United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 81-14: Potential Overstress of Shafts on Fisher Series 9200 Butterfly Valves with Expandable T Rings

                                                            SSINS No.: 6835 
                                                            Accession No.: 
                                                            8011040292     
                                                            IN 81-14       

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

                                April 7, 1981

Information Notice No. NO- 81-14:   POTENTIAL OVERSTRESS OF SHAFTS ON FISHER 
                                   SERIES 9200 BUTTERFLY VALVES WITH 
                                   EXPANDABLE T RINGS 

Description of Circumstances: 

Northern States Power Company recently informed NRC that the design of 
certain butterfly valves at Monticello Nuclear Generating Station contained 
a design error that shows the calculated maximum shaft stress to be 
underestimated. The valves affected are Fisher Controls Company Series 9200 
butterfly valves (6 to 48 inches) with expandable T rings (inflatable seals)
manufactured from 1968 to 1972. In the calculation of the shaft stress, the 
length between the shaft bushing and the attachment of the shaft to the 
valve disc used in the stress calculations was shorter than the actual 
length. From discussions with the valve manufacturer, the cause of the 
difference in the design calculation dimension and the actual dimension was 
that the shaft bushings were recessed into the valve body to accommodate the 
pneumatic passages for the inflatable seals. Evaluation of the design error 
for the valves at Monticello indicate that the maximum shaft stress in the 
closed position remains less than the minimum yield strength of the shaft 
material. The licensee intends to keep the affected valves closed while 
operating and plans to replace the shafts with ones of higher strength 
material. 

The potential consequences of the design error is that, under accident 
loading conditions, there is a possibility for excessive deformation of the 
shaft. Therefore, these valves when closed under the dynamic conditions of a 
LOCA or, if already closed, may not seal essentially leaktight. Since these 
valves are used primarily in the containment purge and vent lines, a 
substantial safety hazard would exist if these valves could not be closed or
if there was excessively leakage past these valves. Containment integrity 
therefore could not be assured. The operability of containment purge and 
vent valves is item II.E.4.2 in the TMI Action Plan. 

The facilities identified that may have the Fisher valves include Duane 
Arnold, Monticello, Palisades, Peach Bottom Units 2 and 3, and Point Beach 
Units 1 and 2. Discussions with the valve vendor indicate that the reviews 
of the valve calculations affected should be completed by mid-April. 

This information is provided as an early notification of a significant 
safety matter that is still under review by the NRC staff. It is expected 
that licensees will review the information for possible applicability to 
their plants. If NRC evaluations so indicate, further licensee actions may 
be requested. 
.

                                                             IN 81-14      
                                                             April 17, 1981 
                                                             Page 2 of 2   

No written response to this information notice is required. If you need 
additional information with regard to this matter contact the Director of 
the appropriate NRC Regional Office. 

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