05000353/LER-2006-001

LER-2006-001, HPCI Ramp Generator Signal Converter Failure

Docket Number
Event date:	10-13-2006
Report date:	12-13-2006
Reporting criterion:	10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident 10 CFR 50.73(a)(2)(v), Loss of Safety Function
Initial Reporting
ENS 42907	10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident
3532006001R00 - NRC Website

Unit Conditions Prior to the Event Unit 2 was in Operational Condition (OPCON) 1 (Power Operation) at approximately 100% power. There were no structures, systems or components out of service that contributed to this event.

Description of the Event

On Sunday October 15, 2006, at 08:46 hours, Operations was performing the weekly High Pressure Coolant Injection (HPCI) (EIIS:BJ) Turbine Hydraulic Operability Check (RT-6-055-340-2).

The test directed the operator to start the HPCI auxiliary oil pump and verify that the HPCI turbine control valve (FV-56-211) (EIIS:SCV) opens. However, the control valve failed to open.

An investigation determined that the ramp generator signal converter (RGSC) (EIIS:SC) had failed. It was further identified through a review of non-alarming computer points that a step change in RGSC output occurred on October 13, 2006 at 08:05 hours. The RGSC was replaced and calibrated. HPCI was tested and returned to operable status on October 17, 2006 at 19:25 hours.

This event involved a condition that could have prevented fulfillment of the safety function for the HPCI system which is reportable per the requirements of 10CFR50.72(b)(3)(v) and 10CFR50.73(a)(2)(v). An 8-hour NRC ENS notification (EN# 42907) was completed on October 15, 2006 at 15:44 hours. This LER is being submitted pursuant to the requirements of 10CFR50.73(a)(2)(v)(D).

Analysis of the Event

There were no actual safety consequences associated with this event. The potential safety consequences of this event were minimal. Once discovered, the inoperability of the HPCI system was limited to less than 59 hours6.828704e-4 days <br />0.0164 hours <br />9.755291e-5 weeks <br />2.24495e-5 months <br />. The reactor core isolation cooling (RCIC), automatic depressurization system (ADS), residual heat removal (RHR), and core spray (CS) systems remained operable during the period that HPCI was inoperable.

The RGSC module is part of the HPCI Turbine Control system.

The RGSC module provides the turbine speed reference signal to the Electro Governor-Mechanical (EG-M) control box. The RGSC module has two basic functions: 1) The ramp generator function controls turbine acceleration during the startup transient, and 2) the signal converter function conditions the output signal from the flow controller during system operation. The same model RGSC is used in both the HPCI and RCIC systems.

A failure analysis on the RGSC module confirmed that the component output was lower than expected. The analysis determined that the failure was caused by either an intermittent connection between the Ul amplifier output and the input to amplifier U2 or an internal fault or intermittent connection in amplifier U2. The RGSC is replaced on an 8-year frequency and was last replaced in June 2002. Limerick has not experienced any prior failures of the HPCI RGSC.

Cause of the Event

The event was caused by a failure of the RGSC. This failure occurred either due to an intermittent connection between amplifiers Ul and U2 or an intermittent failure of amplifier U2, which is an RGSC board subcomponent.

Corrective Action Completed The RGSC was replaced.

Previous Similar Occurrences There were two previous similar occurrences where HPCI failed during testing. LER 1-99-008 reported a failure to start during testing due to EGR hydraulic actuator binding. LER 1­ 96-018 reported an automatic shutdown of HPCI during testing due to a loose speed sensor connector.

Component data:

System:�BJ� (High Pressure Coolant Injection System) Component: SC (Control, Speed) Manufacturer: (General Electric Company) G080 P/N (Woodward) �A9903-091 Rev.A P/N (GE) DD213A8527P002 S/N (Woodward) 1536662