Postirradiation Examination of the Pm-3A Type 1 Serial 2 Core. Part II. Postirradiation Examination of Control Rod 6

摘要

Because of a Type 1 Serial 1 core control rod malfunction, one spent control rod from the PM-3A Type 1 Serial 2 core was examined in considerable detail. Measurements of blade configuration and dimensions showed no discernible changes except for increases in blade thickness. Blade Thickness measurements showed a 15-mil increase in blade thickness from top to bottom, suggesting that blade swelling was associated with increasing neutron dosage and probably operating temperatures. Examination of the blade microstructure showed that considerable longitudinal cracking had occurred in the Eu2O3-2TiO2- Type 304L stainless steel dispersion. These cracks were largest in the region adjacent to control rod weldments and appeared to propagate through stringers of dispersed europium titanate particles. Propagation of these cracks and possibly the formation of new cracks during reactor operation probably caused the observed increase in the thickness of the blade. Blade thickness increases were not sufficient to cause binding, as the rod moved freely in its clot. Although scale deposits were observed on the control rod, it is believed that such deposits would not interfere with control rod operation. (Author)