IE Circular No. 79-04, Loose Locking Nut on Limitorque Valve Operators


                              March 13, 1979 

MEMORANDUM FOR:     B. H. Grier, Director, Region I 
                    J. P. O'Reilly, Director, Region II 
                    J. G. Keppler, Director, Region III 
                    K. V. Seyfrit, Director, Region IV 
                    R. H. Engelken, Director, Region V 

FROM:               Norman C. Moseley, Director, ROI, IE 

                    VALVE OPERATORS 

The subject document is transmitted for issuance on March  , 1979. The 
Circular should be issued to all holders of Reactor Operating Licenses and 
Construction Permits. 

Also enclosed is a draft copy of the transmittal letter. 

                                        Norman C. Moseley, Director 
                                        Division of Reactor Operations 
                                        Office of Inspection and Enforcement

1.   IE Circular No. 79-04
2.   Draft Transmittal Letter

CONTACT:  H. A. Wilber, IE 

(Transmittal letter for IE Circular No. 79-04 to each holder of an NRC 
Operating License or a Construction Permit) 


The enclosed IE Circular 79-04 is forwarded to you for information. If there
are any questions related to your understanding of the suggested actions, 
please contact this office. 

                                        (Regional Director) 

IE Circular No. 79-04 

                              UNITED STATES 
                          WASHINGTON, D.C. 20555 
                              March 16, 1979 

                                                      IE Circular No. 79-04 


Description of Circumstances: 

On December 8, 1978, Fort Calhoun Station Unit No. 1 reported that 30 out of
65 Limitorque Type SMB valve operators did not have the locking nut fastened
securely in accordance with the manufacturer's recommendation. If this 
locking nut is not secure it can loosen and allow the stem nut to move 
axially to the point that the splines are disengaged; resulting in a loss of
drive to the valve stem. The licensee reported that several locking nuts 
were slightly loose but in no instance had the stem nut backed out enough to
affect the operation of the valve. This licensee was made aware of the 
potential problem by a letter of July 28, 1978, from the NSSS supplier, 
Combustion Engineering, inc. 

Other plants have reported similar findings. On April 27, 1977, Davis-Besse 
Nuclear Power Station Unit No. 1, reported that two valve operability 
failures had been caused by locking nuts loosening and falling off. During 
the ensuing inspection program a total of 65 out of 144 safety related valve
operators required staking. Arkansas Nuclear One (ANO), Unit 2, reported on 
June 29, 1978, that several valve operators required staking. A subsequent 
inspection at ANO Unit 2 was made by an IE inspector who identified records 
that 15 out of 17 SMB operators provided by the NSSS supplier (Combustion 
Engineering Inc.) required staking. Valve operability failures, resulting 
from loosened locking nuts, have also been reported by Cooper Nuclear 
Station (Unusual Event Report 75-5), Browns Ferry Unit 2 report of March 6, 
1974 and Three Mile Island Nuclear Station Unit 1 reports of March 13, 1976 
and October 20, 1976. The corrective action by the licensee in each case was 
to stake the locking nut. 

In June 1978, the Limitorque Corporation issued a supplement to the October 
1977 issue of the Type SMB Instruction and Maintenance Manual SMBI-170 that 
called for the crimping or staking of the locking nuts. The 1971 issue of 
the manual had statements for crimping and staking of the lock nuts 
incorporated into the manual. The stem nut specification drawing provided by 
Limitorque for Unit Types SMB-000, SMB-00, SMB-0, SMB-1, SMB-2, SMB-3, and 
SMB-4 directs the customer to a Limitorque 

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IE Circular No. 79-04                                       March 16, 1979 

Drawing No. 21-497-0009-3 for instructions on staking the locking nut; the 
specification drawing for the SMB-5 unit has a reference to Limitorque 
Drawing No. 21-497-0010-3 for staking instructions. 

Pennsylvania Power and Light Company (PP&L) informed the NRC that the 
generic problem of failure to stake locking nuts exists with Limitorque Type 
SMC valve operators and Type SMB operators. PP&L Co. was advised of the 
problem by Bechtel Corporation. The information was submitted to the NRC on 
March 2, 1979 as a deficiency at the Susquehanna Steam Electric Station. The 
Type SMC Instruction and Maintenance Manual SMCI-04-78 and Drawing No. 
21-497-0013-3 provide directions for securing the locking nut. 

All holders of construction permits and operating licenses should be aware 
that the potential for valve operator failure exists if the locking nut is 
not adequately secured. The recommended action is to survey all installed 
Limitorque Operator Types SMB-000 through SMB-5 and Type SMC to determine 
that the locking nut is secure and to verify that assembly and maintenance 
instructions contain directions for securing the locking nut either by 
staking, per the vendor's recommendation, or another acceptable manner. 

No written response to this Circular is required. If you require additional 
information regarding this subject, contact the Director of the appropriate 
NRC Regional Office. 

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