United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 97-52: Inadvertent Loss of Capability for Emergency Core Cooling System Motors

                                 UNITED STATES
                         NUCLEAR REGULATORY COMMISSION
                     OFFICE OF NUCLEAR REACTOR REGULATION
                         WASHINGTON, D.C.  20555-0001

                                 July 17, 1997


NRC INFORMATION NOTICE 97-52:  INADVERTENT LOSS OF CAPABILITY FOR              
                               EMERGENCY CORE COOLING SYSTEM MOTORS 


Addressees

All holders of operating licenses or construction permits for nuclear power
reactors.

Purpose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice to alert addressees to loss of cooling capability for the motor of a
safety injection pump as a result of improper gasket installation and improper
reassembly of the motor cooler following corrective maintenance.  It is
expected that recipients will review the information for applicability to
their facilities and consider actions, as appropriate, to avoid similar
problems.  However, suggestions contained in this information notice are not
NRC requirements; therefore, no specific action or written response is
required.

Description of Circumstances

On October 15, 1996, the licensee for Vogtle Electric Generating Plant noted
that there was no cooling water flow to the inboard heat exchanger for the
Unit 1, train B safety injection pump (SIP) motor cooler.  The licensee also
found that the cooling water flow to the motor cooler's outboard heat
exchanger was significantly reduced.  With the reduction in motor cooling
capacity, the train B SIP would have been unable to perform its intended
safety function during a postulated design-basis accident [medium break loss-
of-coolant accident (LOCA)].  Insufficient motor cooling would likely result
in motor bearing failure.

Discussion

The train B SIP, including its motor and cooler, was supplied by the
Westinghouse Corporation and consists of a 3-inch, 11-stage pump, model JHF,
manufactured by Pacific Pumps, and a 450-HP, 3547-RPM, 4000-V ac, 3-phase
electric motor manufactured by Westinghouse Electric Corporation.  The motor
cooler consists of two three-pass, cross-counterflow, finned-tube, heat
exchangers supplied by Sentry Equipment Corporation.    Figure I is a diagram
of the typical motor-cooler configuration.  Each heat exchanger has an inlet
and an outlet plenum.  The plenums have internal baffles that are oriented to
create a cross-counterflow flowpath.  Figure II is an end view of a typical
heat exchanger.  The licensee determined that the plenum gaskets were
installed backwards in the inboard heat exchanger.  

9707140293.                                                                 IN 97-52
                                                                 July 17, 1997
                                                                 Page 2 of 3


The solid cover plate to plenum gasket was installed in place of the plenum to
tube sheet gasket (with holes).

This incorrect installation blocked the cooling water flowpath.  While
reinstalling the gaskets correctly, the licensee recognized that it was
possible to install the plenum incorrectly, e.g., rotated 180 degrees around
the axis of the inlet/outlet fitting.  This orientation would cause the
cooling water flowpath to be altered from a three-pass, cross-counterflow
flowpath to a single-pass, once-through flowpath.  As a result the available
surface area for heat transfer would be decreased by two-thirds per heat
exchanger.  Figure III shows top views of heat exchangers with plenums
configured for three-pass operation and one-pass operation.  In the absence of
"match marks" or some other position indicator, an improperly oriented plenum
could remain visually undetected.

On October 24, 1996, the licensee identified two examples of heat exchanger
plenums that were incorrectly installed:  the other Unit 1 SIP train B heat
exchanger and a heat exchanger in the Unit 2 containment spray pump train A
motor cooler.  Because both Unit 1 train B SIP motor cooler heat exchanger
flowpaths were affected � the error completely blocked one flowpath and
reduced the heat transfer capability in the other � an engineering evaluation
was performed to determine the safety consequences to the plant.  On the basis
of the evaluation, the licensee determined that, with the SIP assumed to
respond for approximately 24 hours following a medium-break LOCA, the motor
bearings would have operated at elevated temperatures that could have led to
bearing failure within the first two hours.  Therefore, the pump would have
been unable to perform its intended safety function for that postulated
design-basis accident.  The engineering evaluation also contained a statement
that operating the SIP in the reduced-cooling flowpath condition could reduce
qualified life of the motor; the extent of reduction was not quantified.

It was concluded that the heat exchanger plenums and gaskets were installed
incorrectly because of inadequate maintenance procedural guidance and
insufficient knowledge of cooler component configuration.  The preventive
maintenance (PM) checklist provided with the work orders was generic in
nature.  The PM checklist for inspecting the motor coolers did not contain
specific instructions for proper plenum and gasket orientation or note the
importance of proper orientation and the possible effect of improper
orientation on plant equipment performance.

The licensee addressed this issue with corrective actions that included
development of a maintenance procedure to disassemble and reassemble motor
coolers.  The procedure includes checklists of precautions regarding
orientation of motor cooler gaskets and plenums; checklists to include taking
temperature readings of the plenums; steps for measurement of individual motor
cooler flows; and directions to "match-mark" cooler components to prevent
incorrect orientation at the conclusion of maintenance work.
.                                                                 IN 97-52
                                                                 July 17, 1997
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This information notice requires no specific action or written response.  If
you have any questions about the information in this notice, please contact
one of the technical contacts listed below.


                                               signed by S.H. Weiss for

                                        Marylee M. Slosson, Acting Director
                                        Division of Reactor Program Management
                                        Office of Nuclear Reactor Regulation

Technical contact:  Kathleen O'Donohue, RII
                    (706) 554-9901
                    E-mail:  kfo@nrc.gov

                    Malcolm T. Widmann, RII
                    (706) 554-9901
                    E-mail:  mtw@nrc.gov

Attachments:  
1.  Figure 1 - Typical Motor Cooler
2.  Figure 2 - End View of Heat Exchanger Assembly
3.  Figure 3 - Top View Heat Exchanger Assembly
4.  List of Recently Issued NRC Information Notices

Page Last Reviewed/Updated Tuesday, December 03, 2013