Information Notice No. 81-33: Locking Devices Inadequately Installed on Main Steam Isolation Valves

                                                           SSINS No.: 6835 
                                                           Accession No.: 
                                                           IN 81-33  

                                UNITED STATES
                           WASHINGTON, D.C. 20555 
                              November 9, 1981 

                                   MAIN STEAM ISOLATION VALVES 

Description of Circumstances: 

During recent NRC inspections at the Grand Gulf Nuclear Station, Unit 1 
(Mississippi Power and Light Company), and Hartsville No. A1 Nuclear Plant 
(Tennessee Valley Authority), 26" Main Steam Isolation Valves (B21-FO22 and 
B21-FO28) manufactured by Atwood and Morrill Company, Inc., were inspected 
and were found to be deficient in installation of the locking plates. 

These valves are fitted with locking plates which prevent rotation of 
hexagonal nuts caused by vibration after they are tightened to the studs 
(part no. 26 Figure No. 1).  A tab of the locking plate is bent during 
installation to engage the flats of the hexagonal nuts (Figure No. 1, part 
nos. 26, 28 and 33).  The purpose of these studs is to couple the shaft from
the air operator to the valve stem.  Failure to bend these locking plates 
properly around the hexagonal nuts could cause the stroke of the valve stem 
to be lengthened resulting in the inability to properly open or close the 

At the facilities mentioned above, these locking plates failed to engage the
flat of the hexagonal nuts.  Since these locking plates are installed at the
manufacturer's plant, licensees have generally not been inspecting to verify
that the locking plates are installed properly.  Therefore, unless the 
licensee is required to perform valve rework on stem stroke adjustments in 
accordance with the Atwood and Morrill Instruction Manual, reverification of
the valve related work would not normally be performed. 

This Information Notice No. is provided as an early notification of a 
potentially significant matter that is still under review by the NRC staff. 
If NRC evaluation so indicates, further licensee action may be requested, In
the interim, we expect that licensees will review this information for 
applicability to their facilities.  We suggest that licensees with these 
Atwood and Morrill valves verify that the locking plates are bent 
sufficiently to engage the flats of the hexagonal nuts and perform their 
locking function. 

No written response to this information notice is requested.  If you need 
additional information, please contact the Director of the appropriate NRC 
Regional Office. 

1. Figure 1
2. Recently issued IE Information Notices


Page Last Reviewed/Updated Friday, May 22, 2015