United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. NO 86-34: Improper Assembly, Material Selection, and Test of Valves and their Actuators

                                                          SSINS No: 6835  
                                                          IN 86-34         

                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
                    OFFICE OF INSPECTION AND ENFORCEMENT
                           WASHINGTON, DC 20555

                                May 13, 1986


Information Notice No. NO 86-34:   IMPROPER ASSEMBLY, MATERIAL SELECTION, 
                                   AND TEST OF VALVES AND THEIR ACTUATORS 

Addressees: 

All nuclear power reactor facilities holding an operating license (OL) or a 
construction permit (CP) 

Purpose: 

This notice is being issued to advise recipients of potential problems 
resulting from improper material selection and improper assembly procedures 
for safety-related power actuated valves This information is applicable to 
valves at the time of initial installation and during post-maintenance 
reassembly or test Although both the cited facilities are BWRs, it appears 
that PWRs may be equally vulnerable 

It is expected that recipients will review the information for applicability
to their facilities and consider actions, if appropriate, to determine if 
similar problems exist at their facilities However, suggestions contained 
in this notice do not constitute NRC requirements; therefore, no specific 
action or written response is required 

Description of Circumstances: 

In the recent past, River Bend and Shoreham have reported operational 
problems and structural integrity problems with safety-related valves and 
their actuators Both BWR facilities are currently in the startup and 
initial operational period and have reported significant problems with 
severe vibration of components and systems These vibrational problems 
appear to exacerbate but not directly cause the identified valve problems 

At Shoreham on September 25, 1985, when a valve in the RHR system was being 
operated from the control room, a response feedback signal was not received
Local inspection disclosed that the bolts connecting the actuator to the 
valve yoke were broken and the actuator was completely detached from the 
valve The valve was a relatively small "mini-flow" valve 

At River Bend on January 5, 1986, a similar event occurred involving a 
20-inch main feedwater system containment isolation valve 



8605090010


                                                             IN 86-34      
                                                             May 13, 1986  
                                                             Page 2 of 3   

Discussion: 

Licensee evaluation efforts at River Bend disclosed that manufacturer's 
instructions on actuator valve assembly were generally vague and sometimes 
the information furnished by the actuator manufacturer was contradictory to 
that supplied by the valve supplier The 20-inch valve at River Bend has a 
Limitorque SMB-4 actuator on a Velan valve The mounting capscrews are 1 
1/4-inch diameter, high strength steel, threaded into the 35,000 psi 
strength cast iron actuator housing The valve manufacturer specified 
assembly torque of 1270 ft-lb The installed bolts did not have the normally 
specified 1 1/2 diameters thread engagement, and as part of the failure 
analysis, the licensee calculated that the preload stress on the engaged 
cast iron threads would approximate the specified ultimate strength of the 
cast iron The failure which allowed the actuator to become detached was the 
capscrews tearing out of the cast iron Subsequently the licensee, the valve 
supplier, and the actuator supplier agreed that a proper installation torque 
for the valve-actuator combination would be 700 ft-lb 

During reassembly of the 20-inch valve at River Bend, the licensee 
discovered that the mating flanges did not come together at the specified 
700 ft-lb torque value Review of the actuator vendor installation and 
maintenance instructions disclosed a caution that final assembly torque 
should be applied with the valve stem at about midstroke If the valve is 
closed, the bolt preload may be transferred through the stem to the valve 
disc When the valve is next opened, the bolts are relaxed and have low (or 
no) preload Such a condition, particularly in the presence of high 
vibration, will cause early fatigue failure of the bolts 

Examination and testing of other valve assemblies at these sites showed some
with very high torque levels and others where some of the capscrews were 
found to be broken The failures appeared to be caused by overload on some 
mild steel, low strength bolts or fatigue for higher strength bolts In some
cases it appears that bolting material specifications were missing or not 
adhered to Material traceability problems with bolts and other fastenings 
are discussed in Information Notice No. 86-25, "Traceability and Material 
Control of Material and Equipment, Particularly Fasteners" River Bend and 
Shoreham have established specific programs to ensure that in the future 
proper bolts are used and are properly torqued 



                                                             IN 86-34    
                                                             May 13, 1986 
                                                             Page 3 of 3 

No specific action or written response is required by this information 
notice If you have any questions about this matter, please contact the 
Regional Administrator of the appropriate regional office or this office 


                                   Edward L Jordan, Director 
                                   Division of Emergency Preparedness 
                                     and Engineering Response 
                                   Office of Inspection and Enforcement 

Technical Contact:  James B Henderson, IE 
                    (301) 492-9654 

Attachment:    List of Recently Issued IE Information Notices

Page Last Reviewed/Updated Tuesday, November 12, 2013