Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
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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