05000237/LER-2001-005
| Dresden Nuclear Power Station Unit 2 | |
| Event date: | |
|---|---|
| Report date: | |
| 2372001005R00 - NRC Website | |
LICENSEE EVENT REPORT (LER) f33), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, And Budget, Washington, DC 20503. If 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.
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3) Dresden Nuclear Power Station Unit 2 05000237 NUMBER NUMBER (If more space is required, use additional copies of NRC Form 366A)(17)
A. Plant Conditions Prior to Event:
Unit: 02 � Event Date: 11-07-2001 Reactor Mode: 2 � Mode Name: Startup Reactor Coolant System Pressure: 930 psig
B. Description of Event:
Event Time: 2003 Power Level: 8 percent This event is being reported in accordance with 10 CFR 50.73 (a)(2)(iv)(A), which requires the reporting of any event or condition, which resulted in manual or automatic actuation of the Reactor Protection System (RPS).
On November 07, 2001 at 2003 hours0.0232 days <br />0.556 hours <br />0.00331 weeks <br />7.621415e-4 months <br />, Dresden Nuclear Power Station (DNPS) Unit 2 automatically scrammed from 8 percent power in Mode 2 following a scheduled refueling outage. Initial investigation revealed that high- pressure turbine first stage pressure which was procedurally required to be maintained between 60 — 100 psig, had risen during shell warming to defeat the stop valve closure SCRAM bypass. A reactor scram was initiated when this high-pressure was sensed along with the turbine stop valves being closed.
During the fall outage for Unit 2 (D2R17) a new high-pressure turbine and cross around relief valves (CAR) were installed. Extensive work on all other turbine valves was also performed. In preparation for Extended Power Uprate (EPU), the reactor SCRAM bypass setpoint was also lowered from 292 psig to 209 psig. This setpoint is derived from the turbine first stage pressure. In addition, the CAR valve minimum setpoints were raised from 261 psig to 297 psig. In previous startups the CAR valves could lift prior to achieving the pressure setpoint when the scram bypass signal would be disabled. Also during previous startups, the turbine would "roll" off of the turning gear when shell pressure exceeded 120 psig and turbine first stage pressure would not exceed 150 psig. With the new high-pressure turbine, the Combined Intercept Valve (CIV) work and installation of the new CAR valves, the system was more pressure tight than previous startups. This allowed turbine first stage pressure to increase to a higher value than previously associated with the startup process.
At the time of the event, shell and chest warming had been in progress. Turbine startup was delayed for 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> due to increased sulfates in the reactor water, which prohibited entry into Mode 1. Additionally, several activities were being conducted in the control room, which provided distractions to the startup evolution. Finally, the NSO that began the shell warming activities was sent to Just In Time (JIT) training in preparation for the turbine roll.
Past experience had shown that when the turbine first stage pressure was high, the turbine rolled off of the gear and adjustment would be required to the turbine stop valve to reduce pressure. During this event when the turbine was placed back on gear, the operator had a false sense of security during this evolution that the first stage pressure had been controlled. The Unit Supervisor and Shift Manager were aware of the turbine roiling off of gear.
This was identified as a possibility in the turbine startup procedure. When this occurred, the turbine was placed back on gear and turbine preparation continued. When the turbine first stage pressure exceeded 209 psig, the reactor SCRAM bypass was disabled. Due to the turbine stop valves being closed, the Reactor Protection System (RPS) [JC] logic to initiate a full reactor SCRAM was enabled.
LICENSEE EVENT REPORT (LER) f33), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, And Budget, Washington, DC 20503. If 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.
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3) Dresden Nuclear Power Station Unit 2 05000237 NUMBER NUMBER (If more space is required, use additional copies of NRC Form 366A)(17)
C. Cause of Event:
The root cause of the event was determined to be inadequate human performance in that turbine first stage pressure setpoint was inadequately monitored (as required by procedure) due to it not being considered a critical parameter required for turbine startup. (NRC Cause Code A)
D. Safety Analysis:
All automatic protection responses, including reactor trip and its associated actuations were verified to have functioned properly as a result of the reactor trip signal. Based on the above, it is concluded that the event did not adversely impact the health and safety of the public. The risk for this event is considered minimal and there was no increase in Core Damage Frequency (CDF).
E. Corrective Actions:
Training on this event was provided to Operations regarding the effect on Unit 2 with respect to turbine first stage SCRAM setpoint changes due to implementation of Extended Power Uprate and the relationship between shell warming and its impact on RPS logic.
Enforcement of expectations with regard to adherence to established operations standards was performed by the Shift Operations Supervisor (SOS) to all Operations crews.
Panel monitoring expectations were established by the SOS and incorporated into Operations standing orders.
Revised the operations procedure for Main Turbine Startup, to include a requirement to place an operator selected alarm that forces a control room annunciator alarm when 100 psig for first stage pressure is exceeded.
The Unit Supervisor and the Nuclear Shift Operator were removed from duty and worked to develop the modified Operations Start-Up plan based on the event. Both were counseled with respect to this event and returned to duty.
F. Previous Occurrences:
A review was conducted via a search of previous events of this type. No events of this type were found for DNPS.
G. Component Failure Data:
N/A