Composition optimization strategy based on multiple radiological responses for materials in spatially and temporally varying neutron fields

Abstract

Structural materials present in and around any fusion device will face stringent conditions due to the high-energy and high-flux neutrons emitted from the fusion plasma. These neutrons can cause induced radioactivity, gas production, energetic knock out atoms, atomic displacement and decay heat in these materials. This would have a significant life-limiting impact on the materials and would also cause biological hazards and radioactive waste. Hence designing low activation materials for fusion devices is warranted. This paper presents a novel tool for quantification of radiological responses in terms of the elements present in the initial material composition. Such a framework would help in the identification and optimization of the fraction of most dangerous elements/isotopes from the material composition. In practical scenarios, the material encounters a large spatial and temporal variation of neutron fluxes. This problem has been effectively treated in the present work using a multi-parameter optimization scheme. The scheme optimizes the material composition (elemental or isotopic) based on various nuclear responses and there spatial and temporal variations within the user-defined constraints. This scheme is further included in the multi-point activation code ACTYS-1-GO. The tool provides a comprehensive picture of the material response during neutron irradiation and after shutdown, enabling the assessment of structural integrity of components in a fusion device. As an aide to the material optimization process, this paper also introduces a visual representation of the evaluated information like quantification of radiological responses produced by the parent elements/isotopes in a material. This has been implemented through a series of spectrum independent and spectrum-dependent diagrams called the radiation response diagrams. These diagrams show the variation of contributing parents toward the radiological responses as a function of cooling time. Such a graph could be very useful as a first approximation for material design.