[en] The program was performed to provide sufficient fracture toughness data for typical production heats of HTGR materials to determine the adequacy of the KIR curve for HTGR applications. The HTGR test program included mechanical tests such as tensile, drop weight-NDTT, Charpy V-notch, instrumented precracked Charpy, static and dynamic compact fracture, and dynamic three-point bend tests. Five heats of HTGR materials were tested over the temperature range of -200 F to +550 F. The HTGR materials studied were a A508-1 forging, A537-1 and A537-2 plates, and a manual metal arc weldment in A537-2 plate (both weld metal and heat-affected zone). Mill test reports and welding history, metallography, chemistry, archive and specimen drawings are included. All fracture toughness data generated for the HTGR materials fell above the KIR curve, except at very low temperatures which are not representative of service conditions. For all of the HTGR materials studied except the A508-1 forging material, the KIR curve appears to be too conservative