ML20059C726
| ML20059C726 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 08/19/1993 |
| From: | Rueger G PACIFIC GAS & ELECTRIC CO. |
| To: | |
| References | |
| OLA-2-I-MFP-087, OLA-2-I-MFP-87, NUDOCS 9401060046 | |
| Download: ML20059C726 (8) | |
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U April 20, 1992 PG&E Letter No. DCL-92-090 U.S. Nuclear Regulatory Commission ATTN:
Document Control Desk Washington, D.C.
20555 d' 0 %
Re:
Docket No. 50-323, OL-DPR-82 Diablo Canyon Unit 2 Licensee Event Report 2-91-010-01 TS 3.3.3.6 Action Limit for an Inoperable Reactor Cavity Sump Wide Range Level Channel Was Exceeded Due to inadequate Corrective Actions Following a 1990 Channel Failure Gentlemen:
Pursuant to 10 CFR 50.73(a)(2)(i)(B), PC&E is submitting the' enc'ased revision to Licensee Event Report (LER) 2-91-010-00 regarding an inoperable wide range reactor cavity sump level channel.
This revision is being submitted to report the results of PG&E's investigation into the root cause of the event and to report corrective actions that have been taken.
Revision bars are included to indicate the changes.
Sincerely,
[G ipt p GregbryM.Rueger cc:
Ann P. Hodgdon John B. Martin Philip J. Morrill Harry Rood CPUC i
Diablo Distribution INPO l
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LICENSEE EVENT REPORT (LER) 188618 1
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TS 3.3.3.6 ACTION LIMIT FOR AN INOPERABLE REACTOR CAVITY SUMP WIDE RANGE LEVEL CHANNEL ma i.i WAS EXCEEDED DUE TO INADEQUATE CORRECTIVE ACTIONS FOLLOWING A 1990 CHANNEL FAILURE Evimi DAT E 15 6 kmq mtmesAn see MEPORY DATE (7)
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On October 22, 1991, at 0958 PDT, with Unit 2 in Mode 2 (Startup) at 0 percent I
power, Action Statement a of Technical Specification (TS) 3.3.3.6 was exceeded due l
to reactor cavity sump wide range level' channel 942A being inoperable for greater than seven days in Modes 1 (Power Operation), 2, or 3 (Hot Standby).
Troubleshooting did not identify any equipment problems.
The channel was returned to service at approximately 1700 PDT.
The channel was declared operable ot 2115 PDT on October 22, 199], because the channel parameters were determined to be within allowable tolerances.
The failure to meet the TS Action Statement was caused by inadequate corrective actions for a prr.vious similar occurrence.
During investigative actions performed i
following a Mar.h 15, 1992, channel 942A f ailure, I&C discovered that only the 2ero range had been affected by the failure.
The channel was operable in all the ranges required for the performance of its intended safety functions.
It is now believed that the previous failures were similar; therefore, this channel was l
operable during these previous events.
STP l-1B was revised to require that the CSF-5 display screen of the Safety Parameter Display System (SPDS) be reviewed to identify problems with reactor l
cavity sump wide range level channels.
The transducer and the entire electronics package for channel 942A were replaced.
Nu subsequent failures have occurred.
Information plaques were installed on the SPDS display panels describing the SPDS signals for a channel problem.
Additional training has been provided to operators to increase sensitivity to these failures.
57385/85K
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I.
Plant Conditions Unit 2 was in Mode 2 (Startup) at 0 percent power during the Unit 2 fourth refueling outage.
II.
Description of Event A.
Event:
On October 22, 1991, at approximately 1500 PDT, an NRC inspector identified a question mark at the reactor cavity sump level channel input to critical safety function (CSF) display screen number 5 of~ the safety parameter display system (SPDS)(IP)(CSL).
The question mark is indicative of a problem with input Jata for one channel that monitors a given parameter. The inspector then examined the strip chart.
recorder (IP)(La) for reactor czvity sump wide r age level channel 942A (IP)(CHA). Channel 942A displays reactor cavity sump water level on the strip chart.
The inspector identified that channel 942A was out of tolerance. This problem was identified to the operators, and the channel was declared inoperable.
Instrumentation and Controls (l&C) technicians were requested to troubleshoot channel 942A, Troubleshooting efforts identified that channel 942A was approximately 1 millivolt (mV) out of tolerance low. This would indicate a water level approximately 10 inches below actual level.
During troubleshooting efforts, the channel modifier power fuses were removed for inspection. The fuses and level modifier were found to be operable. The modifier converts an input voltage signal to an output current signal.
After the moditier power fuses were reinstalled, channel parameters returned to normal.
On October 22, 1991, at approximately 1700 PDT, channel 942A was returned to service. At 2115 PDT, channel 942A was declared operable since troubleshooting did not identify any problems with the channel, and channel parameters were normal.
During subsequent examination of the strip chart, I&C noted that channel 942A had been out of tolerance since October 10, 1991.
Therefore, it was determined that channel 942A had been inoperable since October 10, 1991.
Technical Specification (TS) 3.3.3.6 requires that both reactor cavity sump wide range level channels be operable in Modes 1 (Power Operation), 2, and 3 (Hot Standby). TS 3.3.3.6.a requires that an inoperable channel be returned to service within seven days.
Since Unit 2 had entered Mode 3 on October 15, 1991 (at 0958 PDT) with the required channel 942A inoperable, the TS action statement should have been entered at that time. The action statement expired on October 22, 1991, at 0958 PDT. Therefore, it was determined that channel 942A 573RR / A5K
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,[ET (17) had been inoperable for more than seven days while Unit 2 was in Modes 2 and 3, contrary to TS 3.3.3.6.a.
The operators did not identify the inoperability of channel 942A during the performance of Surveillance Test Procedure (STP) 1-10
" Routine Monthly Checks Required by Licenses," or STP I-1B, " Routine.
Daily Checks Required by Licenses," that were perforned after October 10, 1991, because the diffe*ance between the normal indicated level on the recorder and the failed low indicated level is no more than 1/16 of an inch. One sixteenth of an inch is approximately the error that can be induced due to. chart paper alignment on the recorder.
B.
Inoperable Structures, Components, or Systems that Contributed to the Event:
Channel 942A was inoperable.
C.
Dates and Approximate Times for Major Occurrences:
1.
October 10, 1991:
Channel 942A drifted out of tolerance low.
2.
October 15, 1991, at 0958 PDT:
Unit entered Mode 3 and should have entered TS 3.3.3.6 Action
'i Statement a.
3.
October 22, 1991, at 0958 PDT:
Event date - Action Statement i
for TS 3.3.3.6.a expired.
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4.
Octooer 22, 1991, at 1500 PDT:
Discovery date - Channel 942A was ueclared inoperable.
j 5.
October 22, 1991, at 2115 PDT:
Channel 942A was declared operable.
D.
Other Systems or Secondary Functions Affected:
None.
E.
Method of Discovery:
The problem was identified to plant operators by an NRC inspector during a review of the SPDS system.
l F.
Operators Actions:
None.
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G.
Safety System Responses:
None.
III.
Cause of the Event A.
Imediate Cause:
The imediate cause of the violation of TS 3.3.3.6.a was the apparent l
failure of channel 942A.
B.
Root Cause:
1.
Failure to meet the 7-day Action Requirement of Technical Specification 3.3.3.6.
i The root cause for failing to meet the 7-day Action Rec,Jiremeht of Technical Specification 3.3.3.6 was inadequate carrective actions taken during a similar event in 1990.
The Technical Review Group (TRG) investigating the August 1990 containment wide range sump level channel 942A and 943A failures determined that since the blue flashing path had been identified during a control room routine daily surveillance (STP I-1B), the root cause of the failure to identify and correct the problem was a failure to understand the meaning of the blue flashing path on the SPDS display.
As corrective actions for the August 1990 event, the TRG required that applicable Operations and 1&C personnel receive training on the meaning of the blue flashing path. The TRG discussed the need to revise STP I-18, but incorrecy concludeu that the existing channel checks, in conjunction with additional training on the SPDS, would be sufficient to ensure equipment availability. The August 1990 event was reported in LER 2-90-010.
2.
Failure of Containment Sump Level Wide Range Transmitter.
During investigative actions performed following a March 15, 1992, channel 942A failure, 1&C discovered that the channel had not failed, but had experienced a zero shift.
It is now believed that this is what had happened during the past unexplained failures of this channel.
With the zero shift, only the zero reading was affected. Other levels indicated correctly; therefore, channel 942A was capable of performing its intended safety function.
57385/REV
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IV.
Analysis of theTint Containment reactor cavity sump wide range level channels are post-accident instrumentation (IP) required by Regulatory Guide 1.97 to provide quantitative data about water level inside the containment structure (NH) from the 64-foot elevation to the 98-foot elevation. These data are used to verify the occurrence of a loss-of-coolant accident (LOCA) and to evaluate plant conditions to assure proper response to an accident.
4 Using a combination of other instrumentation available as described below, the severity of an accident could be evaluated to determine the correct response.
Various annunciatcrs and indicators are available for identifying a LOCA.
l During a LOCA, containment pressure and temperature increase; reactor coolant system (AB) inventory decreases; and the containment reactor cavity sump level, containment structure sump level, and containment recirculation sump level increase.
The wide range pressure recorders (IK)(PR) record containment pressure.
The wide range temperature indicators (IK)(TI) are used to monitor containment temperature.
Reactor coolant system (RCS) inventory is monitored by pressurizer level indicators (AB)(PZR)(LI) and the reactor vessel wide range level r
indication system (IP). These indications could be used to diagnose the severity of an accident and assure that the core is adequately cooled.
Levels of the various sumps in the containment building are also monitored.
The narrow range containment structure sump level channels (IP)(CHA) indicate reactor cavity sump level from the 60-foot 4-inch elevation to the 63-foot 6-inch elevation. The residual heat removal recirculation sump indicators (BP)(LI) measure the residual heat removal recirculation sump level between the 88-foot elevation and the 96-foot 6-inch elevation.
A LOCA condition could be identified using the narrow range containment structure sump level channels.
Therefore, even if channel 942A was inoperable, a LOCA condition could be identified and properly responded to by using other instrumentation as described above.
Thus, the health and safety of the public was not affected by this event.
V.
Corrective Actions A.
Immediate Corrective Actions:
Troubleshooting was performed on channel 942A with no cause for the apparent failure identified.
The channel was declared operable and l
returned to service after a satisfactory channel check.
57385/BcK
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B.
Corrective Actions to Prevent Recurrence:
1.
Failure to meet the 7-day Action Requirement of TS 3.3.3.6.
STP I-1B was revised to require that the CSF-5 display a.
screen of the SPDS be reviewed to identify problems with reactor cavity sum' wide range level channels.
Since the p
revision of STP I-1B has been in effect, four channel failures have been detected and corrected without the ?-oay Action Statement of TS 3.3.3.6 being exceeded.
b.
Information plaques were installed on the SPDS display panels describing the SPD, signals for a channel problem.
S c.
Additional training has been provided to operators to incr ase sensitivity to these failures.
d.
A memo will be issued to applicable personnel describing this event and the importance of considering measures for monitoring equipment performance during the interim period prior to the completien of the root cause investigation.
These corrective actions are believed to be sufficient to prevent exceeding the 7-day Action Statement of TS 3.3.3.6.
2.
Failure of Containment Sump Level Wide Range Transmitter.
During investigative actions performed following a March 15, 1992, channel 942A failure, I&C discovered that only the zero range had been affected by the failure. The channel was operable in all the ranges required for the performance of its intended safety functions.
It is now believed that the previous failures i
were similar; therefore, this channel was operable during these previous events.
The transducer and the entire electronics package for channel 942A were replaced. No subsequent failures have occurred.
VI.
Additional Information A.
Failed Components:
Level Transmitter Manufacturer: Combustion Engineering Hodel Number: NQPT-2 57385/REV
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B.
Previous Similar Events:
LER 2-90-010-01 Inoperable Wide Range Containment Reactor Cavity Sump Level Channels On November 6, 1990, I&C technicians identified that reactor cavity sump wide range level channels 942A and 943A had been inoperable for more than 7 days in violat.. of TS 3.0.3.6.a.
The root cause of the failure of channel 943A was determined to be normal wear-out of the power supply fuse. The root cause for the failure of channel 942A could not be determined.
The corrective action for the event was to include the meaning of a blue flashing path on the SPDS CSF display screen in operator and I&C training.
A blue flashing path on the SPDS CSF display screen identifies invalid data input from all channels that monitor a given parameter.
The operator and I&C training also included the meaning of a question mark on the SPDS CSF display screen.
The recurrence of the violation of TS 3.3.3.6 a identified that the corrective action to train the operators was not adequate to prevent recurrence of the event.
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