ML20059C708
| ML20059C708 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 08/19/1993 |
| From: | Shiffer J PACIFIC GAS & ELECTRIC CO. |
| To: | |
| References | |
| OLA-2-I-MFP-085, OLA-2-I-MFP-85, OLA-I-MFP-85, NUDOCS 9401060039 | |
| Download: ML20059C708 (7) | |
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September 16, 1991
'93 F 28 :' 10 PG&E Letter No. DCL-91-222 U.S. Nuclear Regulatory Commission ATTH:
Document Control Desk Washington, D.C.
20555 Re:
Docket No. 50-323, OL-DPR-82 Diablo Caryon Unit 2 Licensee Event Report 2-91-004-00 Technical Specification 3.4.6.2, Action b., Not Performed On Time Due To Calculation Error In A Surveillance Test Result Caused By Personnel Error i
Gentlemen:
Pursuant to 10 CFR 53.73(a)(2)(i)(B), PG&E is submitting the enclosed Licensee Event Report (LER) concerning a failure to meet Technical Specification 3.4.6.2., Action b., due to a calculation error in a surveillance test caused by personnel error.
This event has in no way affected the health and safety of the public.
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I On August 13, 1991, at 1700 PDT, Technical Specification (TS) 3.4.6.2 was not met when the Unit 2 Reactor Coolant System (RCS) unidentified leakage exceeded one gpm.
The required action, to reduce the unidentified leakage to the acceptable limit within four hours or be in Hot Standby within the next six hours, was not performed due to an error in a calcdation in Surveillance Test Procedure (STP) R-10C, " Reactor Coolant System Water Inventory Balance."
This STP had been completed 10 hours1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br /> earlier and had incorrectly salculated the unidentified l
leakage as less than one gpm.
i on August 13, 1991, at 1755 PDT, containment sump in-leakage was determined to be 1.2 gpm.
STP R-10C was performed and RCS unidentified leakage was determined to be 1.9 gpm. An Unusual Ever '. (UE) was declared.
Investigation identified the area where the leakage was occurring.
Isolation of that piping reduced the RCS unidentified leakage to 0.8 gpm.
On August 14, 1991, at 0019 PDT, the UE was terminated.
On August 16, 1991 it was determined that a calculation error had occurred for STP R-10C performed on August 13, 1991, at 0700 PDT. As a result, unidentified leakage had been approximately 1.4 gpm versus the 0.8 gpm recorded.
The root cause of this event was personnel error.
The personnel involved in this event have been counseled regarding the need for attention to detail and self verification.
5475S/0085K
LICENSEE EVENT REPORT (LER) TEXT CONTINUATION 177393 u.g.,
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Plant Conditions Unit 2 was in Mode 1 (Power Operation) at 99% power.
11.
Description of Event I
A.
Event:
On August 13, 1991, at 0700 PDT, Surveillance Test Procedure (STP) R-10C, " Reactor Coolant System Water Inventory Balance," was performed.
The data collected had a calculated unidentified leakage rate of 0.8 gallons per minute (gpm).
On August 13,1991, at 1755 PDT, STP R-10A/B, " Reactor Coolant System Leakage Evaluation," was performed.
STP R-10A/B determined containment sump unidentified in-leakage to be 1.2 gpm.
Action statement b. of Technical Specification (TS) 3.4.6.2 was entered.
On August 13, 1991, at 2010 PDT, STP R-10C was performed and determined that Reactor Coolant System (RCS)(AB) unidentified leakage was 1.9 gpm.
Excess letdown was isolated to determine if it was the source of the unidentified leakage.
There was no change in the unidentified leakage rate.
Excess letdown was returned to service.
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On August 13, 1991, at 2155 PDT, an Unusual Event (UE) was declared by Operations to inform management and the appropriate agencies of the Unit 2 condition.
i On August 13,1991, at 2200 PDT, Abnormal Procedure AP-17, " Loss of j
Charging," was entered. The charging header was isolated to determine j
if it was the source of the unidentified leakage.
Visual inspection observed that the leakage stopped.
STP R-10C was performed.
On August 14,1991, at 0019 PDT, the results of STP R-100 showed RCS unidentified leakage to be less than 1.0 gpm.
Thus, it was confirmed that the unidentified leakage path originated in the charging subsystem of the Chemical Volume Control System (CVCS)(CB). With the i
leakage below the TS limit, conformance with TS 3.4.6.2 action b. was achieved and the UE was terminated.
On August 16, 1991, engineers reviewing STP R-10C test results determined that a mathematical error had been made in the August 13, 1991, 0700 PDT unidentified leakage calculation.
The corrected calculation showed unidentified leakage as 1.4 gpm.
On August 20, 1991, a Technical Review Group (TRG) met and determined that, on August 13, 1991, at 1700 PDT, the Limiting Condition for Operation (LCO) of TS 3.4.6.2, Action b., was inadvertently exceeded when no action was taken to mitigate the RCS unidentified leakage rate
- 4755/0085K
LICENSEE EVENT REPORT (LER) TEXT CONTINUATION 177393 -
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B.
Inoperable Structures, Components, or Systems that Contributed to the Event:
None.
C.
Dates and Approximate Times for Major Occurrences:
1.
August 13, 1991; 0700 PDT:
STP R-10C performed with error and determined RCS unidentified leakage of 0.8 gpm.
2.
August 13, 1991; 1700 PDT:
Event date.
LCO inadvertently exceeded when undiscovered leak rate > 1.0 gpm not mitigated and Unit 2 not placed in Hot Standby.
3.
August 13, 1991; 1755 PDI:
STP R-10A/B was performed and showed an unidentified in-leakage rate of 1.2 gpm to the containment sump.
4.
August 13, 1991, 2010 PDT:
STP R-10C performed and showed actual leakage of 1.9 gpm.
5.
August 13, 1991; 2155 PDT:
UE was declared when RCS leakage wLs not controlled < 1.0 gpm.
6.
August 14, 1991; 0019 PDT:
Leak controlled below TS limit.
UE terminated.
7.
August 16, 1991:
STP R-10C from August 13, 1991, 0700 PDT found to have a calculation error.
Unidentified leakage was 1.4 gpm, not 0.8 gpm.
8.
August 20, 1991; 1100 PDT:
Discovery date. A Technical Review Group (TRG) met and determined that TS 3.4.6.2, Action b., had been exceeded.
D.
Other Systems or Secondary functions Affected:
None.
i 5475S/0085K
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Method of Discovery:
On August 16, 1991, engineers reviewing STP R-10C test results determined that an error had been made in an unidentified leakage calculation.
The calculation done for the August 13, 1991, 0700 PDT test recorded a leak rate of 0.8 gpm.
This calculation was found to have an error.
A TRG convened on August 20, 1991 to review this event for reportability.
It was determined that records show that unidentified RCS leakage exceeded 1.0 gpm on or before August 13, 1991 at 0700 PDT, and action was not taken to reduce the unidentified leakage rate within four hours or be in Hot Standby within the next six hours.
Thus, the LCO in TS 3.4.6.2, Action b., was exceeded.
F.
Operators Action!:
Operations isolated charging by closing valve CVCS-2-8146 to mitigate the leak.
G.
Safety System Responses:
None required.
III.
Cause of the Event A.
Immediate Cause:
The immediate cause of this event was a leak in the charging header.
B.
Root Cause:
The root cause of violating the LC0 for TS 3.4.6.2, Action b.,
was personnel error due to inattention to detail and a lack of self verification by the operator performing STP R-10C calculations.
C.
Contributory Cause:
Other shif t personnel who reviewed and approved the STP results did not perform an adequate verification in accordance with Administrative Procedure A-56, " Signatures and Signature Responsibility."
IV.
Analysis of the Event i
The inadvertent violation of TS 3.4.6.2 resulted from a calculation error f
during the performance of STP R-10C on August 13, 1991 at 0700 PDT. When the leak rate was observed to exceed the TS limit at 1755 PDT on the same day, appropriate investigative actions were performed to identify the source i
and mitioate the leakage.
J4755/0085K
LICENSEE EVENT REPORT (LER) TEXT CONTINUATION 177393 F A4]L]f f hAMt (3)
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On September 2, 1991, following orderly shutdown of Unit 2 on August 31, 1991, the lagging was removed from the normal charging line in the vicinity of the charging line check valves and the leak site was located.
The leak location site was observed to be in the body to bonnet gasket on the charging line check valve closest (first-off) to the RCS, CVCS-2-8378B l
(CB)(V).
A body to bonnet gasket leak is typically s.nall and, once initiated, increases gradually with time.
This characteristic was apparent with this leak.
PG&E considers the body to bonnet gasket leakage would not have produced an abrupt release of reactor coolant.
This evaluation is supported by EPRI Report No. NP-5769, April 1988.
This EPRI technical program analyzed various primary pressure boundary closures, including check valves.
Pressure boundary bolting integrity had the highest priority in the EPRI program.
Based on the EPRI results, reactor coolant pressure boundary joint degradation was determined not to be a safety issue.
Therefore, the body to bonnet gasket leak does not generate significant safety concerns due to rapid RCS depressurization and impact on core cooling.
Ample time is available to detect leakage, evaluate it, and take the proper and prudent compensating action.
The leakage rate was carefully monitored and the rate of increase was evaluated by the trend of the results of STP R-10C.
When the detected leak rate did exceed TS limits, appropriate actions were taken to mitigate the leak rate.
All leakage was contained within the Unit 2 containment.
No radioactive materials were released to the environment.
Thus, the health and safety of the public were not adversely affected by this event.
V.
Correttive Actions A.
Immediate Corrective Actions:
1.
Charging was isolated by closing valve CVCS-2-8146 to mitigate the leak.
l 2.
The frequency of RCS inventory measurements was increased from the TS requirement of once every 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />, to once every four hours.
3.
On September 2,1991, following orderly shutdown of Unit 2 on August 31, 1991, the lagging was removed from the normal charging line in the vicinity of the charging line check valves and the leak site was located.
The leak location site was determined to be the body to bonnet gasket on the charging line check valve closest (first-off) to the RCS, CVCS-2-8378B.
I 54755/0085K
LICENSEE EVENT REPCMT (LER) TEXT CONTINUATION 177393
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Corrective Actions to Prevent Recurrence:
The personnel involved were counseled on the need for attention to detail and self verification.
VI.
Additional Informatiorl A.
Failed Components:
Valve CVCS-2-8378B, 3", Velan, model 3C58.
B.
Previous LERs on Similar Events:
None.
54755/C085K
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