United States Nuclear Regulatory Commission - Protecting People and the Environment

ACCESSION #: 9503160186

                            January 19, 1995

No: 95-01                TECHNICAL ISSUE SUMMARY           Date: 1/10/95


PROBLEM:  At Calvert Cliffs Unit 2, the 22 auxiliary feedwater (AFW) pump
turbine governor valve stem has repeatedly bound since November 1993. 
Corrosion products from galvanic and crevice-corrosion caused the stem to
bind in the packing gland area.  The first stem to bind had been in
service for 17 years.  However, the last two stems that failed had been
in service for approximately three months.  Examination of the failed
stems showed a significant difference in stem surface hardening depending
on when the stem was procured.

EVALUATION:  Both Calvert Cliffs units have two turbine driven AFW pumps. 
The turbines were manufactured by Terry Steam Turbine Company.  Dresser-
Rand is the AFW turbine vendor.  The stem is type 410 stainless steel that
has a hard nitrited surface layer.  The packing gland consists of
alternating series of carbon spacers and stainless steel washers.  Until
May 1994, all the governor valve stems had been in service over 17 years. 
However all the stems were scheduled for replacement based on industry
recommendations they received in 1993.

The problem first occurred in November 1993 when the 22 AFW pump turbine
tripped on overspeed during surveillance testing.  The licensee was unable
to find the cause for the overspeed and elected to implement an
accelerated test program to demonstrate operability.  Following five
successful tests the licensee resumed their normal test schedule.  On the
next test performed in May 1994, the turbine tripped again on overspeed. 
Examination of the governor found corrosion of the stem in the area where
the stem interfaces with the packing gland.   The licensee replaced the
stem with a new stem that was procured in 1989.  They inspected the other
valve stems and found no evidence of corrosion.  They also concluded that
the accelerated test program masked the binding problem.

In September 1994, the governor valve failed to move during a routine
surveillance test.  The licensee contracted with a company that
specializes in failure analysis (Failure Prevention & Investigation
International).  By electron microscopic examination, they concluded that
the new governor valve stem was metallurgically inferior to the original
stem that had been in service for 17 years.  The protective coating on the
newer stem was essentially nonexistent while the old stem had a well
formed hard overlay.  They concluded that the protective coating on the
old stem, even in the pitted areas, had restricted stem corrosion to
shallow areas that had not penetrated into the base metal.  The slower
corrosion rate on the original stem allowed corrosion product build up to
be cleared off of the stem during routine pump testing before it could
fill the annulus between the stem and the packing gland and restrict the
operation of the valve.

At least three contributing causes have been identified.  The vendor had
reduced hardness design specification three times since the turbine was
first procured.  Also, the licensee discovered dissimilar metals in the
packing gland and sulfur impurities in the carbon

spacers.  They found 15 of the 21 packing gland washers were type 300
stainless, instead of the type 400 specified by the vendor.  The vendor
had supplied the washers as a set.  Examination of washer sets in the
licensee's inventory found a mix of material in every set.  This
difference in the metal material, in conjunction with some sulfur
impurities in the carbon spacers, resulted in galvanic corrosion.  The
governor valve stem was replaced with a spare purchased in 1989, and the
packing gland was reassembled using only type 400 stainless steel.

Following the September failure the licensee began exercising the governor
valves of all four turbines every four days by disconnecting the governor
valve stem from the governor linkage and verifying the governor valve stem
moved freely.  In December 1994 the licensee changed the frequency to once
every week.  On January 4, 1995, during the weekly exercise activity, the
22 AFW governor valve stem was bound and required the use of a rubber
mallet to free it.  Examination of this stem revealed similar corrosion
of the stem.  This stem was replaced with a new stem that was also
procured in 1989.  The licensee changed the 22 AFW governor valve stem
exercise cycle back to every four days.

LICENSEE/VENDOR ACTION:  The licensee resumed the exercising of the 22 AFW
pump governor valve on a four day cycle.  The other AFW governor valve
stems continued to be exercised on a weekly basis.  They also made a
preliminary 10 CFR Part 21 report on November 15, 1994.  In addition, the
licensee is working with the vendor to procure new "super alloy" corrosion
resistant valve stems.  Plans to replace the other AFW pump turbine
governor valve stems during the pumps' overhaul cycle were put on hold.

NRC CONTACTS:  Region I is forwarding this summary to NRR for a review of
generic implications and to Region I inspectors for site-specific

CONTACTS:  Peter Wilson (410) 586-2626   Larry Doerflein (610) 337-5378

REFERENCES:  NRC Inspection Report 50-317/94-29; 50-318/94-28

                               Original Signed by:

                               Donald R. Haverkamp 
                               Technical Assistant 
                               Division of Reactor Projects


Distribution:  (VIA E-MAIL)
T. Martin, RA
W. Kane, DRA
W. Dean, OEDO
J. Zwolinski, NRR
L. Marsh, NRR
D. McDonald, NRR
F. Gillespie, NRR
B. Grimes, NRR
A. Chaffee, NRR
B. Sheron, NRR
R. Wessman, NRR
R. Spessard, NRR
R. Gallo, NRR
S. Black, NRR
W. Haass, NRR
L. Shao, RES
E. Jordan, AEOD
E. Merschoff, RII
E. Greenman, RIII
A. Beach, RIV
R. Cooper, DRP
W. Lanning, DRP
J. Wiggins, DRS
A. Blough, DRS
W. Hehl, DRSS
S. Shankman, DRSS
DRS Section Chiefs
DRP Staff
D. Screnci, PAO

*See previous concurrences
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OFFICE     *RI/DRP        *RI/DRP        *RI/DRP        RI/DRP
NAME       LDoerflein/LTD CCowgill/CJC   DHaverkamp/DRH RCooper/RWC
DATE       01/11/95       01/11/95       01/17/95       01/19/95
                          OFFICIAL RECORD COPY


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