INVESTIGATION INTO HYDRIDE REORIENTATION IN DUMMY FUEL ROD CLADDING (Zr-1%Nb) UNDER INTERNAL PRESSURE DURING TESTING SIMULATING SNF HANDLING AND ACCIDENTS WITH LIMITING CLADDING HEATING UP TO 410 °С

This paper presents the results of experimental investigations into hydride reorientation that (HRT) can occur in fuel rod claddings under conditions simulating normal and some accident SNF handling modes with limiting cladding heating up to 410 C. Dummy fuel rods with Zr-1%Nb cladding with different hydrogen content under internal pressure (cold pressure under cladding of 3, 4, and 5 P) were subjected to testing with heating up to 410 , holding at this temperature during 8 h and subsequent cooling. It was found that at a hydrogen concentration of 400 ppm, intensive hydride reorientation in the dummy fuel rod claddings during thermal test begins at a tangential stress of 5560 MPa at 410 C. As the hydrogen concentration decreases, the intensity of test impact on hydride reorientation decreases significantly. SNF thermal cycling and holding in DSFSF significantly increases hydride reorientation. In the claddings with a 400 ppm hydrogen concentration subjected to 3 thermal cycles 180410 C, almost complete hydride reorientation occurs. Mechanical testing of samples with different hydrogen content was conducted before and after the hydride reorientation test.