United States Nuclear Regulatory Commission - Protecting People and the Environment

Bulletin 78-10: Bergen-Paterson Hydraulic Shock Suppressor Accumulator Spring Coils

                               UNITED STATES 
                       NUCLEAR REGULATORY COMMISSION 
                    OFFICE OF INSPECTION AND ENFORCEMENT 
                          WASHINGTON, D. C. 20555 
                                     
                               June 27, 1978  

                                                     IE Bulletin No. 78-10 

BERGEN-PATERSON HYDRAULIC SHOCK SUPPRESSOR ACCUMULATOR SPRING COILS 

Description of Circumstances: 

During the conduct of hydraulic shock suppressor (snubber) functional 
testing and seal replacement programs at several licensed facilities, a 
number of broken accumulator spring coils have been found in early model 
Bergen-Paterson hydraulic snubbers. The attached extract from a Bergen-
Paterson advisory letter, dated April 6, 1978, states that a broken 
accumulator spring alone would not render the snubber incapable of 
performing its design function; however, the broken spring could cause 
internal damage to the accumulator which could result in unit inoperability.

The subject snubbers are of the external pipe design with serial numbers 
487,000 to 515,000 and F60,635 through F75,000. The accumulator springs in 
these snubbers are basically carbon steel and were coated with a 
petro-chemical rust preventative by the vendor. Despite this initial 
protective coating, those springs found broken exhibited advanced stages of 
corrosion. The factors which caused the spring corrosion are undetermined. 

Bergen-Paterson has recommended that corrosion susceptible accumulator 
spring coils be replaced with teflon coated or stainless steel coils during 
the next refueling shutdown. 

Action to be Taken by Licensees: 

For all power reactor facilities with an operating license or a construction
permit: 

1.   If you have received the enclosed Bergen-Paterson letter addressing the
     accumulator spring problem, and if you have those units installed or in
     ready spares at your facility, it is requested that you describe what 
     corrective action you have taken or plan to take to assure that the 
     operability of snubbers in safety related systems is not impaired. It 
     is also requested that you describe the condition of any springs that 
     were observed during the performance of the corrective action. 



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IE Bulletin No. 78-10                                       June 27, 1978 

2.   If you have not received the enclosed Bergen-Paterson letter, it is 
     requested that you describe what action you plan to take if the subject
     snubbers are installed or in ready spares at your facility to assure 
     that the operability of snubbers in safety related systems is not 
     impaired. 

3.   If the snubbers are currently installed in safety related systems, it 
     is requested that you identify their location in your response to this 
     bulletin. 

4.   Report in writing within 45 days for facilities with an operating 
     license and within 60 days for facilities with a construction permit, 
     your plan of action and schedule with regard to Items 1, 2 and 3. 
     Reports should be submitted to the Director of the appropriate NRC 
     Regional Office and a copy should be forwarded to the NRC Office of 
     Inspection and Enforcement, Division of Reactor Operations Inspection, 
     Washington D. C. 20555. 

Approved by GAO, B180225 (R0072); clearance expires 7-31-80. Approval was 
given under a blanket clearance specifically for identified generic 
problems. 

Attachment:
Extract from Bergen-Paterson 
  letter dated April 6, 1978



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                                 Attachment 
                                     
                Extract from Bergen-Paterson Advisory Letter

                                            SUBJECT:B/P Hydraulic Snubbers 
                                                    HSSA Accumulator Spring
                                                    Advisory Letter        

Gentlemen: 

Bergen-Paterson advises that broken accumulator spring coils have been found
in a number of early model hydraulic snubbers at the time when units were 
being dissembled for seal replacement purposes. The early models noted are 
identified as being the external pipe design having serial numbers between 
487,000 and 515,000 and F60,635 through F75,000. These units were initially 
furnished with music wire or chrome silicone spring material both coated 
with a rust preventative. All later external pipe design units were 
initially furnished with springs having the same material as noted above; 
however, all coils were teflon coated. Our current model units are furnished 
with stainless steel coils. Both the teflon coated and stainless coils have 
been found to give satisfactory service. 

It is specifically pointed out that a unit remains functional even with a 
broken spring; however, the possibility does exist that the debris from a 
broken spring coil could in fact cause damage to the Accumulator Piston 
U-Cup Seal resulting in possible leakage of fluid. The remote possibility 
for the Accumulator Piston to become jammed in the tube also exists 
although, however, this has not been experienced. 

Bergen-Paterson has issued this advisement to make users aware of the 
possibility of broken accumulator springs and recommends that units having 
uncoated coils be refitted with either teflon coated or stainless steel 
coils at the next refueling shutdown. 

                                        Very truly yours, 

                                        BERGEN-PATERSON PIPE SUPPORT CORP. 

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