The American Society of Mechanical Engineers Boiler and Pressure Vessel Code, Section III “Rules for Construction of Nuclear Facility Components”, Division 5 “High Temperature Reactors”, Subsection HH “Class SN Nonmetallic Core Components”, Subpart A “Graphite Materials”, has a list of materials properties that must be measured and included in the materials data sheet (MDS) for each grade of graphite to be used in a reactor core. Two sections of the MDS includes measuring the effects of degradation, due to oxidation or neutron irradiation damage, on these materials properties. A program at Oak Ridge National Laboratory (ORNL), supported by X Energy, LLC., began in 2017 to produce the irradiation-induced property change results of graphite grades that will be used in the X Energy Xe-100 small modular reactor. Significant effort has been performed around the world to capture these property changes for a range of graphite grades through both the US Advanced Graphite Creep program, and the EU INNOGRAPH/ARCHER program. But both programs were primarily targeted towards higher temperature reactor designs that were of greater importance at the beginning of both programs resulting in a lack of data for temperatures below 600°C. The program at ORNL has been developed to produce the data necessary to assist with completing the irradiation effects on materials properties of the MDS for the graphite grades of interest for X Energy. This paper will discuss the design of the irradiation program including the irradiation conditions (neutron fluence and irradiation temperatures), the types of specimens being used in this program, and the irradiation methodology.

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