Ultrasonic determination of module form, size, and distribution in ductile cast iron

The purpose of this program is to support the Electric Power Research Institute (EPRI) in developing a qualification program for nodular cast iron as an economical material for the fabrication of dual-purpose storage/transport containers for nuclear spent fuel. The ductility of nodular cast iron is directly linked to the form, size, and distribution of graphite and the purity of the ferritic microstructure. Therefore, an integral part of the qualification program is to develop a reliable nondestructive test method for measuring these parameters. An extensive literature search was done to assist in developing the technical basis for laboratory measurements. The most relevant works are shown in the bibliography of this report. EPRI supplied various nodular cast iron specimens from different manufacturers. Samples were made from these specimens and evaluated in the laboratory using pulse-echo ultrasonic techniques. The measurements included bulk velocity, attenuation, and frequency spectrum. Preliminary experimental results show that the diameter of scattering centers can be estimated by measuring material attenuation versus frequency in the range from 7 to 12 MHz. Factors contributing to the precision of these measurements were identified. Improved precision is expected using frequencies above 12 MHz. Specimen coupons were marked, prepared, and sent to an independent laboratory for comprehensive metallographic analyses. Additional tasks in this program included supporting EPRI and ASTM in developing an industry specification for nuclear spent fuel transport containers fabricated with ductile cast iron. This consisted of preparing the first draft of a supplemental NDT procedure, attending and presenting a report at a committee meeting, and writing a technical note for distribution to ASTM committee members