05000250/LER-2014-003
| Turkey Point Unit 3 | |
| Event date: | 4-23-2014 |
|---|---|
| Report date: | 6-18-2014 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| Initial Reporting | |
| ENS 50054 | 10 CFR 50.72(b)(3)(iv)(A), System Actuation |
| 2502014003R00 - NRC Website | |
Reported lessons learned are incorporated into the licensing proceSs and fed back to industry.
Send comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch(T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by intemet e-mail to Infocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. II a means used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
2. DOCKET
6. LER NUMER
DESCRIPTION OF THE EVENT
On April 23, 2014 at approximately 1302 hours0.0151 days <br />0.362 hours <br />0.00215 weeks <br />4.95411e-4 months <br />, Unit 3 entered Technical Specification (TS) 3.1.3.3 Action as a result of the Shutdown Bank B Group 1 Step Counter [AA, CTR] failing to increment. The reactor was subcritical in Mode 3 progressing to reactor startup. The reactor operator opened the reactor trip breakers in accordance with the Action of TS 3.1.3.3, which requires that the reactor trip breakers be opened if the group step counter demand position indicator (group 1 and group 2) are not within ± 2 steps of each other. All rods fully inserted. The unit remained in Mode 3.
This was a manual actuation of the Reactor Protection System. Therefore, an 8-hour report (EN# 50054) was made in accordance with 10 CFR 50.72(b)(3)(iv) to the NRC Operations Center. This report is in accordance with 10 CFR 50.73(a)(2)(iv)(A).
CAUSE OF THE EVENT
The direct cause of the event was the failure of the group step counter demand position indicator to increment because the supervisory data logging card A 114 was not fully seated in the circuit card rack.
The root cause is attributed to lack of sufficient instruction in a functional test procedure to verify proper card seating. Card A114 gave a false indication of being fully seated by allowing the urgent failure alarm to clear although complete contact was not established.
ANALYSIS OF THE EVENT
During operation of the Rod Control System (RCS), the Logic Cabinet generates and sends pulses to the Power Cabinets. When the Power Cabinet receives this pulse it initiates a Rod Step. When the Rod Step cycle is complete a reply pulse is sent back to the Logic Cabinet. Once this reply pulse is received at the Logic Cabinet, the Logic Cabinet then triggers a relay which in turn sends out a 100 Vdc pulse to the associated Group (demand) Step Counter on the Control Room Operator's Console. When this pulse is received at the Group (demand) Step Counter the step counter increments in the required direction (+1 if rods out and -1 if rods in). These Group (demand) Step Counters rely on continuity with the RCS. At time of discovery, the A114 printed circuit card was found not fully seated and confirmed as protruding beyond the edge of the card cage assembly by approximately 'A —'A inch. The A114 card was tight, however additional force was required to ensure the card was fully seated.
On April 23, 2014, early in the dayshift, RCS testing was performed in accordance with 0-PMI-028.05, Rod Control System Preventative Maintenance and Power Cabinet Functional Test. In accordance with this procedure, card A114 was withdrawn to verify proper operation of the Urgent Failure Alarm and then re- seated in the card cage. The Urgent Failure Alarm cleared.
Later, while performing cold rod stepping, Operations personnel observed that while the Shutdown Bank B (SBB) rods were withdrawn, the group 2 step counter indicated 7 steps withdrawn, but the group 1 step Reported lessons learned are incorporated into the licensing process and fed back to industry.
Send comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by intemet e-mail to Infocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-1 0202, (3150-0104), Office of Management and Budget, Washington, DC 20503. If a means used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
2. DOCKET
6. LER NUMER
counter remained at 0 steps. The console and the Digital Control System rod position indication both indicated that both the group 1 and group 2 SBB were withdrawn to approximately 7 steps. Operations personnel concluded that the shutdown bank group step counters were not indicating properly and the decision was made to open the Unit 3 reactor trip breakers.
Reportability The event (a manual actuation of the Reactor Protection System) is reportable in accordance with 10 CFR 50.73(a)(2)(iv)(A) because the reactor trip breakers were required to be opened in response to a plant condition.
ANALYSIS OF SAFETY SIGNIFICANCE
At the time of the event, the reactor was in Mode 3 (sub-critical) and the plant remained in Mode 3. The reactor trip breakers were opened and all systems functioned as required. Significant subcriticality margin was available based on the balance of the control rods being fully inserted and the boron concentration being greater than the predicted dilution value for criticality. There was no impact on safety.
CORRECTIVE ACTIONS
Corrective action is in accordance with condition report AR1960842 and includes:
- Revise plant procedure O-PMI-028.05, Rod Control System Preventive Maintenance and Power Cabinet Functional Test, to require a visual inspection and independent verification to verify the engagement of the printed circuit boards (PCB) by ensuring the front edge of the PCBs are flush with the card cage assembly. An additional supervisor visual inspection step will also be added to the procedure.
ADDITIONAL INFORMATION
component function identifier (if appropriate)]. Condition Report 1960842 was initiated due to this event.
FAILED COMPONENTS IDENTIFIED: None.
PREVIOUS SIMILAR EVENTS: None in the last five years.