Information Notice No. 88-85: Broken Retaining Block Studs on Anchor Darling Check Valves
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
October 14, 1988
Information Notice No. 88-85: BROKEN RETAINING BLOCK STUDS ON
ANCHOR DARLING CHECK VALVES
Addressees:
All holders of operating licenses or construction permits for nuclear power
reactors.
Purpose:
This information notice is being provided to alert addressees to potential
prob-lems relating to the failure of retaining block studs on Anchor Darling
check valves and the possible generic implications. Diablo Canyon, Unit 2,
and D.C. Cook Units 1 and 2, have recently reported problems with this type of
failure. 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:
In October 1988 at Diablo Canyon, Unit 2, a scheduled preventative maintenance
performed on a check valve in the Residual Heat Removal (RHR) System revealed
that two retaining block studs (see drawing) were completely broken. This
valve had been successfully stroked by hand several times before the mechanic
detected slight movement of the retaining block. Upon further investigation
the mechanic discovered that the studs were actually broken. The valve is an
8-inch pressure isolation valve in piping attached to the Reactor Coolant
System hot leg. One stud was sheared at the block to valve body interface and
the other stud was broken off inside the retaining block. There were signs of
significant corrosion product build-up on the failed studs. The valve was
manufactured by Anchor Darling.
Discussion:
The licensee has taken actions to repair the RHR valve, and a metallurgical
evaluation of the failed studs is underway. The companion valve for the other
RHR loop valve at Diablo Canyon, Unit 2, has been disassembled and found to be
acceptable. The licensee has also disassembled eight 10-inch Anchor Darling
swing check valves in the Safety Injection (SI) System. These valves are also
pressure isolation valves. These valves have also been found to be
acceptable. The stud material in all ten of these valves is ASTM A193 Grade
B6 Type 410 stainless steel. A discussion of problems noted with 410
stainless steel parts in other valve applications is contained in Information
Notice 85-59, "Valve Stem Corrosion Failures."
8810140212
. IN 88-85
October 14, 1988
Page 2 of 2
Several weeks prior to the failure at Diablo Canyon, Unit 2, D.C. Cook, Unit
2, discovered similar stud failures in Anchor Darling swing check valves. One
broken stud and one cracked stud were discovered in each of two 8-inch RHR low
head injection check valves. These valves are the second check valves back
from the reactor coolant loop hot legs, and they act as pressure isolation
valves. At D.C. Cook, Unit 2, there are two additional 8-inch Anchor Darling
swing check valves in the RHR system. There are also eight 10-inch Anchor
Darling swing check valves in the SI system. All four RHR valves and six of
the eight SI valves have been inspected. One of the SI accumulator injection
check valves was also found to have a cracked stud. The remainder of the
valves inspected were found to be acceptable.
At D.C. Cook, Unit 1, the two RHR injection check valves were inspected and
each was found to have one broken stud. Two SI accumulator injection check
valves were also inspected and found to be acceptable. Metallurgical
evaluation of the failed studs is ongoing with the preliminary analysis
indicating that the failures are due to intergranular stress corrosion
cracking.
Based upon discussions with the valve vendor, the NRC has learned that the af-
fected valves at the plants discussed above are Anchor Darling Model Number
S350WSC, Drawing Number 94-12892. The vendor also indicated that based pri-
marily on experience with pressure boundary bolting, they have been using Type
17-4PH stainless steel for bolts and studs in borated water service. They no
longer manufacture the S350WSC valve, and they recommend replacement studs be
made of Type 17-4PH stainless steel rather than Type 410.
The NRC staff believes that with seriously degraded studs, the retaining
blocks could be dislodged if these valves are called upon to open rapidly
during accident conditions. This could lead to blockage of the flow path, and
the valves would be incapable of reseating.
Licensees may wish to consider potential actions that would be appropriate if
one of these check valves should fail in service prior to inspection of the
studs. Such actions might include appropriate procedures and operator
training.
No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact the technical
contact listed below or the Regional Administrator of the appropriate regional
office.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contact: Ted Sullivan, NRR
(301) 492-0901
Attachments: 1. Figure of Valve
2. List of Recently Issued NRC Information Notices
. Attachment 2
IN 88-85
October 14, 1988
Page 1 of 1
LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
_____________________________________________________________________________
Information Date of
Notice No._____Subject_______________________Issuance_______Issued to________
88-84 Defective Motor Shaft 10/20/88 All holders of OLs
Keys in Limitorque Motor or CPs for nuclear
Actuators power reactors.
88-83 Inadequate Testing of Relay 10/19/88 All holders of OLs
Contacts in Safety-Related or CPs for nuclear
Logic Systems power reactors.
88-82 Torus Shells with Corrosion 10/14/88 All holders of OLs
and Degraded Coatings in or CPs for BWRs.
BWR Containments
88-81 Failure of Amp Window 10/7/88 All holders of OLs
Indent Kynar Splices or CPs for nuclear
and Thomas and Betts power, test, and
Nylon Wire Caps During research reactors.
Environmental Quali-
fication Testing
88-80 Unexpected Piping Movement 10/7/88 All holders of OLs
Attributed to Thermal or CPs for PWRs.
Stratification
88-79 Misuse of Flashing Lights l0/7/88 All holders of OLs
for High Radiation Area or CPs for nuclear
Controls power reactors.
88-69, Supp 1 Movable Contact Finger 9/29/88 All holders of OLs
Binding in HFA Relays or CPs for nuclear
Manufactured by General power reactors.
Electric (GE)
88-78 Implementation of Revised 9/22/88 All holders of OLs
NRC-Administered Requali- or CPs for nuclear
fication Examinations power reactors.
88-77 Inadvertent Reactor 9/22/88 All holders of OLs
Vessel Overfill or CPs for BWRs.
_____________________________________________________________________________
OL = Operating License
CP = Construction Permit
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