IR 05000275/1994029
| ML16343A668 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 12/16/1994 |
| From: | Kirsch D NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| To: | |
| Shared Package | |
| ML16342C772 | List: |
| References | |
| 50-275-94-29, 50-323-94-29, NUDOCS 9412230086 | |
| Download: ML16343A668 (22) | |
Text
APPENDIX B U.S.
NUCLEAR REGULATORY COMMISSION
REGION IV
Inspection Report:
50-275/94-29 50-323/94-29 Licenses:
DPR-80 DPR-82 Licensee:
Pacific Gas and Electric Company 77 Beale Street, Room 1451 P.O.
Box 770000 San Francisco, California Facility Name:,
Diablo Canyon Nuclear Power Plant, Units 1 and
Inspection At:
Diablo Canyon Site, San Luis Obispo County, California Inspection Conducted:
November 1 through December 2,
1994 Inspector:
G. Johnston, Senior Project Inspector Approved:
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e Ins ection Summar Areas Ins ected Unit 2
A special inspection of the circumstances associated with three accumulators being below minimum Technical Specification (TS) limits for pressure on October 28, 1994.
During the inspection, Inspection Procedure 92901 was used.
Areas Ins ected Unit
No inspection of Unit I was performed.
pp1 On October 28, 1994, while Unit 2 was in MODE 1, Accumulators 2-2, 2-3, and 2-4 were determined to be below their minimum TS pressure limit of 595.5 psig.
This condition occurred as the result of an equipment control clearance that was improperly installed and verified.
The improper clearance resulted in inaccurate calibration of safety injection accumulator pressure channels during Refueling Outage 2R6.
Furthermore, the licensee's untimely evaluation of the Action Requests documenting as-found, out-of-calibration conditions on six instrument calibrations led directly to changing operating MODEs from MODE 4 through MODE 1 with three accumulators below the minimum pressure required by plant TS.
9412230086 94i2ih PDR ADOCN 05000275,
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Maintenance Weaknesses:
An equipment clearance was modified without obtaining prior review and approval.
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During the hanging of a clearance, the independent verification did not identify that the clearance had not been hung in accordance with the instructions of the clearance.
Plant 0 erations Weakness:
The lack of prioritization for the review of six Action Requests (AR),
each documenting a similar condition, resulted in an untimely evaluation of an out-of-tolerance condition involving six of eight safety injection accumulator pressure channels.
Consequently, Unit 2 was allowed to transition upward from MODEs 4 through 1, with three accumulators below the minimum pressure required by the plant TS.
Summar of Ins ection Findin s:
Violation 323/94-29-01 was identified (Section 2. 1).
Violation 323/94-29-02 was identified (Section 2.2).
Violation 323/94-29-03 was identified (Sections 2.3 and 2.4).
Attachments:
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Attachment
Persons Contacted and Exit Meeting
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Attachment
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DETAILS
BACKGROUND On October 28, 1994, while Unit 2 was in MODE 1, Accumulators 2-2, 2-3, and 2-4 were determined to be below their minimum TS pressure limit of 595.5 psig.
The Unit had reached MODE 1 that morning at 5:50 a.m., after completing Refueling Outage 2R6.
All trains of safety-related emergency core cooling system equipment were operable and available at that time.
During a morning meeting, on October 28, 1994, the Operations Department and Instrument and Controls Department had become, fully aware of a possible discrepancy involving the pressure instrumentation channels on three of the four accumulators.
A decision was made to open the nitrogen supply valves and allow the four accumulators to equalize in pressure to confirm that each of the three affected accumulators'wo pressure channels were operable.
It was believed at the time that the pressure channels on Accumulator 2-1 were unaffected and could be re1ied upon for proper indication.
After cross-connecting the nitrogen supply, Accumulators 2-2, 2-3, and 2-4 registered an increase in indicated pressure of from 5 to 13 psi, while Accumulator 2-1 decreased in pressure from 623 psig to 598 psig.
This demonstrated that Accumulators 2-2, 2-3, and 2-4 had been low in pressure.
It was later determined that, at the time of discovery, the three affected accumulators were from 5 to 9 psi below the TS limit of 595.5 psig.
The operators immediately initiated a pressurization of the accumulators to recover from the entry into TS 3.0.3.
The licensee then notified the NRC of the apparent inoperable status of the three accumulators in accordance with 10 CFR 50.72.
1. 1 Se uence of Events September 24, 1994 September 24, 1994 September 25, 1994 September 25, 1994 Sequence of Events Reactor shut down.
Accumulator 2-1 pressure channel calibrations for PT-960 and PT-961 performed.
Starting at 8:30 p.m., the calibrations were completed by the end of the shift.
Clearance 45351 hung on the Accumulator 2-1 pressure channel comparators at 10:51 a.m.
The other channels were tagged out within minutes in the same fashion.
Accumulators 2-2, 2-3, and 2-4 pressure channel calibrations completed over the next 2 day Au"
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fahrenheit, the licensee concluded their was no safety concern.
Because in the large-break LOCA RCS pressure rapidly decreases to that of the containment, the impact on the analysis of the reduced accumulator pressure on the PCT was determined to be neglible.
The NRC reviewed the licensee event report analysis and agreed with the licensee's conclusions.
Diablo Canyon TS 3.0.4 states, in part, that "Entry into an OPERATIONAL MODE or other specified condition shall not be made when the conditions for the Limiting Conditions for Operations are not met and the associated ACTION requires a Shutdown if they are not met within a specified time interval."
Unit 2 entered MODE 3 on October 24, 1994, at 2:41 p.m. with pressurizer pressure above 1000 psig.
Diablo Canyon TS 3.5. 1 states, in part,
"Each Reactor Coolant System accumulator shall be OPERABLE with:
d.
A nitrogen cover-pressure of between 595.5 psig and 647.5 psig."
This requirement is applicable in MODES 1, 2,
and 3 above 1000 psig pressurizer pressure.
The TS requires a shutdown if the Limiting Condition for Operation cannot be met.
On October 28, 1994, while Unit 2 was in MODE 1, and following transitions from MODE 4 to MODE 3, and MODE 3 to MODE 2, it was determined that the pressure in Accumulators 2-2, 2-3, and 2-4 were less than 595.5 psig.
These conditions represent a violation of the TS requirements (Violation 323/9429-01).
2.2 Clearance Ta in for Annunciator U
rade On September 25, 1994, members of the Operations Department and Instrument and Controls Department proceeded to implement Clearance 45351.
This clearance was to de-energize AC electric inputs to the main annunciator system to allow replacement of relays associated with the annunciator system upgrade.
The de-energization was to be accomplished by removing fuses in the output circuits of devices providing input to the annunciator panels.
Included in this clearance were circuit comparators for accumulator high and low pressure alarms.
This would have affected 16 comparator outputs, requiring the removal of 16 fuses.
The clearance required 144 separate actions, each with a specific tag.
Comparators PC-960 through PC-967 each had two tags issued:
one each for the high pressure and low pressure alarm inputs to the main annunciator panel.
During the hanging of the tags, the persons hanging the tags decided to remove the channel comparator internal power supply fuse rather than the two output fuses.
While this action provided the same level of personnel protection as removing the two output fuses, this was contrary to the requirements of the clearance.
The removing of the power supply fuses had a deleterious effect on the instrument channel calibrations that were performed while this clearance was in effect.
The actions of the personnel implementing Clearance 45351 violated the clearance by removing power supply fuses instead of the specified output fuses for Comparators PC-960 through PC-967.
The inspector noted that Clearance 45351, which required independent verification, did not assure that the tagging was performed correctly.
It appears that the person performing the verification did not question the tagging as it was performed.
Further, the tagging process required a
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i verification and accounting of the tags when they were removed, In neither case were questions raised as to the nature of where the tags were hung.
These improper independent verification activities represented a significant missed opportunity to have prevented the accumulator underpressure condition.
Procedure OP2. ID1,
"DCPP Clearance Process,"
describes in Section 5.9, the steps required to modify a clearance.
No action was taken to change the clearance in accordance with Section 5.9 of Procedure OP2. IDl.
The actions of the personnel constitute a failure to follow procedural requirements and are an example of a violation of TS 6.8. 1, which requires that written procedures shall be established, implemented, and maintained covering the applicable procedures recommended in Appendix A of Regulatory Guide 1.33, Revision 2,
including procedures covering the performance of clearances on safety related systems (Violation 323/9429-02).
Procedure OPI.DC2, "Verification of Operating Activities," describes in Section 4.4.4 the requirement for proper verification of the removal and installation of fuses.
This section states, in part,
"The position of circuit breakers, fuses, and switches shall be verified by observation of the device requiring independent verification
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Specifically, the procedure prescribes that
"Fuses shall be verified to be properly installed or removed."
During the performance of Clearance 45351, the independent verification did not identify that the clearance had not been implemented in accordance with the instructions of the clearance (i.e., the correct fuses had not been removed).
Further, no notice was made of the error when the tags were removed.
Again, the actions of the personnel verifying the clearance tags constituted a failure to follow procedural requirements and are a second example of a violation of TS 6.8. 1.
~ 1 requires that written procedures shall be established, implemented, and maintained covering the applicable procedures recommended in Appendix A of Regulatory Guide 1.33, Revision 2, including procedures covering the performance of clearances on safety related systems (Violation 323/9429-02).
The inspector noted that it was fortuitous that two channels of instrumentation were calibrated prior to the clearance error, thereby exposing the instrument calibrations to greater scrutiny.
Otherwise, it is possible that Unit 2 may have operated with four accumulators at less than the required pressure for a longer period than actually occurred.
2.3 Instrument Channel Calibrations On September 25-26, 1994, Instrument and Controls technicians performed instrument channel calibrations in accordance with Surveillance Test Procedure (STP)
1-9-P960.B through I-9-P967.B.
These are the TS required refueling interval accumulator pressure channel calibrations.
The instrument calibrations involve utilizing a water ram, a 0-1000 psi precision pressure gauge, and a digital multi-meter.
The multi-meter test point utilizes a
voltage measurement made across the test jacks of the signal comparator unit in the instrument loop.
The measurement determines the voltage drop across a
250 ohm resistor, a voltage that varies from 1 to 5 volts.
The test location
chosen ensured an overlap between the refueling interval calibration and the monthly channel functional test.
This overlap was required to allow crediting the monthly channel functional test, conducted on September 21, 1994, as a
portion of the refueling interval instrument calibration.
The affected channels (Accumulator Pressure Channels PT-962 through PT-967)
were calibrated during the period in which the channel comparator internal power supply fuse was removed for Clearance 45351.
Transmitters PT-960 and PT-961, for Accumulator 2-1, were calibrated before the clearance was implemented and, thus, were not affected by the removal of the power supply fuse.
The removal of the power supply fuse affected the impedance of the signal comparator.
The impedance would change from approximately a
Hohm value to approximately 2.5 Kohms when the fuse was removed.
The inspector observed a demonstration of this effect on a test bench mockup of the circuit.
The inspector observed on the circuit mockup the effect of a linear offset of from 4.6 to 4. 1 percent of scale over the range of 4 to 20 milliamps output of the pressure transmitter.
Consequently, the technicians had observed an as-found, out-of-tolerance condition, at the beginning of the calibration, analogous to 25 psi to 28 psi at a nominal accumulator pressure of 615 to 625 psig.
Following,the first instance of an out-of-tolerance condition, the technicians conducted an investigation.
The reason stated for this investigation was that they had not experienced this situation before.
Normally, the technicians noted, the channels are an "as-found, as-left" =verification, with an occasional adjustment for drift.
However, with six of the eight pressure channels having exhibited out-of-tolerances of more than 4 percent, the technicians questioned the results.
The investigation included checking the test equipment, verifying the test setup was as required, and utilizing another test method to validate the results.
With no apparent problems identified, the technicians adjusted the pressure transmitters to achieve what was thought at the time to be correct pressures.
The technicians'oreman then issued out-of-tolerance ARs, that are required whenever surveillance test results do not meet the acceptance criteria.
CFR Part 50, Appendix B, Criterion V, specifies that activities affecting quality be prescribed by documented procedures of a type appropriate to the circumstances.
The inspector determined that the STPs used to calibrate the accumulator pressure instruments (STP I-9-P960.B through I-9-P967.B)
on September 25-26, 1994, did not specify appropriate initial test condition requirements to ensure that the pressure instrument calibration was not adversely impacted by other maintenance activities.
This is an example of a violation of 10 CFR Part 50, Appendix B, Criterion V, for inadequate procedures (Violation 323/9429-03).
2.4 Corrective Actions The out-of-tolerance ARs were routed to the STP coordinator for review and analysis.
Procedure ON7. IDI, "Problem Identification and Resolution Action Requests,"
Section 4.5. 1, requires that these ARs be reviewed within 30 days
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of issuance.
The ARs were issued on September 26, 1994, and the reviewer commenced his review on October 24, 1994, which was within the 30-day window.
The procedure does not provide for prioritization of ARs for review, except for the case when a nonconformance report is generated.
A nonconformance report was not generated prior to the underpressure condition being verified on October 28, 1994; therefore, the six ARs were not prioritized.
The indication of six of eight safety-related instrument channels that were apparently out of calibration represents a significant anomalous condition deserving a detailed evaluation.
The lack of prioritization for the review of these ARs represents a failure to conduct sufficiently timely reviews of reported problems to support restart from short duration refueling outages.
The short length of Refueling Outage 2R6, 34 days, clearly indicates the necessity of prioritizing, for timely review, those ARs that involve questions of operability.
The inspector determined that Procedure ON7. IDI is inadequate in this regard.
A short outage should require that the review process for ARs that could affect operability be completed prior to the commencement of NODE changes.
Had the review been done in a timely manner, it may have provided a
barrier to the eventual underpressure condition of the accumulators.
The press of completing outage activities was stated as the reason for waiting until the end of the 30-day period.
The STP coordinator who conducted the review initially noted that it appeared the apparent out-of-tolerance condition of the accumulators may have been a
condition present during the last fuel cycle.
The concern was that the accumulator pressure may have been above the TS limit of 647.5 psig.
Consequently, the reviewer issued an AR to initiate an inquiry.
This inquiry started on October 25, 1994, while the plant was in NODE 3 above 1000 psig, where the TS 3.5. 1 requires that all four accumulators be operable.
The inquiry proceeded over the next 3 days.
During this interval, the plant entered MODE 2 on October 26, 1994, at 7:50 p.m.
and MODE
on October 28, 1994, at 5:50 a.m.
The MODE transitions occurred after the evaluation of the out-of-tolerance conditions were brought to supervisory attention.
The focus of the inquiry was toward the potential of having violated the high pressure limit in the TS during the preceding fuel cycle.
However, there was sufficient information available at the time to indicate that a problem may have existed at that time with the calibration of the six affected pressure channels.
The inspector concluded that the available information should have been enough to question the operability of the affected accumulators and cause a termination of the restart process.
This lack of a more questioning attitude represented another missed opportunity to prevent the accumulator underpressure condition.
Procedure ON7. IDI, "Problem Identification and Resolution Action Requests,"
did not provide instructions to appropriately address the circumstances associated with the accumulator pressures being below TS limits.
CFR Part 50, Appendix B, Criterion V, specifies that activities affecting quality shall be prescribed by documented instructions, procedures, or drawings, of a type appropriate to the circumstances.
On September 26, 1994, six ARs
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associated with the accumulator pressures were issued.
Section 4.5. 1 of the procedure requires that ARs be reviewed within 30 days of issuance; thus allowing the evaluation to be completed by October 26, 1994.
Licensee operators allowed the unit to enter MODE 3 on October 24, 1994.
Entry into HOOf 3 requires that all of the accumulators be operable.
For this case, Procedure OH7. 101 was inappropriate to the circumstances in that it allowed the evaluation, which would have determined operability of the accumulators, to be delayed until after entry into MODE 3 (Violation 323/9429-03).
ATTACHMENT 1
PERSONS CONTACTED l. 1 Licensee Personnel
- W.
- R.
- B
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H. Fujimoto, Vice President and Plant Manager, Diablo Canyon Operations P.
Powers, Manager, Nuclear equality Services Giffin, Manager, Maintenance Services Chaloupka, STP Coordinator L. Grebel, Supervisor Regulatory Compliance A. Hubbard, Engineer, Regulatory Compliance B. Miklush, Manager, Operations Services Nowlen, Senior IEC Engineer Philips, Director, Instruments and Controls C. Washington, Senior ILC Engineer Taggart, Director, Nuclear equality Services SgA Fridley, Director, Operations 1.2 NRC Personnel
- G. Johnston, Senior Project Inspector
- M. Tschiltz, Resident Inspector
- Denotes those attending the exit meeting November 4, 1994.
A telephone conference call exit meeting was held with members of the licensee's staff, on December 2,
1994, denoted by the '+'ymbol.
In addition to the personnel listed above, the inspector contacted other personnel during this inspection period.
EXIT MEETINGS Exit meetings were conducted on November 4 and December 2,
1994.
During these meetings, the inspector reviewed the scope and findings of the report.
The licensee acknowledged the inspection findings documented in this report.
The licensee did not identify as proprietary any information provided to, or reviewed by, the inspector flP
ATTACHHENT 2 ACRONYHS AR Kohm KV LOCA Hohm psl psig TS STP Action Request Kilo-ohm Kilo-volt loss-of-coolant accident Hega-ohm pounds per square inch pounds per square inch gauge Technical Specification surveillance test procedure
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