05000331/LER-2013-004
| Duane Arnold Energy Center | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3312013004R00 - NRC Website | |
I. Description of Event:
On December 23, 2012, while operating at 100% power, Temperature Indicating Switch (TIS) 4479 Channel 1, Turbine Building Main Steam Line 'C', was found indicating 183F. This indication did not meet the acceptance criteria of > 70F and Instrument Checks. Subsequently, the indicated temperature returned to within its acceptance criteria and no actions were taken to declare TIS-4479 inoperable. On December 28, 2012, TIS-4479, Channel 1 was again found to be outside of its surveillance requirements and was declared inoperable. A Past Operability Review (POR), completed on March 12, 2013, concluded that TIS-4479 was operable from December 23, 2012 to December 28, 2012. The POR conclusion was based on a lack of firm evidence indicating when the TIS was no longer performing its required safety function. A subsequent revision to the POR, completed on October 18, 2013, determined that TIS-4479 was inoperable from December 23, 2013 to December 28, 2012. Technical Specification (TS) 3.3.6.1, Primary Containment Isolation Instrumentation, Required Action D.1, requires the associated Main Steam Line to be isolated within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> or be in Mode 3 within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. Neither of these Required Actions were completed. Therefore, this condition constituted a condition prohibited by TS.
There were no other structures, systems or components inoperable at the start of this event that contributed to the event.
II. Assessment of Safety Consequences:
The safety significance of this event is low based on the fact that the other 7 Main Steam Line Isolation Channels were operable during the time TIS-4479 was inoperable.
Technical Specification (TS) 3.3.6.1, Primary Containment Isolation Instrumentation, Required Action D.1, requires the associated Main Steam Line to be isolated within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> or be in Mode 3 within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. Neither of these Required Actions were completed. Therefore, this condition constituted a condition prohibited by TS and is reportable to the NRC pursuant to 10CFR50.73(a)(2)(i)(B).
This event did not result in a safety system functional failure.
III. Cause of Event:
A Root Cause Evaluation was completed. The evaluation identified the following root causes of this event.
Root Cause 1 — An undetermined failure internal to the TIS affected its ability to provide accurate temperature indications.
Root Cause 2 — Procedural guidance of STP 3.0.0.0-01, Instrument Checks, did not include a requirement to perform a qualitative channel check as required by TS.
IV. Corrective Actions:
On December 29, 2012, TIS-4479 was replaced and returned to service.
In order to address the root cause of this event, the following corrective actions will occur.
A modification will be developed and implemented to replace the current Chromlox TIS with Yokogawa Recorders or other suitable instruments.
STP 3.0.0-01, Instrument Checks, will be revised to clearly state that a qualitative assessment of instrument performance should be performed for ANY instrument included in the STP that is being assessed to meet its CHANNEL CHECK surveillance requirement, not just for cases when the specified quantitative assessment cannot be performed.
V. Additional Information:
Previous Similar Occurrences:
A review of License Event Reports from the past 5 years did not identify any similar occurrence.
EIIS System and Component Codes:
IM - Temperature Monitoring System.
Reporting Requirements:
This event is being reported as an Operation or Condition Prohibited by TS, 10CFR50.73(a)(2)(i)(B).