METALLURGICAL FAILURE ANALYSIS OF PM-3A REACTOR CONTROL ROD LIFTING KNOB.
NAVAL RESEARCH LAB WASHINGTON D C
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A metallurgical analysis has been performed upon a failed control rod cap from the Navy PM-3A Nuclear Power Plant. Material supplied to the Metallurgy Division for this investigation was the lifting knob which had separated in service from the main body of the cap. The specific objective of the analysis was to determine if the material of application met design specifications and to determine the probable cause of component failure. Compositional analysis by x-ray spectrochemical and gravimetric techniques established that the lifting knob, and thus the failed control rod cap, was fabricated from a 300 series stainless steel, not from 17-4 PH precipitation hardening stainless steel as specified. Microstructural and hardness examinations further confirmed the substitution of a 300 series stainless steel for the 17-4 PH steel composition. Examination of the stem of the control rod cap knob at which failure occurred revealed severe necking down and heavy striations corresponding to work hardening lines. This visual evidence coupled with analytical evidence of a low strength material of application suggests component failure through gross overload. Author
- Fission Reactor Materials