Shape optimization of a torus seal under multiple loading conditions based on the stress categories in the ASME code section III

The structural optimization technique is well known as one of the tools to make a better design. Recently, it is applied to the design of nuclear components for the purpose of the design evolution and enhancement. When it is applied to the nuclear components, there are a couple of points to be considered. The ASME section III, design by analysis, provides stress criteria for nuclear components, which is quite different from the general stress constraints for a typical optimization process. Based on the ASME section III, stresses are categorized into three types with different stress limits. The stress limits change according to corresponding service levels. Since the types of stresses and the service levels introduce different stress, the multiple loading conditions should be utilized during an optimization. And the general stress constraints during an optimization are the maximum nodal stresses applied to the concerned points rather than the concerned section. On the contrary, the failure condition of the ASME section III can be evaluated by comparing the stress intensity, which was created by the stress linearization procedure at the concerned section, with the prescribed one. So, the linearized stresses such as stress intensities are used as stress constraints during an optimization for nuclear components. To validate the ideas, the shape of torus seal is optimized under the multiple loading conditions with the linearized stress constraints.

► A way of an optimization based on ASME code section III stress criteria is proposed.
► In optimization of a nuclear-related structure, multiple loading conditions should be utilized.
► Linearized stresses should be used as the stress constraints.
► The stress criteria of the ASME code section III was summarized per each service limit.
► One sample structure is optimized and the result is discussed.