Researchers at Oak Ridge National Laboratory and the U.S. ITER Project Office have developed a new cast stainless steel that is 70 percent stronger than comparable steel and is being evaluated for use in the huge shield modules required by the ITER fusion device. ITER is a multibillion-dollar international research and development project to demonstrate the scientific and technological feasibility of fusion power and to enable studies of self-heating burning plasmas. It will require hundreds of tons of complex stainless steel components that must withstand the temperatures associated with being in the proximity of a plasma heated to more than 100 million degrees Celsius.

The ITER device will be assembled in Cadarache, France, using components fabricated in the United States and in the other partner nations - China, the European Union, India, Japan, the Republic of Korea and the Russian Federation. It is based on the tokamak concept, in which a hot gas is confined in a torus-shaped vessel using a magnetic field. When operational, the device will produce some 500 MW of fusion power.

Jeremy Busby of the ORNL Materials Science and Technology Division said the ITER shield modules present a particular challenge. "The United States must produce nearly 100 of these modules that are 3-4 tons each and include geometric shapes and openings," he explained, adding that drilling holes in solid steel would result in the removal and loss of 30 percent of the material. Busby said casting the steel into a near-final shape was another alternative, but it weakens its properties.

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