United States Nuclear Regulatory Commission - Protecting People and the Environment

This document is typed from a poor original 50.55(e) telephone
and fax report.

                         EVENT NOTIFICATION WORKSHEET

Notification Time:  17 May 1995 1645

Facility:           Watts Bar Unit 1

Caller's Name:      P. L. Pace

Caller's Number:         (615) 365-9266

Event Date:         16 March 1995

Regulation:         10 CFR 50.55(e)

Description:

52 of 65 incore thermocouples failed a post-HFT [hot functional
test]
insulation resistance test.  Testing by Westinghouse indicates
the failures
resulted from deficiencies in the vicinity of weld areas of the
thermocouple
sheaths.

The Incore Thermocouple Subsystem of the Incore Instrumentation
System
performs a (primary) safety function during normal and
post-accident operating
modes by providing fuel assembly coolant temperature signals to
the Inadequate
Core Cooling Monitor (ICCM).  The incore thermocouples are
located at the core
exit for each quadrant.  Core exit temperature is provided for
verification
and long term surveillance of core cooling.  Although not relied
on for
automatic actuations, the incore thermocouples are used by
operators for
actions directed by the emergency procedures.  Control room
indications are
provided through the ICCM plasma display which is the primary
indication used
by the operator during an accident.  Core exit temperature is
also used for
unit stabilization and cooldown control.

Because of the unique design for the specific application, the
deficiency is
considered limited to the unit 1 and unit 2 incore thermocouples. 
The unit 1
incore thermocouples are being replaced.  Westinghouse will
prepare a report
to aid TVA in determining if further corrective actions are
required.

Reference:  WBPER950167
              CDR 95-04
Page Last Reviewed/Updated Thursday, March 29, 2012