United States Nuclear Regulatory Commission - Protecting People and the Environment

Morning Report for March 6, 2006

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Part 21: Woodward 505 Controls manufactured between December 2003 and June 2004, P/N: 9903-543




License No:

MR Number: H-2006-0004
Date: 02/10/2006

Source Document: Letter


Woodward 505 Controls manufactured between Dec. 2003 & June 2004
P/N: 9903-543

Engine Systems Inc. (ESI) has concluded an investigation of a condition reported by Woodward for
their 505 controller. The 505 is a digital controller used to control speed of steam turbines. Only a
small number of 505 controls are utilized in nuclear service; these are identified by the "9903-" part
number prefix.

Woodward service bulletin 01365 (attached\ reports that a low voltage issue with the internal power
supply has been detected in a small population of 505 controls that have been returned for service.
This issue has been attributed to a problem with the mechanical connection between the
controller's internal fuse and the fuse clips that are installed in-line with the unit's CPU. The low
voltage condition results in a continuous reboot of the control; this causes the control's output
signal to go to zero volts. For most commercial applications, the 505 controls are configured such
that zero volts results in turbine shutdown; thus, the potential failure mode would result in a safe
shutdown of the control and the turbine (as reported in the Woodward bulletin).

For nuclear applications however, the 505 controls are configured for maximum speed at zero volts
output. This is necessary to keep the governor valve open during standby so that steam can be
admitted to the turbine by the trip and throttle valve to begin startup. Once turbine speed is
detected by the 505, it will take control and close the governor valve as necessary to maintain the
required speed setting. In this case, the potential failure mode would result in shutdown of the
control which would cause the turbine speed to abruptly increase until the overspeed device trips
and shuts down the turbine.

Apparently the following three (3) nuclear 505 controls are affected by this notification. Of these, only two (2)
were shipped for nuclear service, both to Southern Nuclear - Vogtle site.

Part No. Serial No. Customer Customer PO ESI SO
9903-543 13804744 N/A, ESI test specimen N/A 8000006
9903-543 13804745 Southern Nuclear - Vogtle 7059691 8000006
9903-543 13804975 Southern Nuclear - Vogtle 7059691 8000006

Suspect 505's should be returned to ESI as soon as possible to have the power supply module
reworked. Contact ESI's Customer Service department with the part number and serial number of
the control.

Accession Numbers:

Accession No Accession Date
ML060540188 02/10/2006


Name Office Abbrev Phone No E-Mail
TABATABAI, OMID NRR (301) 415-6616 OTY@nrc.gov
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