05000266/LER-2007-004

LER-2007-004,

Docket Number
Event date:	06-05-2007
Report date:	08-02-2007
Reporting criterion:	10 CFR 50.73(a)(2)(iv)(A), System Actuation
2662007004R00 - NRC Website

Event Description

On June 5, 2007, the Unit 1 reactor was manually tripped due to the inability to control main feedwater flow to the 'B' steam generator. The condition occurred because a nut for the bolt which secures the valve position feedback arm to the positioner output shaft came off allowing the two linkages to separate. The lack of position feedback caused control of the valve to be lost and steam generator level to cycle between 70% and 78%. A decision was made to manually trip the reactor. AOP 2B, Feedwater System Malfunction, was being utilized prior to the trip.

Unit 1 was in Mode 1 at 100% power prior to the reactor trip and was stabilized in Mode 3 following the trip.

Motor-driven auxiliary feedwater pump P-38B and turbine-driven auxiliary feedwater pump 1P-29 appropriately started in response to plant conditions and were secured when steam generator levels were controlled using the feedwater regulating valve bypass valves.

Event Analysis

The event was a manual reactor trip in response to the inability to control level in one steam generator.

Appropriate procedures were followed. Equipment and personnel functioned appropriately except for three minor unexpected conditions.

An unexpected electrical lockout of 345 kV switchyard Bus Section 2 occurred. One moisture separator reheater drain valve failed to automatically shut and was manually shut. One turbine bearing oil lift pump failed to automatically start and was manually started.

Bus Section 2 connects to the Unit 1 generator output. The lockout was in response to a delay in opening the A-phase pole. The delay was caused by improperly adjusted auxiliary switches in the breaker control cabinet. The improper adjustment was made during the previous refueling outage during a timing test performed by WE Energies personnel. The lockout of the bus section did not impact the response to the reactor trip. The preventive maintenance callup forms have been changed to include notification of System Engineers if auxiliary switches require adjustment.

One moisture separator reheater drain valve, 1FD-02603, failed to automatically shut and was manually, shut. The function of the drain valve is to prevent steam within the reheat system from reaching the turbine and causing an overspeed condition. The automatic failure did not impact the response to the reactor trip because a redundant valve, 1FD-02604, located in series with the affected valve, successfully shut, thus providing the same function.

One turbine bearing oil lift pump, 1P-129A for the Number 3 bearing, did not automatically start following the reactor trip. The pump was manually started. The cause of the start failure is being investigated via work order W0333160.

Steam generator 'B' level control was lost when the feedback arm from the main feedwater regulating valve became separated from the valve positioner. The separation was due to a nut coming off a connecting bolt.

A root cause evaluation is being performed on the loss of the nut.

FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6 PAGE (3)

Cause

A manual reactor trip was initiated due to the loss of a nut with subsequent inability to control steam generator level. The cause for the loss of the nut has been determined to be a procedure inadequacy.

Vendor technical bulletin information on the use of the specific type of locknut on positioner linkages was not completely incorporated into plant maintenance procedures.

Corrective Action The corrective action, which will be tracked via the site's corrective action program, will be to revise the routine maintenance procedure to address linkage fasteners. Corrective Action (CA) 01095358-09 has been issued.

Safety Significance

The plant response during and following the transient, was as expected with three minor noted exceptions which did not impact any safety-related functions nor impair the ability to maintain the plant in a safe, controllable condition. Although the event was a manual actuation of the reactor protection system, plant equipment performance allowed a stable configuration to be maintained. Thus, the safety significance of the event was low and there was no impact on the health and safety of the public, and no impact on employee health and safety.

During this event and the subsequent recovery actions there was no loss of a safety-related system, structure or component. Therefore, the event did not involve a Safety System Functional Failure. The positioner components associated with the main feedwater regulating valves perform a function of normal steam generator water level control only. The safety function for the main feedwater regulating valves is to close on a main steam line break (MSLB). Solenoid valves, which are independent of the position controller, perform the safety function and were not affected by the loss of the connecting nut.

Component and System Description The system affected was Feedwater/Condensate. The particular component was the main feedwater regulating valve; specifically the valve position control equipment. The positioner is a Bailey AP-4 equipped with a position feedback arm connected to a Copes-Vulcan Model 24 valve. The valve is a flow controlling, normally open valve in the main feedwater supply header for the Unit 1 'B' steam generator.

Previous Similar Events

A review of LERs submitted in the past three years, associated with requirement 10 CFR 50.73(a)(2)(iv)(A) for manual or automatic actuation of the reactor protection system, reactor trip, with a cause of procedural inadequacies, was conducted. No similar events were identified.

FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6 PAGE (3) Point Beach Nuclear Plant 05000266 YEAR Failed Components Identified None