United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 90-73: Corrosion of Valve-To-Torque Tube Keys in Spray Pond Cross Connect Valves

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

                              November 29, 1990


Information Notice No. 90-73:  CORROSION OF VALVE-TO-TORQUE TUBE 
                                   KEYS IN SPRAY POND CROSS CONNECT VALVES


Addressees:

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

Purpose:

This information notice is intended to alert addressees to possible problems 
related to the corrosion of valve-to-torque tube keys in submerged valve 
applications.  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 do not constitute NRC requirements; therefore, no 
specific action or written response is required. 

Description of Circumstances:

On May 25, 1990, the Arizona Public Service Company (APS) submitted a 
10 CFR Part 21 report to the NRC regarding the misapplication of materials 
in the manufacture of the manual cross connect valves for the essential 
spray pond at its Palo Verde Nuclear Generating Station, Units 1, 2, and 3.  
APS reported that during the investigation into the cause of the failure of 
a Unit 1 essential spray pond cross connect valve, personnel discovered that 
the key that connects the valve stem to the torque tube (coming from the 
handwheel) was missing.  Each unit at Palo Verde has two such cross connect 
valves, and APS proceeded to inspect the other five valve keys.  They found 
that four of the keys had significant corrosion and that the fifth key (for 
a Unit 2 valve) was missing.

The corrosion resulted from a misapplication of material by the 
manufacturer.  The keys were manufactured from a carbon steel material that 
is susceptible to corrosion when exposed to water for extended periods of 
time.  Two of the keys had corroded away completely, while the others had 
degraded significantly.  The valves are 10-inch series 1400 butterfly valves 
supplied by the Henry Pratt Company.




9011260010 
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                                                       IN 90-73
                                                       November 29, 1990
                                                       Page 2 of 2


Discussion:

The essential spray ponds at Palo Verde provide the ultimate heat sink for 
engineered safety features and safety-related components during normal 
shutdown or accident conditions.  Each unit has two spray ponds with two 
valves that cross connect them.  One of these two valves must be opened 
during a loss-of-coolant accident to provide sufficient water inventory to 
remove decay heat for 27 days without water makeup.  If APS had not 
discovered the degraded condition of the remaining valve keys, additional 
corrosion could have prevented the operation of both cross connect valves 
for one or more of the units.

APS purchased the valves at Palo Verde specifically for the spray ponds, and 
the bid specification clearly stated that the valves would be submerged.  
Therefore, APS was unaware that the valves contained carbon steel which 
corrodes in the spray pond environment.  Before the failure, the corrosion 
problem was not apparent through visual inspection or performance.  To 
discover the problem, APS had to remove the valves from the pond and 
disassemble them.  Valves that were partially corroded continued to function 
normally.  APS replaced all six valve keys with stainless steel keys and 
developed a preventive maintenance task to periodically inspect and 
lubricate the operators for the essential spray pond cross connect valves 
during refueling outages.  APS reviewed all Henry Pratt valves supplied to 
them for underwater service and identified no other deficiencies.  In 
addition, APS will perform an engineering review of components exposed to 
chemistry similar to the spray pond water to ensure that a similar condition 
does not exist elsewhere.

The staff contacted other licensees having plants that use spray ponds, and 
they all indicated that their valves were kept in dry pits and were 
therefore protected from corrosion (in addition to being more accessible for 
inspection and maintenance).  However, the situation encountered at Palo 
Verde is not necessarily limited to just spray pond environments.  The 
operating parts of any valve used in a submerged application could be 
susceptible to corrosion if improper materials are used.  The experience at 
Palo Verde indicates that even valves specifically purchased for submerged 
use can contain inappropriate materials.

This information notice requires no specific action or written response.  If 
you have any questions about the information in this notice, please contact 
the technical contact listed below or the appropriate NRR project manager.




                              Charles E. Rossi, Director
                              Division of Operational Events Assessment
                              Office of Nuclear Reactor Regulation

Technical Contact:  David Terao, NRR
                    (301) 492-3317

Attachment:  List of Recently Issued NRC Information Notices
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