05000237/LER-2002-005
| Dresden Nuclear Power Station Unit 2 | |
| Event date: | 06-04-2002 |
|---|---|
| Report date: | 08-02-2002 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 2372002005R00 - NRC Website | |
A. Plant Conditions Prior to Event:
Unit: 02 � Event Date: 06-04-2002 Reactor Mode: 1 � Mode Name: Run Reactor Coolant System Pressure: 1002 psig
B. Description of Event:
Event Time: 1800 CST Power Level: 95 percent This event is being reported in accordance with 10 CFR 50.73(a)(2)(i)(B), "Any operation or condition which was prohibited by the plant's Technical Specifications.
On June 4, 2002, the Instrument Maintenance Department (IMD) began performance of a monthly calibration surveillance for the pressure switches associated with reactor pressure vessel relief valves. During the performance of the surveillance IMD discovered that the pressure switch setpoint for valve 2-203-3A (as found at 1134.6 psig) exceeded the Technical Specification (TS) Allowable Value (AV) of switch was readjusted to within as left tolerances per station procedure. Following calibration of the pressure switch for valve 2-203-3A, IMD began the calibration for pressure switch associated with valve 2-203-3B and discovered that the pressure switch setpoint exceeded the TS AV of The pressure switch was readjusted to within as left tolerances per station procedure. The remaining three pressure switches were tested in accordance with the station procedure and found to be within the TS required AV.
C. Cause of Event:
During the performance of the pressure switch calibration procedure, test pressure is reduced to zero after "as- found" data is collected and before the pressure switch is calibrated. This current practice of reducing pressure to zero has been determined to promote instrument drift. These pressure switches utilize a 50-1200 psig range Bourdon Tube sensor. The practice of reducing pressure allows the Bourdon Tube sensor to fully relax. Relaxing of the Bourdon Tube sensor creates a shift in the Bourdon Tube sensor elasticity that promotes setpoint drift.
The cause of the event was determined to be procedure instruction deficiency which reduces test pressure to zero after 'as found' data is collected and before the pressure switch is calibrated which promotes instrument setpoint drift. (NRC Cause Code D)
D. Safety Analysis:
The as-found condition of the two (2) pressure switches would have resulted in a slight delay in the opening of their associated reactor pressure vessel relief valves. The as-found pressures for valve 2-203-3A and 2-203-3B were 1.1 and 0.1 psig higher than their associated TS AV, respectively. Therefore, no failure of the valves actually occurred. Both valves would have operated to mitigate reactor pressurization events. Additionally, the reactor pressure vessel safety valves were operable at the time of this occurrence to aid in the mitigation of pressure transients. At no time did this condition compromise the health and safety of the public.
. � NRC FORM 366A � U.S. NUCLEAR REGULATORY APPROVED BY OMB NO. 3150-0104 EXPIRES 07/3112004 collection request: 50 hrs. Reported lessons learned are incorporated into the licensing process and fed back to industry. Forward comments regarding burden estimate to the information and Records Management Branch (t-6 f33), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, and to the Paperwork Reduction Project (3150-0104), Office Of Management 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.
COMMISSION
(LER) (7-2001)
LICENSEE EVENT REPORT
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6 PAGE (3) Dresden Nuclear Power Station Unit 2 05000237 (If more space is required, use additional copies of NRC Form 366A)(17)
E. Corrective Actions:
Pressure switches were immediately adjusted within procedure tolerances.
A review was performed on all Technical Specification related instrument maintenance procedures that test Bourdon Tube sensor type pressure switches and the identified instrument maintenance station procedures were revised to maintain operating pressure at the pressure switch during the performance of the surveillance.
Design Engineering will evaluate setpoints and tolerances for DIS 0250-03.
F. Previous Occurrences:
None
G. Component Failure Data:
N/A