Nuclear Science User Facilities 64 The long-term stability and performance of Portland cement concrete in nuclear power plants is of concern as little opera- tional or experimental data exist to aid regulators in extending operating licenses. More complete knowledge of performance in radiation environ- ments will determine concrete’s role in setting the upper limits for lifetime extensions. In the awarded project, concrete, aggregate, and paste samples were irradiated with energetic protons to simulate radiation damage. Volatile loss during irradiation was monitored with a mass spectrometer to determine the ideal conditions to irradiate the concrete and concrete components. Samples were examined with optical and electron microsope post irradia- tion to determine the degree of surface damage. Collected results were used to determine possible radiation induced degradation in the current fleet, as well as aid in developing radiation tolerant concrete recipes for future plants and storage containers. The experiments further establish considerations for accelerated irradiation studies of concrete, which may be required due to the hydrous nature of the material. Project Description The technical objectives of the research are to understand the radiation tolerance of concrete and how to perform more-detailed accelerated- irradiation experiments in the future. Most accelerated-aging experiments using accelerators require the target materials to be stable in a vacuum environment; this is true for nearly all metal and ceramic materials. However, due to the hydrous nature of concrete, it requires extensive pump-down times prior to performing any irradiations. The hydrous nature further complicates experiments because using the most modest of beam fluxes can result in vacuum pressure changes two orders of magnitude and greater. Changes Irradiation Effects on Structure and Properties of LWR Concrete Chris Wetteland – University of Tennessee – Figure 1. Optical microscope image at 50, 100, and 150× magnification shows discoloration and cracking in the nanoconcrete surface. This flux used in this irradiation was 5 × 1013 protons/cm2 and resulted in significant volatilization from the surface. Accelerated aging experiments in concrete may offer insight into the longevity of this crucial reactor building material.