05000482/LER-2014-004, Regarding Condition Prohibited by Technical Specifications Due to an Instrument Tunnel Sump Level Indication Transmitter Incompatible with the Containment Environment
| ML14224A015 | |
| Person / Time | |
|---|---|
| Site: | Wolf Creek  |
| Issue date: | 07/31/2014 |
| From: | Rich Smith Wolf Creek |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| WO 14-0062 LER 14-004-00 | |
| Download: ML14224A015 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(viii)(B) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(ix)(A) 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 4822014004R00 - NRC Website | |
text
W* oLF CREEK NUCLEAR OPERATING CORPORATION Russell A. Smith Site Vice President July 31, 2014 WO 14-0062 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555
Subject:
Docket No.
50-482:
Licensee Event Report 2014-004-00, "Condition Prohibited by Technical Specifications due to an Instrument Tunnel Sump Level Indication Transmitter Incompatible with the Containment Environment" Gentlemen:
The enclosed Licensee Event Report (LER) 2014-004-00 is being submitted pursuant to 10 CFR 50.73(a)(2)(i)(B) regarding an operation or condition prohibited by Technical Specifications.
This letter contains no regulatory commitments. If you have any questions concerning this matter, please contact me at (620) 364-4156, or Mr. Steven R. Koenig at (620) 364-4041.
Sincerely, Russell A. Smith RAS/rlt Enclosure cc:
M. L. Dapas (NRC), w/e C. F. Lyon (NRC), w/e N. F. O'Keefe (NRC), w/e Senior Resident Inspector (NRC), w/e
~-
P.O. Box 411 / Burlington, KS 66839 / Phone: (620) 364-8831 An Equal Opportunity Employer M/F/HCNET
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 01/3112017 (01-2014)
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- 3. PAGE WOLF CREEK GENERATING STATION 05000 482 1 OF 4
- 4. TITLE Condition Prohibited by Technical Specifications due to an Instrument Tunnel Sump Level Indication Transmitter Incompatible with the Containment Environment
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED MONTH DAY YEAR YEAR SEQUENTIAL REV FACILITY NAME DOCKET NUMBER NUMBER NO.
MONTH DAY YEAR 05000 06 02 2014 2014 -
004 00 07 31 2014 FACILITY NAME DOCKET NUMBER 05000
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)
D 20.2201(b) 20.2203(a)(3)(i) 50.73(a)(2)(i)(C)
[] 50.73(a)(2)(vii) 1L 20.2201(d)
L 20.2203(a)(3)(ii)
[I 50.73(a)(2)(ii)(A) 50.73(a)(2)(viii)(A)
L 20.2203(a)(1)
LI 20.2203(a)(4)
L 50.73(a)(2)(ii)(B)
L 50.73(a)(2)(viii)(B)
LI 20.2203(a)(2)(i)
Li 50.36(c)(1)(i)(A)
LI 50.73(a)(2)(iii)
LI 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL L
20.2203(a)(2)(ii)
LI 50.36(c)(1)(ii)(A)
L 50.73(a)(2)(iv)(A)
L 50.73(a)(2)(x)
LI 20.2203(a)(2)(iii)
L 50.36(c)(2)
Li 50.73(a)(2)(v)(A)
LI 73.71(a)(4) 100 l 20.2203(a)(2)(iv)
L[j 50.46(a)(3)(ii)
L] 50.73(a)(2)(v)(B)
L_
73.71 (a)(5)
LF20.2203(a)(2)(v)
Li 50.73(a)(2)(i)(A)
Lj 50.73(a)(2)(v)(C)
LJ OTHER 20.2203(a)(2)(vi)
[XI 50.73(a)(2)(i)(B)
Lj 50.73(a)(2)(v)(D)
Specify in Abstract below or in I
PLANT CONDITIONS PRIOR TO THE EVENT Mode - 1 Power-100%
There were no systems, structures or components (SSC) that were inoperable at the start of the event and contributed to the event.
BACKGROUND The instrument tunnel sump level transmitter [EIIS Code: IJ, LIT] (LFLT0079) is part of the dirty radwaste drain subsystem [EIIS Code: WD] of the Floor and Equipment Drain System [EIIS Code: WK]. The instrument tunnel sump is part of the Containment Sump Level and Flow Monitoring System. This system detects a leak in the Reactor Coolant System [EIIS Code: AB] (RCS) by level changes in the containment normal or instrument tunnel sumps [EIIS Code: IJ]. Indication of increasing sump level is transmitted from the sump to the control room level indicator by means of a sump level transmitter. The system provides measurements of low leakages by monitoring level increase versus time.
DESCRIPTION
On May 28, 2014 Control Room operators noted that the instrument tunnel sump unidentified leak rate computer point was coming in and out of alarm high. On May 28, 2014 at 2130 Central Daylight Time (CDT), operations declared the instrument tunnel sump level indication inoperable. Condition A of Limiting Condition for Operation (LCO) 3.4.15, "RCS Leakage Detection Instrumentation," was entered for the inoperable Containment Sump Level and Flow Monitoring System. Condition A requires an RCS water inventory balance, Surveillance Requirement (SR) 3.4.13.1, be performed once per 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> and restoration of the Containment Sump Level and Flow Monitoring System to operable status in 30 days.
Investigation found that the instrument tunnel sump level indication had become erratic at approximately 1800 CDT on May 21, 2014. Further review of the computer point identified that the level transmitter had "locked up" and produced a constant output signal. This lock up condition was observed on May 22, 2014 and during a few months in 2013. During this time frame from July 13 to November 20, 2013, the level transmitter stopped its downward trend of evaporation and appeared to be locked up. On November 20, 2013, the level transmitter output signal dropped from about 10.2 inches to about 5.2 inches in 2 seconds.
The sudden drop suggests that either the level transmitter was mechanically bound or in lock out condition.
The current level transmitter model was installed in March 2013 and is a digital level transmitter. The previous transmitter model was used between 2000 and 2013 and was an analog design.
The factors and potential causes for the erratic signal and the potential lock up condition were broken down into the mechanical and electrical areas by Engineering. The level transmitter's vendor indicated that possible component degradation within the transmitter was causing the erratic behavior in output signal. One of the most likely causes for this degradation is radiation exposure of which the installed level transmitter has no qualification.
The vendor has exposed similar level transmitter models to less than 30,000 Rads and has experienced no failures. When exposed from 30,000 to 80,000 Rads, intermittent failures were observed and above 80,000 Rads failure occurred. The current level transmitter was installed in March of 2013 and, using a dose estimate of 5 Rem/hr gamma, has been exposed to at least 30,000 Rads.
The lock up experienced from July 13 to November 20, 2013 was likely caused by the level transmitter's software; when a faulted condition is experienced, the transmitter defaults to a failsafe mode. In the failsafe condition, the level transmitter defaults to the last reading. The lock up observed on May 22, 2014 was confirmed to be the result of a fault.
Compensatory measures were taken to maintain the capability of the instrument tunnel sump level indication to perform its specified function. These measures involve introducing water at a known rate into the instrument tunnel sump by a temporary modification and averaging the instrument tunnel sump level over a 60 second interval for input into the RCS leak detection program. On June 7, 2014 at 1529 CDT, the instrument tunnel sump level indication was declared operable but degraded and Condition A of LCO 3.4.15 was exited.
REPORTABILITY
Technical Specification (TS) LCO 3.4.15 requires the Containment Sump Level and Flow Monitoring System to be operable in Modes 1, 2, 3, and 4. Condition A of LCO 3.4.15 requires an RCS water inventory balance, SR 3.4.13.1, be performed once per 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> and restoration of the Containment Sump Level and Flow Monitoring System to operable status in 30 days. If SR 3.4.13.1 is not performed once per 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> or the Containment Sump Level and Flow Monitoring System not restored to operable status within 30 days, Condition E is also entered. Condition E requires the unit be in Mode 3 in 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and Mode 5 in 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />. The Containment Sump Level and Flow Monitoring System was inoperable from July 13, 2013 until November 20, 2013. The discovery date for this inoperability was June 2, 2014.
This exceeded the Completion Times of the Required Actions of Condition A and Condition E for LCO 3.4.15 and is therefore reportable as a condition prohibited by TS per 10 CFR 50.73(a)(2)(i)(B).
CAUSE
The apparent cause is the digital level transmitter design is not suitable for the instrument tunnel sump application. The most likely cause of the erratic output signal of the level transmitter is electrical in nature and is component degradation within the transmitter. The vendor has exposed similar level transmitter models to less than 30,000 Rads and has not experienced any failures. When exposed to 30,000 to 80,000 Rads intermittent failures were observed and above 80,000 Rads failure occurred. The current level transmitter was installed in March of 2013 and, using a dose estimate of 5 Rem/hr gamma, has been exposed to at least 30,000 Rads.
CORRECTIVE ACTIONS
After the erratic behavior of the instrument tunnel sump level transmitter was identified on May 28, 2014, the instrument tunnel sump level indication was declared inoperable and Condition A of LCO 3.4.15 was entered.
Compensatory measures were taken to maintain the capability of the instrument tunnel sump level indication to perform its specified function. These measures involve introducing water at a known rate into the instrument tunnel sump by a temporary modification and averaging the instrument tunnel sump level over a 60 second interval for input into the RCS leak detection program.
Restoration of the instrument tunnel sump level transmitter from the degraded condition is being accomplished under the corrective action program.
SAFETY SIGNIFICANCE
The actual nuclear safety significance of the instrument tunnel sump level indication is low. The level transmitter is a non-safety related component that is not required to mitigate the effects of a design basis accident or bring the plant to a safe shutdown condition.
The RCS Leakage Detection Instrumentation consists of the Containment Sump Level and Flow Monitoring System, one containment atmosphere particulate radioactivity monitor, and one Containment Air Cooler Condensate Monitoring System. One containment atmosphere particulate radioactivity monitor and one Containment Air Cooler Condensate Monitoring System were operable during this event. Also, the containment normal sump level indication was available.
OPERATING EXPERIENCE/PREVIOUS EVENTS None.