Why Are Zirconium Bars Ultrasound Abnormalities?

In response to the current phenomenon of ultrasonic exceedances in the zirconium bar alloy of black zirconium wedding rings, tests were carried out using ultrasonic testing, radiographic testing, low magnification tissue, and metallographic analysis. The results show that a single ultrasonic signal was found along the length of the zirconium bar by ultrasonic inspection, which was a single point and no coherent exceedance was found. The radiographic method revealed dot-like morphology that was clearly visible in the negatives. The results of the low magnification tissue examination of the zirconium alloy indicated the presence of foreign inclusions in the zirconium rods. The metallographic organization of the outer and inner layers of the zirconium alloy rod specimen was grade 11.5. No abnormal coarse grain organization was found, and the effect of coarse grain organization on the zirconium alloy can be excluded.

1. Introduction

Zirconium and zirconium alloy rods are widely used as upper and lower connecting rods in nuclear reactors because of their excellent thermal neutron cross-sectional absorption rate and good corrosion resistance. Zirconium alloy ingots are forged, extruded, and rolled in sequence to produce the finished product. In order to ensure the safety and quality of nuclear reactors. In order to ensure the safety and quality of nuclear reactors, zirconium alloy products are inspected and judged by means of ultrasound, eddy current, penetration, radiography, and surface inspection during industrial production in nuclear power plants. In order to analyze the causes of the ultrasonic exceedance phenomenon, a research experiment is carried out on the exceedance bars to provide a theoretical and practical basis for controlling the quality of zirconium alloy bars.

2. Experimental orientation

Each zirconium alloy bar was first subjected to radiographic and ultrasonic inspection, followed by low magnification tissue scraping and optical microstructure metallographic analysis of the defective zirconium gold bars. In order to avoid breaking the surface morphology of the group of defective products, the metallographic organization was observed layer by layer to observe the morphology of the defects.

3. Ultrasonic examination results

The ultrasonic mapping of the zirconium alloy rods containing the defects showed a single ultrasonic signal along the length of the zirconium rod, which was a single point, and no coherent exceedance signal was found. In addition, the signal persisted when the angle of the zirconium bar was rotated, and it is tentatively assumed that the bar signal is an inclusion. Ultrasonic, radiographic, low magnification and metallographic observation methods were carried out to investigate the phenomenon of abnormal ultrasonic signals in the produced zirconium alloy rods, and the results showed that: 

(1) A single ultrasonic signal was found to be present along the length of the zirconium rods by ultrasonic inspection. 

(2) The radiographic inspection method revealed dot-like morphology clearly visible in the negatives. 

(3) The results of the zirconium alloy low confidence tissue examination indicated the presence of foreign inclusions in the zirconium rods. 

(4) The metallographic organization of the outer and inner layers of the zirconium alloy bar specimens was 11.5 grade. No abnormal coarse grain organization was found, and the effect of coarse grain organization on the zirconium alloy can be excluded.