Transformation kinetics of alloys under non-isothermal conditions

The overall solid-to-solid phase transformation kinetics under non-isothermal conditions has been modeled by means of a differential equation method. The method requires provisions for expressions of the fraction of the transformed phase in equilibrium condition and the relaxation time for transition as functions of temperature. The thermal history is an input to the model. We have used the method to calculate the time/temperature variation of the volume fraction of the favored phase in the alpha-to-beta transition in a zirconium alloy under heating and cooling, in agreement with experimental results. We also present a formulation that accounts for both additive and non-additive phase transformation processes. Moreover, a method based on the concept of path integral, which considers all the possible paths in thermal histories to reach the final state, is suggested.Comment: 16 pages, 7 figures. To appear in Modelling Simul. Mater. Sci. En

Fuel Modelling in Accident Conditions (FUMAC)

Improved understanding of fuel performance can lead to a reduction in operating margins, increased flexibility in fuel management and improved operating economics. To better understand fuel performance, the IAEA has addressed different aspects of fuel behaviour modelling in a series of coordinated research projects aimed at assessing fuel performance codes and supporting countries with code development and application needs (FUMEX series); building a database of well defined experiments suitable for code validation, in association with the OECD Nuclear Energy Agency (OECD/NEA); transferring a mature fuel modelling code to developing countries and supporting its adaptation to the requirements of particular reactors; providing guidance on applying that code to reactor operation and safety assessments; and providing guidelines for code quality assurance, code licensing and code application to fuel licensing. The present publication describes the results of the coordinated research project on Fuel Modelling in Accident Conditions (FUMAC), initiated under the IAEA Action Plan on Nuclear Safety implemented after the accident at the Fukushima Daiichi nuclear power plant. The project, which ran from 2014 to 2018, followed previous projects on fuel modelling: D-COM 1982-1984, FUMEX 1993–1996, FUMEX-II 2002-2006 and FUMEX-III 2008-2012. The project participants used data derived from accident simulation experiments, in particular data designed to investigate the fuel behaviour during design basis accident and design extension conditions, to carry out calculations on selected priority cases identified at the first research coordination meeting. These priority cases were designed to support the participants’ individual priorities and were chosen as the best available to help determine which of the many models used in the codes most closely reflect reality. The cases were also used for verification and validation purposes, and for inter-code comparisons