United States Nuclear Regulatory Commission - Protecting People and the Environment

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 
Page Last Reviewed/Updated Tuesday, November 12, 2013