05000249/LER-2004-005
| Dresden Nuclear Power Station | |
| Event date: | 09-29-2004 |
|---|---|
| Report date: | 11-29-2004 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability |
| 2492004005R00 - NRC Website | |
Dresden Nuclear Power Station Unit 3 is a General Electric Company Boiling Water Reactor with a licensed maximum power level of 2957 megawatts thermal. The Energy Industry Identification System codes used in the text are identified as [XX].
A. Plant Conditions Prior to Event:
Unit: 03 Event Date: 9-29-2004 Reactor Mode: 1 Mode Name: Power Operation Power Level: 100 percent Reactor Coolant System Pressure: 1000 psig
B. Description of Event:
On September 29, 2004, at 1235 hours0.0143 days <br />0.343 hours <br />0.00204 weeks <br />4.699175e-4 months <br /> (CDT), with Unit 3 at approximately 100 percent power in Mode 1, it was discovered that 3 of the 4 Unit 3 Isolation Condenser (IC) [BL] Time Delay Relays [RLY], 3-0595-117A, 3-0595-117B, and 3-0595-117C, exceeded their Allowed Value specified in Technical Specification (TS) 3.3.5.2, "Isolation Condenser (IC) System Instrumentation." TS Surveillance Requirement 3.3.5.2.3 requires that the Allowable Value of the time delay portion of the instrument channel be less than or equal to 15 seconds. Time Delay Relay 3-0595-117A was measured to be 15.2 seconds, 3-0595-117B was 15.8 seconds, and 3-0595-117C was 15.1 seconds. The event was discovered while performing Surveillance Procedure DIS 1300-08, "Sustained High Reactor Pressure Time Delay Relay Calibration." The IC Time Delay Relays were previously calibrated on June 16, 2002.
The Unit 3 IC Time Delay Relays were recalibrated to less than or equal to 15 seconds on September 29, 2004. On October 12, 2004, the Unit 2 IC Time Delay Relays were tested and all relays had an as-found measured time delay of less than or equal to 15 seconds.
This event is being reported in accordance with:
■ 10 CFR 50.73(a)(2)(vii), "), "Any event where a single cause or condition caused at least one independent train or channel to become inoperable in multiple systems or two independent trains or channels to become inoperable in a single system." This event identified that two independent channels of the time delay portion of the Unit 3 IC Initiation Logic were inoperable, and ■ 10 CFR 50.73(a)(2)(i)(B), "Operation or condition prohibited by Technical Specifications." TS 3.3.5.2 requires that the IC System be declared inoperable when IC instrument channels are inoperable for greater than 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. TS 3.5.3, "IC System," requires that with an inoperable IC System not restored to operable within 14 days, the plant 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 /> and reactor steam dome pressure be less than or equal to 150 pounds per square inch gage within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />. The evaluation of this event concluded that historically the IC instrument channels were inoperable for greater than 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> and the required actions of TS 3.5.3 were not accomplished in the TS allowed completion time.
C. Cause of Event:
The root cause of the event was due to an ineffective extent of condition review for a corrective action associated with a 1996 event in which stopwatches were determined to not be sensitive enough for calibration checks on components with limited margin.
A 1996 investigation of a Unit 3 Anticipated Transient Without Scram (ATWS) Time Delay out of tolerance event was described in Dresden Unit 3 Licensee Event Report (LER)96-012, "Out of Tolerance Anticipated Transient Without SCRAM Time Delay Relay due to Inadequate "As Found" Calibration Check Method." The LER identified that a stopwatch was not sensitive enough for calibration checks on components with limited margin. In 1996, one of the corrective actions was to review other Dresden procedures, which check time delay relays and revise them as required to ensure that the testing methodology is appropriate for the installed configuration. Review of the closure of this corrective action showed that 8 procedures associated with Emergency Core Cooling Systems and Reactor Protective System were revised. However, the IC Time Delay Relays were not identified as affected components and the relay calibration procedure was not revised. The 2004 investigation was unable to determine why the IC procedure was not revised as a result of the 1996 ATWS investigation.
A 2002 investigation of Unit 2 IC Time Delay Relay surveillance failures was described in Dresden Unit 2 LER 2002-001, "Unit 2 Isolation Condenser Time Delay Relay Surveillance Failures due to Setpoint Specified with No Margin." The LER identified that the root cause was determined to be an inadequate setpoint calculation that did not provide for setpoint drift. Additionally, the LER identified that the IC Time Delay Relay procedure was to be revised to specify the use of a strip chart recorder instead of a stopwatch during relay calibration. The IC procedure was revised on June 26, 2002.
However, the previous calibration of the Unit 3 IC Time Delay Relay was performed on June 16, 2002 and a stopwatch was used during the calibration.
D. Safety Analysis:
The safety significance of the event is minimal. An engineering evaluation concluded that the as- found condition of the IC Time Delay Relays would have resulted in IC initiation sooner than assumed in the Loss of Feedwater Transient. Additionally, the TS Bases for the IC System states that although the IC is an Engineered Safety Features System, no credit in taken in the Dresden accident analyses for IC System operation. Therefore, the consequences of this event had minimal impact on the health and safety of the public and reactor safety.
E. Corrective Actions:
The IC Time Delay Relay procedure DIS-1300-08 was revised to require the use of a strip chart recorder with pre-calibration and post-calibration checks, for calibration of the IC Time Delay Relays.
The Unit 2 and Unit 3 IC Time Delay Relays were recalibrated with the revised DIS-300-08 procedure.
F. Previous Occurrences:
A review of Dresden Nuclear Power Station LERs over the previous eight years identified the following similar occurrence associated with failed time delay relays.
■ Dresden Unit 3 LER 96-012, "Out of Tolerance Anticipated Transient Without SCRAM Time Delay Relay due to Inadequate "As Found" Calibration Check Method." The LER identified that a stopwatch was not sensitive enough for calibration checks. One of the corrective actions was to review other Dresden procedures, which check time delay relays and revise them as required to ensure that the testing methodology is appropriate for the installed configuration. The IC Time Delay Relay was not identified as an affected component and the relay calibration procedure was not revised. The 2004 investigation was unable to determine why the IC procedure was not revised as a result of the 1996 ATWS investigation.
■ Dresden Unit 2 LER 2002-001, "Unit 2 Isolation Condenser Time Delay Relay Surveillance Failures due to Setpoint Specified with No Margin." The LER identified that the root cause was determined to be an inadequate setpoint calculation that did not provide for setpoint drift.
Additionally, the LER identified that the IC Time Delay Relay procedure was to be revised to specify the use of a strip chart recorder instead of a stopwatch during relay calibration. The IC procedure was revised on June 26, 2002. However, the previous calibration of the Unit 3 IC Time Delay Relay was performed on June 16, 2002 and a stopwatch was used during the calibration.
G. � Component Failure Data:
N.A.