05000446/LER-2011-004
| Comanche Peak Nuclear Power Plant Unit 2 | |
| Event date: | 07-11-2011 |
|---|---|
| Report date: | 09-09-2011 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(vii)(D), Common Cause Inoperability |
| 4462011004R00 - NRC Website | |
I. DESCRIPTION OF THE REPORTABLE EVENT
A. REPORTABLE EVENT CLASSIFICATION:
10CFR50.73(a)(2)(vii)(D) "Any event where a single cause or condition caused two independent trains to become inoperable in a single system designed to mitigate the consequences of an accident".
B. PLANT CONDITION PRIOR TO EVENT:
On July 11, 2011, CPNPP Unit 1 was in Mode 3 while CPNPP Unit 2 was in Mode 1 operating at 100% power.
C. STATUS OF STRUCTURES, SYSTEMS, OR COMPONENTS THAT WERE INOPERABLE AT THE
START OF THE EVENT AND THAT CONTRIBUTED TO THE EVENT
There were no inoperable structures, systems, or components that contributed to the event.
D. NARRATIVE SUMMARY OF THE EVENT, INCLUDING DATES AND APPROXIMATE TIMES:
On July 11, 2011, at 0600 hours0.00694 days <br />0.167 hours <br />9.920635e-4 weeks <br />2.283e-4 months <br />, CPNPP Unit 1 initiated a mid cycle outage to repair secondary system equipment. Tasks were being performed to secure the turbine and secondary systems and cool down and depressurize the Unit 1 Reactor Coolant system to Mode 4. At approximately 0930 hours0.0108 days <br />0.258 hours <br />0.00154 weeks <br />3.53865e-4 months <br /> on July 11, 2011, a Safety Injection (SI) Accumulators", step 5.2.C, to close the 480 volt AC breakers [EllS:(BKR)] providing power to the four Unit 1 Safety Injection (SI) Accumulator Injection Valve motor operators [EllS:(BQ)(ISV)]. The NEO was provided a current revision copy of the Unit 1 procedure, SOP-202A, for in-hand use during the activities. The NEO then traveled to the Operations tool staging area on elevation 832 ft in the Unit 2 Safeguards Building to Train A Emergency Switchgear room on elevation 810 ft. where he located the incorrect (Unit 2) SI Accumulator Injection Valve motor operator circuit breakers and contacted the Unit 1 Reactor Operator (RO) (Utility, Licensed) via the plant page system. The Unit 1 RO then verbally confirmed the procedure identity and step to be performed. Believing he was located in the Unit 1 Safeguards Building, the NEO then repeated back/confirmed the Unit 1 procedure and step identity as correct. When the NEO received the approval to proceed from the Unit 1 RO, he then performed the SOP-202A procedural step on the Unit 2 Emergency Switchgear Train A and B breakers believing that he was performing the activities on Unit 1 equipment. After completing the procedure step, the NEO contacted the Unit 1 RO and the Unit 1 RO then attempted to close the four Unit 1 SI Accumulator Injection Valves. When no indications of valve position change were received, the Unit 1 RO asked the NEO to verify which Unit he was working in and the NEO realized he had performed the steps on the Unit 2 Emergency Switchgear breakers containing similar tag numbers, rather than the correct Unit 1 breakers.
E. THE METHOD OF DISCOVERY OF EACH COMPONENT OR SYSTEM FAILURE, OR PROCEDURAL
PERSONNEL ERROR
Reactor Operator (RO) attempted to close the Unit 1 Safety Injection (SI) Accumulator Injection Valves using the Unit 1 Control Room handswitches.
II. COMPONENT OR SYSTEM FAILURES
A. CAUSE OF EACH COMPONENT OR SYSTEM FAILURE
Not applicable - No component failures were identified during this event.
B. FAILURE MODE, MECHANISM, AND EFFECTS OF EACH FAILED COMPONENT
Not applicable - No component failures were identified during this event.
C. SYSTEMS OR SECONDARY FUNCTIONS THAT WERE AFFECTED BY FAILURE OF COMPONENTS
WITH MULTIPLE FUNCTIONS
Not applicable - No component failures were identified during this event.
D. FAILED COMPONENT INFORMATION
Not applicable - No component failures were identified during this event.
III. ANALYSIS OF THE EVENT
A. SAFETY SYSTEM RESPONSES THAT OCCURRED
Not applicable - No safety system responses occurred as a result of this event.
B. DURATION OF SAFETY SYSTEM TRAIN INOPERABILITY
The four (4) Unit 2 Safety Injection accumulators were inoperable from 1035 CDT to 1115 CDT on July 11, 2011.
C. SAFETY CONSEQUENCES AND IMPLICATIONS OF THE EVENT
Power is required to be removed from the Safety Injection Accumulator Isolation Valve motor operators when RCS pressure is greater than 1000 psig per Technical Specification surveillance requirement (SR) 3.5.1.5. The valves were always fully open and could not be closed due to the key-lock switch in the Control Room being in the OFF position and the P-11 interlock which automatically opens the valves whenever Pressurizer pressure is greater than 1960 psig. If an event had occurred, the Accumulators would have been available to perform their safety function. Consequently, this event resulted in no actual safety consequences and there were no safety system functional failures associated with this event.
IV. CAUSE OF THE EVENT
The cause of this event was the failure of the worker to utilize the expected error prevention tools based upon the incorrect assumption that the Operator was in the correct Unit.
V. CORRECTIVE ACTIONS
The CPNPP Unit 2 Unit Supervisor declared all four (4) Unit 2 Safety Injection accumulators inoperable and entered TS 3.5.1, Condition D and LCO 3.0.3 at 1035 CDT on July 11, 2011. The Unit 2 Safety Injection (SI) Accumulator Isolation Valve motor operator breakers were re-opened to restore compliance with TS 3.5.1. LCO 3.0.3 was exited at 1115 on July 11, 2011.
The Unit 1 Control Room Operators reduced the RCS cool down and depressurization rate and directed a different, qualified NEO to close the Safety Injection (SI) Accumulator Isolation Valve motor operator breakers for Unit 1 prior to resuming the Unit 1 RCS cool down and depressurization.
The NEO originally assigned to perform the activity was removed from assigned plant operation activities. A performance enhancement plan has been developed and is being conducted for the operator in question to reinforce station expectations regarding usage of error reduction tools.
On July 12, 2011, the Director, Operations, issued an "Operations Human Performance Event Communication" to the Station Managers and Supervisors for communication and awareness of the event among all departments.
VI. PREVIOUS SIMILAR EVENTS
There have been no previous similar reportable events at CPNPP in the last three years.