b'Accomplishments: Engineers from INLs irradiation experiment design and supporting groups developed three major systems in 2018 with pertinence to microstructural-focused experimenta-tion in TREAT. All of these systems make use of the MARCH system for its modular mechanical layout. The first development was a heater module which can be installed in the MARCH pressure pipe to enable electrical heat up to 700C prior to irradiation, or to create longer duration temperature-controlled histories during irradiation. The heater module mounts on an upper ring which enables smaller test modules to pass through. One heater module was constructed and used successfully in the irradiation discussed below. A second heater module is under fabrication with optimized thermocouple placement to enable full temperature operations.The second major development was supported by the I2 program for an in-pile demonstration of a novel sensor applying resonant ultrasonic spectroscopylaser (RUSL) to infer changes in material microstructure. This method uses laser ultrasonics for measuring changes in the elastic stiffness tensor caused by grain restructuring (recrystallization). In this arrangement a fiber delivers an amplitude modulated laser to the base of the cantilever beam which excites Figure 1. Design rendering of the RUSL irradiation device.2019|AFC ACCOMPLISHMENTS 205'