United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 94-63: Boric Acid Corrosion of Charging Pump Casing Caused by Cladding Cracks

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

August 30, 1994


NRC INFORMATION NOTICE 94-63:  BORIC ACID CORROSION OF CHARGING PUMP CASING
    CAUSED BY CLADDING CRACKS


Addressees

All holders of operating licenses or construction permits for pressurized
water reactors.

Purpose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice to alert addressees to the potential for significant damage that could
result from corrosion of reactor system components caused by cracking of the
stainless steel cladding.  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

During July and August 1993 the Virginia Electric Power Company discovered
severe corrosion damage of the carbon steel casing of a high head safety
injection pump at North Anna Unit 1.  The damage was caused by cracks through
the stainless steel cladding in the pump that allowed corrosive attack by the
boric acid coolant.  The cracks were discovered when the pump was disassembled
for maintenance and rust was observed on the otherwise shiny surface of the
cladding in the discharge section of the pump.

When the licensee ground out the cracked area to repair the pump by welding,
it discovered that the boric acid corrosion had penetrated to within about
3 mm [0.125 inch] of the outside surface of the pump.  The licensee then
ground out the corroded material, producing a cavity that was approximately
64 mm long by 38 mm wide by 13 mm deep [2.5 by 1.5 by 0.5 inches].

Discussion

The damaged pump, designated the 1C pump, is one of three such pumps designed
for both emergency high head safety injection and normal charging to the
reactor vessel of each North Anna unit.  In September 1989, the licensee
discovered cladding cracking in the suction section of the Unit 1 A pump.





9408240172.IN 94-63
August 30, 1994
Page 2 of 3


This cracking resulted in boric acid attack of the carbon steel base metal.
However, the extent of the damage is not known for this pump because the
licensee replaced the pump casing with an all stainless steel casing and did
not make a detailed examination of the old casing.  In August 1993, the
licensee inspected the Unit 1 B charging pump cladding but did not discover
any deterioration in this pump.

The discovery of cladding cracks in the 1C charging pump prompted the licensee
to visually inspect the remaining stainless steel clad charging pumps at North
Anna.  In January 1994, the licensee found eight cracks that extended through
the cladding of the Unit 2 B charging pump.  Six were located in the pump
suction section and two in the pump discharge section.  Although the licensee
did not measure the damaged volume of the base metal, rust on the surface of
the stainless steel cladding indicated that base metal corrosion attack had
occurred.  After an unsuccessful attempt to repair the 2B charging pump
casing, the licensee replaced it with one made entirely of stainless steel.
In May 1994, the licensee found numerous cracks through the cladding of the
end of the Unit 2 A charging pump.  The licensee also found a large hole
(approximately 2.5 cm [1 inch] in diameter) through the cladding in the
discharge end of the pump.  The licensee decided that repairing the 2A
charging pump casing was not practical and replaced the casing with one made
of solid stainless steel.

Corrosive attack by boric acid coolant resulting from small cracks in charging
pump cladding generally proceeds relatively slowly due, apparently, to the low
temperature of the charging coolant.  However, as the experience discussed in
this notice shows, such attack can eventually lead to significant thinning of
the pump casing and possibly substantial leakage.  Since these pumps are
normally relied on for high head emergency injection, as well as normal
charging, this type of attack, if not identified, could eventually result in
the inability of the pump to perform a vital safety function in an emergency.
This experience also shows that the corrosion of the base metal due to
cladding cracks is usually relatively easy to identify through visual
inspection.

Related Generic Communications

On October 29, 1980, NRC issued Information Notice 80-38, "Cracking in
Charging Pump Casing Cladding", in which it discussed cracking  at the
transition between the pump casing barrel and the pump suction end plate in a
Zion Unit 1 charging pump.  The cracking allowed localized boric acid attack
in the base metal to a maximum depth of 1.6 mm [0.0625 inch].  The Zion
licensee replaced this pump with one that had a solid stainless steel casing.

In June 1983, the Pacific Pump Division of Dresser Industries (the vendor)
issued procedure bulletin 037-0-0104-0 listing its pumps constructed with
cladding and suggesting methods for field inspection of the pumps.  A list of
nuclear power plants with these pumps is attached.
.IN 94-63
August 30, 1994
Page 3 of 3



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 or the appropriate Office of
Nuclear Reactor Regulation (NRR) project manager.

/s/'d by CIGrimes/for


Brian K. Grimes, Director
Division of Operating Reactor Support
Office of Nuclear Reactor Regulation

Technical contacts:  John York, RII
                     (404) 331-5536

   Don Taylor, RII
   (703) 894-5421

Attachments:
1.  List of Power Plants with Pumps Identified by Dresser
2.  List of Recently Issued NRC Information Notices
.                                        Attachment 1
IN 94-63
August 30, 1994
Page 1 of 1




PACIFIC PUMP
SHOP ORDER   SERIAL NO.           USER    PLANT

B46-617    45603/04    Public Service Electric
              & Gas    Salem #1
B46-617    45605/06    Indiana & Michigan
              Electric Co.    D.C. Cook #1
B46-617    45607/08    Indiana & Michigan
              Electric Co.    D.C. Cook #2
B46-617    45609/10    Commonwealth Edison Co.    Zion #2
B46-617    45611/12    Pacific Gas & Electric
              Co.    Diablo Canyon #1
B46-617    45613/14    Public Service Electric
              & Gas    Salem #2
B46-617    45615/16    Commonwealth Edison Co.    Zion #1
B46-617    45617/18    Pacific Gas & Electric
              Co.    Diablo Canyon #2
B46-617    45619/20    Tennessee Valley
              Authority    Sequoyah #1
B46-617    45621/22    Tennessee Valley
              Authority    Sequoyah #2
B47-096    46352/53    Duquesne Light Co.    Beaver Valley #1
B47-096    46354/55/56    Southern Nuclear Co.    J. M. Farley #1
B47-096    46357/58/59    Virginia Electric and
              Power Co.    North Anna #1
B47-096    46360/61    Portland General
              Electric Co.    Trojan
B47-096    46362/63/64    Virginia Electric and
              Power Co.    North Anna #2
B47-096    46365/66/67    Kansai Electric &
              Power Co.    Takahama #1


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