05000305/LER-2005-003
| Docket Number | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 3052005003R01 - NRC Website | |
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6 PAGE (3)
Event Description:
On February 20, 2005, while the Kewaunee Nuclear Power Plant (KNPP) was in the Intermediate Shutdown mode, an inadvertent Reactor Protection System (RPS) [JC] reactor trip signal was initiated. The RPS signal was initiated when the Lo-Lo Level setpoint (17%) was reached in the "B" Steam Generator (SG) [SG]. The low level condition occurred while cool-down operations were in progress with SG levels being maintained outside of the normal operating procedure control band.
On February 19, 2005, a plant shutdown was initiated due to the plant's Auxiliary Feedwater (AFW) system [BA] being declared inoperable due to a previously reported system protection design deficiency. The plant shutdown was completed at 0509 hours0.00589 days <br />0.141 hours <br />8.416005e-4 weeks <br />1.936745e-4 months <br /> on February 20, 2005 Subsequent to performing required Hot Shutdown mode surveillance tests and completing plant system preparations for establishing Cold Shutdown conditions, a plant cool-down was initiated at 1111 hours0.0129 days <br />0.309 hours <br />0.00184 weeks <br />4.227355e-4 months <br /> on February 20, 2005. Plant cool-down is accomplished by steaming the SGs and maintaining secondary water inventory with the AFW system. Prior to the level trip, until just shortly before the actual signal was generated, only one AFW Pump [P] was being used to maintain SG level.
Prior to and at the onset of the cool-down evolution, Control Room [NA] operators were experiencing difficulties maintaining SG levels within the procedure-required operating band Of 30% to 50%. Attempting to maintain SG inventory by use of only one AFW pump complicates maintaining level control. When only one AFW pump is used to maintain SG inventory, the operator has little control over how much flow can be directed to either of the plant's SGs when feeding both at one time. Consequently, if care is not taken to start a second pump soon enough, level control can be lost. In this event, corrective actions to start a second pump to replenish the depleting "B" SG inventory were not accomplished before the Lo-Lo level setpoint was reached.
During cool-down operations, using two motor [MO] driven AFW pumps provides better control of AFW feed flow to each SG. Each of the pumps has an air operated discharge flow control valve [FCV] whereby the Control Room operator can control the output flow of the associated AFW pump. KNPP's system design is such that the discharge piping of the motor driven AFW pumps can be cross-connected to allow one pump operation to feed both SGs. However, the cross-connect piping connection is downstream of the air operated flow control valves for the pumps. The cross-connect line between the two trains of piping to the SGs is isolable by closing either one or both of two motor operated valves from the Control Room.
In addition to the less than optimal AFW system alignment, other activities that were in process either aggravated the level control difficulties or distracted the on-shift crew. They include:
- Increasing secondary side SG blowdown flow to 50 gpm without notifying the Control Room operator.
- Allowing a SG level of 22%, which is lower than the normal control band limit of 30-50%.
- Attempting to recover from a pre-cool-down evolution that resulted in having to operate one of the SGs in an unusual condition.
- The Control Room Supervisor and Shift Manager were overly interactive with plant activities resulting in distraction from their primary oversight activities.
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6 PAGE (3)
Event Analysis:
This event is being reported under 10CFR 50.73(a)(2)(iv)(A), an event that resulted in automatic actuation of the RPS. The RPS was actuated by the inadvertent initiation of a reactor trip signal when the Lo-Lo Level Setpoint was reached in the "B" SG. The plant had already been placed in a shutdown condition. Therefore, no actual reactor trip occurred.
There is no safety significance to this event. The reactor protection signal was not required to provide any plant or public health and safety need.
Cause:
A root cause evaluation of this event was conducted and determined that this event was attributed to failure to adhere to procedure requirements and inadequate Supervisory/Management oversight.
The operations crew exhibited a misapplication of procedure steps with the knowledge, endorsement, and direction of shift management. Additionally, the Shift Manager and Control Room Supervisor did not maintain appropriate crew oversight during a non-routine transient condition.
Corrective Actions:
1. Individual performance issues associated with this event have been addressed.
2. Procedure use and adherence expectations will be enhanced.
3. Operations crews will be trained and assessed, regarding knowledge of existing and enhanced procedure use and adherence expectations.
4. A simulator exercise will be conducted for each operating crew that reinforces the appropriate behavior required to conduct a plant cool down. The scenario for the exercise will include the obstacles that were encountered during this event.
SIMILAR EVENTS
None.