maintenance bulletin to cover the event and precautions to take during similar-maintenance activities. Although the I&C technicians are aware of that, nced to warn them to keep the test box away.from the drawers.
- 2. Upon completion and approval of the maintenance bulletin submit a Training Improvement Proposal (TIP) to be included'in the I&C quarterly maintenance seminar. The action will be considered complete when the TIP number is issued.
J. Include a discussion on radiation monitors in a tailboard to cover the event and precautions to take during similar maintenance activities.
- 4. I&C technicians will make a one time visual inspection of other test boxes to ensure that there are no similar problems with the other test boxes and assocjated connectors.
- 5. The TRG to reconvene to sign the NCR, after the LER is sent.
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- 6. Send the NCR to the-PSRC. l 4
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- 7. . Closure of the NCR', ECD:- August 3 0 , .,1 9 9 2 .
l I. Remarks:
None.-
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