05000331/LER-2010-002
| Document Numbersequential Revmonth Day Year Year Month Day Year 05000Number No. | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor |
| 3312010002R01 - NRC Website | |
I. Description of Event:
On January 4, 2010, at 0324, with the unit operating at 100% power, both Turbine Bypass Valves (TBV1 and TBV2) unexpectedly repositioned from the expected closed position to open causing reactor power to spike to 105%. At 0326 Abnormal Operating Procedure (AOP) 255.2, Power/Reactivity Abnormal Change was entered. In addition, this condition resulted in entry into unplanned LCO 3.7.7 Condition A for both TBVs being inoperable at 0328. At 0329, a fast power reduction was commenced in accordance with Integrated Plant Operating Instruction (IPOI) 4, Shutdown. Power redUctions were secured at 0410 when power was reduced to 68%. At 0448, both TBVs returned to their closed positions. In order to comply with LCO 3.7.7, Condition A, a Minimum Critical Power Ration (MCPR) penalty was applied at 0520 and LCO 3.7.7 was subsequently exited. Subsequently, the TBVs again unexpectedly repositioned to full open at 0545 and closed at 0656. At 0700, both TBVs again unexpectedly repositioned to full open. The TBVs remained full open until they both closed at 1334. On January 5, 2010, at 0022, the TBVs were jumpered closed per Corrective Work Order A101823. The TBVs were declared operable on January 5, 2010 at 1354 when a failed circuit card was replaced.
On January 11, 2010, it was discovered that on January 4, 2010, a condition prohibited by Technical Specifications (TS) existed. Specifically, a TS violation occurred when it was not recognized that TS LCO 3.3.1.1, Reactor Protection System (RPS) and 3.3.4.1, End Of Cycle - Recirculation Pump Trip (EOC-RPT) were not met when the Turbine Bypass Valves (TBVs) were in the open position (TS LCO 3.7.7). The LCO conditions existed for approximately 6.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> — from 0700 until 1334. LCO 3.3.1.1 requires RPS trip capability to be restored within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> and LCO 3.3.4.1 requires an MCPR penalty to be inserted within 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />. If these actions are not completed, then the plant is required to be less than 26% Rated Thermal Power (RTP) within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> thereafter. Because reactor power was not reduced to less than 26% RTP within the 5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> (total) required by LCO 3.3.1.1, a condition prohibited by TS existed for approximately 1.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br />, until the TBVs both closed at 1334. Additionally, because reactor power was not reduced to less than 26% RTP within the 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> (total) required by LCO 3.3.4.1, a condition prohibited by TS existed for approximately 0.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br />, until the TBVs both closed at 1334.
II. Assessment of Safety Consequences:
The TBVs, if open or inoperable at power levels between 26% and 39% power, may cause the Turbine Control Valve (TCV) and Turbine Stop Valve (TSV) Scrams and Recirculation Pump Trip (RPT) trips to be improperly bypassed due to the diversion of steam flow away from the Turbine First Stage Pressure (TFSP) switch which automatically bypasses these trips when reactor power is less than 26%. During the period of time that the condition prohibited by TS existed, reactor power was never less than 39%. Therefore, there was no actual impact on safety. In addition, there were no structures, systems, or components (SSCs) that failed during this event.
This event did constitute an event or condition that could have prevented fulfillment of a safety function and therefore, resulted in a safety system functional failure. This is due to the fact that the unplanned inoperability of all trains of redundant safety systems is subject to the requirements of 10 CFR 50.73(a)(2)(v).
This event did not result in any radiological or nuclear concern which would impact the health and safety of the public.
III. Cause of Event:
An Apparent Cause Evaluation (ACE 2026) was completed for this event. The ACE determined that the Plant staff did not have a full/complete understanding of the relationship between TBVs being open and the direct impact on the TFSP trip/enable setpoint in determining TS compliance/Operability. The contributing factors were as follows:
1. TS Bases has incorrect information and was not well human factored.
2. The Surveillance Test Procedure for TBVs, STP 3.7.7-01, contains misleading information on maintaining TS Operability.
3. Training of Operators was ineffective in understanding this relationship, coupled with the wording of SR 3.3.1.1.16 and 3.3.4.1.5 being stated in % RTP, not TFSP (psig).
IV. Corrective Actions:
Corrective Actions to Address Condition LAR054181 has been initiated to track the identified Bases changes. The focus of this action is on correcting the error in RPS and providing better cross-references between TBVs and RPS/EOC-RPT.
PCR054182 has been initiated to track changes to STP 3.7.7-01. This action will add a Note above the steps that make RPS/EOC-RPT trips inoperable and to add logging information.
OTH045281 has been written to add this event to the classroom exercise guide for the Operations Initial License Training (ILT) program.
0E045134 has been written to share this event with external peers.
RFT054367 has been written to include this event in the License Operator Re-qualification (LOR) training program.
V. Additional Information:
Previous Similar Occurrences:
A review of LERs over the previous 5 years revealed the following similar occurrence:
EIIS System and Component Codes:
TG - Main Turbine Control Fluid System IT - Main Turbine Instrumentation System TA - Main Turbine System Reporting Requirements:
This event is reportable under 10CFR50.73(a)(2)(i)(B), 'Operation or Condition Prohibited by Technical Specification,' and 10CFR50.73(a)(2)(v)(A) and (D), 'Event or Condition That Could Have Prevented Fulfillment of a Safety Function.'