United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 84-79: Failure to Properly Install Steam Separator at Vermont Yankee

                                                          SSINS No.: 6835  
                                                          IN 84-79         

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

                              November 5, 1984 

Information Notice No. 84-79:   FAILURE TO PROPERLY INSTALL STEAM 
                                   SEPARATOR AT VERMONT YANKEE 

Addressees: 

All boiling water reactor (BWR) facilities holding an operating license (OL)
or a construction permit (CP). 

Purpose: 

This information notice is being provided as a notification of a potentially
significant problem pertaining to the failure to properly install the steam 
separator while reassembling the reactor internals following a refueling and
maintenance outage. It is expected that recipients will review this notice 
for applicability to their facilities and consider actions, if appropriate, 
to preclude a similar problem from occurring 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: 

On September 11, 1984, having withdrawn control rods to the 100% power 
pattern, Vermont Yankee proceeded to increase power from 88% by increasing 
recirculation flow. In the 94-96% power range, the increase in recirculation
flow did not result in the expected increase in power. Instead, the 
power-to-flow relationship departed from a linear relationship in a step 
decrease in this range and resumed linearity above it. Also, the temperature
in the annulus area was 2 to 3 degrees hotter than normal. On September 16, 
1984, the licensee notified the NRC that licensee personnel were 
investigating the possibility that the steam separator (also called shroud 
head) lifted during high core flow. The plant A was shut down on September 
18, 1984, to determine the condition of the separator. 

The holddown bolts were inspected using an underwater TV camera and found to
be oriented properly, but not tightened. Gaps from 1/4 to 5/8 inch existed 
between the tee-bar and the clips on the shroud (see Figure 1). The steam 
separator was removed and the shroud flange was examined for damage. No 
damage was found. Internals were reassembled using procedures that emphasize
steps necessary to verify proper installation of the steam separator and 
dryer. 



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                                                          IN 84-79         
                                                          November 5, 1984 
                                                          Page 2 of 2      

The steam separator is installed by placing it in position on the shroud. A 
special tool, (see Figure 2) is used to turn the locator handle to orient 
the tee-bars tangent to the shroud. The tee-bars are then snugged up to the 
clips on the shroud by depressing the keeper nut and turning the wrench 
handle to rotate the tensioning nut. In the case of Vermont Yankee, the 
second operation was begun but not completed, leaving the gaps that were 
observed. The possibility exists that extensive operation at high enough 
power to cause the separator to lift would cause damage to the mating 
surfaces of the shroud and steam separator by battering or steam erosion; 
however, this was not observed at Vermont Yankee. If damage had occurred to 
the mating surfaces such that repair was necessary to prevent escalation of 
the damage, such repairs would require an extended outage and would likely 
result in large exposures to the maintenance work force. This would be 
inconsistent with ALARA principles. 

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


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

Technical Contact:  Mary S. Wegner, IE 
                    (301)492-4511 

Attachments: 
1.   Figure 1, Steam Separator, and Figure 2, Steam Separator Bolt Wrench 
2.   List of Recently Issued IE Information Notices 
Page Last Reviewed/Updated Tuesday, November 12, 2013