Session: CS-15-01 Mechanical Properties of Nuclear Graphite and Their Implementation in Codes and Standards (Joint with MF-29) – 1

Paper Number: 105209

105209 - Semi-Empirical Modeling of Irradiation Induced Dimensional Change of Nuclear Graphites 

Nuclear graphite has been used as a moderator material in nuclear reactor designs dating back to the first reactor to reach criticality, Chicago Pile 1 in 1942. In addition, it is anticipated to be used in the conceptual Generation four (GenIV) Molten-salt reactors (MSRs), and the High-temperature gas-cooled reactors (HTRs). The macroscopic dimensional change observed in irradiated nuclear graphite is a property change of significant importance. In large part, volumetric change provides valuable insight into the in-service lifetime of graphite components used in nuclear reactors. The dimensional change behavior varies amongst each grade of nuclear graphite due to processing techniques and the resulting microstructure. In this work, a semi-empirical methodology is proposed to describe the dimensional change behavior in nuclear graphites. The turnaround point, or when there is a reversal of the dimensional change from contraction to expansion, is proposed to be a thermally activated process and thus can be described by an Arrhenius model. On the atomic scale, all nuclear graphites are the same, sp^2-bonded carbon atoms with some degree of disorder.  Towards that end, there should exist a universal activation energy common amongst all grades of nuclear graphite, and the macroscopic baseline properties unique to each grade of nuclear graphite may be described by the pre-exponential constant of the Arrhenius function. 

Presenting Author: Steve Johns Idaho National Laboratory

Presenting Author Biography: Dr. Johns was awarded his Ph.D. in Materials Science and Engineering from Boise State University in 2020. His dissertation was entitled "Defect Evolution in High-Temperature Irradiated Nuclear Graphite". Since then, he has taken a position at Idaho National Laboratory as a Materials Scientist working under the Department of Energy's (DOE) Advanced Reactor Technologies (ART) program. Specifically, his work focuses on irradiation damage mechanisms and property change in nuclear graphite. Dr. Johns also has a strong materials characterization background and is an in-situ transmission electron microscopy expert.

Authors:

Steve Johns Idaho National Laboratory
William E. Windes Idaho National Laboratory