05000336/LER-2006-004

LER-2006-004, Failure to Enter the Technical Specification Action Statement for Inoperable Reactor Protection System Trips

Docket Number
Event date:	04-13-2006
Report date:	06-09-2006
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
3362006004R00 - NRC Website

1. Background For MPS Unit 2, the Reactor Protection System (RPS) [JC] consists of 4 separate channels each containing a bistable trip unit for the following parameters:

• Reactor Power Level — High

• Steam Generator Water Level — Low

• Reactor Coolant Flow — Low

• Local Power Density — High

• Pressurizer Pressure — High

• Thermal Margin/Low Pressure (TM/LP)

• Containment Pressure — High

• Loss of Turbine — Hydraulic Fluid Pressure — Low

• Steam Generator Pressure — Low The TM/LP, and the Reactor Coolant System (RCS) [AB] Low Flow reactor trips, and the AT input to the Reactor Power Level — High reactor trip may be bypassed if reactor power, as determined by the Wide Range Nuclear Instrumentation (WRNI), is less than 5% rated thermal power. Above this power level the ability to bypass these trips/inputs is automatically removed.

While the WRNIs are not specifically required by TS to be operable in Modes 1, and 2, they provide input to the automatic bypass defeat function for the TM/LP, RCS Low Flow, and Reactor Power Level — High RPS trips.

These trips are required in Modes 1 and 2. TS LCO 3.3.1.1 requires that, "as a minimum, the reactor protective (RPS) instrumentation channels and bypasses of table 3.3-1 shall be OPERABLE." If a WRNI channel is removed from service, the automatic removal of the TM/LP, RCS Low Flow, and Reactor Power Level — High bypass is also lost for that channel.

2. Event Description Technical Specification Action Statement (TSAS) 3.3.1.1 Action 2 requires that with the number of operable channels one less than the total number of channels, "operation may continue" provided the inoperable channel is placed in either the bypassed or tripped condition within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />. Failure to place the channel in bypass or trip would require entry into TSAS 3.0.3 to facilitate a shutdown of the unit.

A review of the maintenance history for the last three years indicated that on several occasions (10) the WRNI channels were calibrated in Mode 1. During this maintenance activity the TM/LP, RCS Low Flow, and Reactor Power Level — High reactor trips were not placed in the bypassed or tripped condition per TSAS 3.3.1.1 Action 2, and TSAS 3.0.3 was not entered. In each of these instances the duration of the maintenance activity exceeded the time allowed by TSAS for completion of the required actions. On this basis the condition is reportable pursuant to 10 CFR 50.73(a)(2)(i)(B), as operation in a condition prohibited by the Technical Specifications.

3. Cause The cause was determined to be a weakness in licensed operator knowledge of the relationship between the WRNIs and the RPS Automatic Bypass Defeat function in that although the WRNIs are not specifically required by TS to be operable in Modes 1, and 2, they provide input to the automatic bypass defeat function for the TM/LP, RCS Low Flow, and Reactor Power Level — High RPS trips. These trips are required in Modes 1 and 2.

4. Assessment of Safety Consequences In order to bypass the TM/LP, RCS Low Flow, and Reactor Power Level - High reactor trips, the reactor must be calibration of the WRNIs the Zero Mode Bypass Switch is in the normal (off) position, therefore, the TM/LP, RCS Low Flow, and Reactor Power Level - High reactor trips were always available. Accordingly, there are no safety consequences associated with this event.

5. Corrective Action The actions to prevent recurrence include training the Operators on this incident, revision of appropriate station procedures to address this incident, and evaluating the need for a TS change.

Additionally a Night Order has been issued instructing the operators to declare the TM/LP, RCS Low Flow, and Reactor Power Level - High reactor trips inoperable for the affected channel and enter TSAS 3.3.1.1. Action 2, when the associated WRNIs are inoperable.

Additional corrective actions are being taken in accordance with the station's corrective action program.

6. Previous Occurrences No previous similar events/conditions were identified.

Energy Industry Identification System (ENS) codes are identified in the text as [XX].