05000446/LER-2013-002
| Comanche Peak Nuclear Power Plant (Cpnpp) Unit 2 | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 4462013002R00 - NRC Website | |
I. DESCRIPTION OF THE REPORTABLE EVENT
A. REPORTABLE EVENT CLASSIFICATION:
50.73(a)(2)(iv)(A) "Any event or condition that resulted in manual or automatic actuation of any of the systems listed in paragraph (a)(2)(iv)(B).
B. PLANT CONDITION PRIOR TO EVENT:
On November 1, 2013, Comanche Peak Unit 2 was in Mode 1, Power Operation, operating at approximately 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 were inoperable at the start of the event that contributed to the event.
D. NARRATIVE SUMMARY OF THE EVENT, INCLUDING DATES AND APPROXIMATE
TIMES:
Procedure OPT-406B-1 performs the surveillance test of the Unit 2 Train A K620 slave relay. The test utilizes a blocking circuit to verify the operability of the slave relay which trips the main turbine and both main feedwater pump turbines, on a HI-HI steam generator level or safety injection (SI). No actuation should occur.
The procedure step 17 turns switch 2-TS-1/K620 to the PUSH TO TEST position. The PUSH TO TEST position establishes the block of the main turbine and feedwater trip signal from auxiliary relay 2-10CA/0620A. Step 18 verifies the block, then step 19 actuates the relay by depressing the switch.
On November 1, 2013 at 2146 CST, the Unit 2 Reactor Operator (utility, licensed) at the CP2-EIPRCV-13 cabinet in the control room was turning switch 2-TS-1/K620 to the PUSH TO TEST position in accordance with procedure OPT-406B-1 step 17 when the unanticipated trip of the main turbine and feedwater pumps occurred followed by automatic actuation of a reactor trip. The control room operators immediately entered procedure EOP-0.0B, "Reactor Trip or Safety Injection" in response to the reactor trip.
Operations issued a shift order on 11/05/2013 to not perform slave relay testing involving blocking circuits for the main turbine and main feedwater pumps until further notice.
These include all tests utilizing test switches in the main turbine and feedwater pump test cabinets.
E. THE METHOD OF DISCOVERY OF EACH COMPONENT OR SYSTEM FAILURE, OR
PROCEDURAL PERSONNEL ERROR
Operators (utility, licensed) in the Unit 2 Control Room received a Unit 2 steam generator Hi-Hi level trip.
II. COMPONENT OR SYSTEM FAILURES
A. CAUSE OF EACH COMPONENT OR SYSTEM FAILURE
Not applicable — There were no component or system failures.
B. FAILURE MODE, MECHANISM, AND EFFECTS OF EACH FAILED COMPONENT
Not applicable - There were no component or system failures.
C. SYSTEMS OR SECONDARY FUNCTIONS THAT WERE AFFECTED BY FAILURE OF
COMPONENTS WITH MULTIPLE FUNCTIONS
Not applicable — There were no component or system failures.
D. FAILED COMPONENT INFORMATION
Not applicable - There were no component or system failures.
III. ANALYSIS OF THE EVENT
A. SAFETY SYSTEM RESPONSES THAT OCCURRED
Both motor driven auxiliary feedwater pumps and the turbine driven auxiliary feedwater pump started as expected as a result of the reactor trip.
B. DURATION OF SAFETY SYSTEM TRAIN INOPERABILITY
Not applicable - there was no safety system train inoperability that resulted from this event.
C. SAFETY CONSEQUENCES AND IMPLICATIONS OF THE EVENT
This event is bounded by the CPNPP Final Safety Analysis Report (FSAR) accident analysis which assumes conservative initial conditions which bound the plant operating range and other assumptions which could reduce the capability of safety systems to mitigate the consequences of the transient.
This event is bounded by the analysis of the turbine trip presented in Section 15.2.3 of the CPNPP FSAR. The analysis uses a conservative assumption to demonstrate the capability of pressure relieving devices and to demonstrate core protection margins. The event of November 1, 2013, occurred at 100% reactor power, and all systems and components functioned as designed.
Based on the above, it is concluded that the health and safety of the public were unaffected by this condition and this event has been evaluated to not meet the definition of a safety system functional failure per 10CFR50.73(a)(2)(v).
IV. CAUSE OF THE EVENT
The direct cause of the event was an invalid input from switch 2-TS-1/K620 during the rotation to the PUSH TO TEST position that resulted in the unanticipated actuation of auxiliary relay 2- KXA/0620 before blocking the output with relay 2-KT/0080-1.
The cause is that the original design for the 2-KXA/0620A test circuit in CP2-EIPRCV-13 did not include an electrical interlock to address the possibility of the 2-TS-1/K620 L21-L22 contact closing prior to establishing the block of end device actuation.
V. CORRECTIVE ACTIONS
The interim corrective action is to not perform the test in Mode 1. The long term corrective action is to add a test signal electrical interlock with the blocking relay to prevent slave relay actuation until the block is established for test circuits in Units 1 and 2.
VI. PREVIOUS SIMILAR EVENTS
There have been no previous similar reportable events at CPNPP in the last three years.