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Forensic Analysis of CANDU Fueling Machine Clutch Plate

In-depth examination and analysis of CANDU component

Project objective

A CANDU operator experienced problems with a fueling machine clutch plate assembly.  Four retaining screws fractured, rendering the clutch on the charge tube external drive inoperable. The client sent the damaged clutch plate assembly to Kinectrics requesting a forensic evaluation to determine the cause of the failure.

Scope of work

The clutch assembly was radiologically contaminated and was examined in Kinectrics’ zoned metallurgical laboratory. Kinectrics' Radioactive Materials Laboratory offers a full range of metallurgical sample preparation and analysis capabilities, including optical and scanning electron microscopes for detailed examination of fracture surface features. Failed components can be safely examined in the ‘as-found’ condition (i.e., prior to decontamination), ensuring that all relevant forensic information is captured during the analysis.   
 
Test results
 
Failure of the clutch gear retaining screws was caused by high cycle fatigue. Multiple fatigue cracks nucleated on opposite sides of the screw threads and propagated inward under reversed bending loads.

The failures were caused by non-uniform residual stresses introduced by tack welding one side of each screw head to the clamping ring.

The tack welding procedure had been recently introduced to prevent the retaining screws from backing out of the assembly if they became loose.he failures were caused by non-uniform residual stresses introduced by tack welding one side of each screw head to the clamping ring. The tack welding procedure had been recently introduced to prevent the retaining screws from backing out of the assembly if they became loose.  As a result of the Kinectrics analysis, the client discontinued using the tack welding procedure.

 

 

 

 

 

 

 

 

 

 

About This Case Study

Industry Sector

  • Generation

Generation Type

  • Nuclear

Nature of Service

  • Inspection
  • |
  • Analysis

Client Assets

  • Fuel Channels

Kinetrics Facilities

  • Radioactive Materials Laboratory
  • |
  • Materials Testing and Structural Integrity

Tags

  • metallurgical
  • |
  • Fueling
  • |
  • CANDU
  • |
  • Failure Analysis
  • |
  • Forensic examination