Work is planned to formulate a physically-based conceptual model for the time-dependent metallurgical embrittlement and strengthening of typical alloys considered to be potential candidates in the high-temperature, gas-cooled reactor (HTGR) applications, particularly in the temperatures of 750' to 950' C. Phase I also is directed toward establishing the scope and feasibility of integrating the formulated model into a broader program contributing to the needed basis for the structural design and analysis of the relevant metallic components. The model is to be developed essentially to better quantify the internal material changes, particularly related to carburization, and relate these to the resulting mechanical deformation and fracture response of the material. The work plan calls for (1) an assessment of currently available test data and field observations to identify the macroscopic phenomena and failure modes of importance, (2) identification of and suggestions for the underlying physical processes and mechanisms, the resulting internal changes and variables to characterize the changes, (3) examination of the relevant thermodynamic and kinetic aspects of the key processes, (4) model development relating the results of (1) through (3) to the embrittlement and strength characteristics of the material, and (5) preliminary assessment and interpretation of the model with the scope determination for the subsequent phases of the R&D effort.Anticipated Results/Potential Commercial Applications as described by the awardee:A primary result of this R&D is expected to be a quantitative model describing the deformation and fracture characteristics of typical metallic materials under the anticipated HTGR conditions; the model also is expected to significantly contribute to the suitable realistic bases for developing the needed structural design code and/or evaluation methods. The benefits would be economic (through better uses of resources such as alloying materials and test programs), technological (through better understanding and implementation of the quantitative tools), and other (through better assessment of safety/reliability issues and advancement of the energy technology). Potential users include design engineers, material scientists, code committees, and technical/engineering staff responsible for operation-maintenanceevaluation of HTGR systems.
