aggregates can swell and make the shield mechanically unsound. Numerous studies have shown decreases in both compressive and tensile strength as well as elastic modulus of concrete at around a dosage of around 1019 neutrons per square centimeter. These trends were also shown to exist in reinforced concrete, a composite of both concrete and steel. The knowledge gained from current analyses of materials in fission reactors in regards to the effects of temperature, irradiation dosage, materials compositions, and surface treatments will be helpful in the design of future fission reactors as well as the development of fusion reactors. Solids subject to radiation are constantly being bombarded with high energy particles. The interaction between particles, and atoms in the lattice of the reactor materials causes displacement in the atoms. Over the course of sustained bombardment, some of the atoms do not come to rest at lattice sites, which results in the creation of defects. These defects cause changes in the microstructure of the material, and ultimately result in a number of radiation effects. Radiation damage event Interaction of an energetic incident particle with a lattice atom Transfer of kinetic energy to the lattice atom, giving birth to a primary displacement atom Displacement of the atom from its lattice site Movement of the atom through the lattice, creating additional displaced atoms Production of displacement cascade (collection of point defects created by primary displacement atom) Termination of displacement atom as an interstitial Radiation cross section The probability of an interaction between two atoms is dependent on the thermal neutron cross section (measured in barn). Given a macroscopic cross section of (where is the microscopic cross section, and is the density of atoms in the target), and a reaction rate of (where is the beam flux), the probability of interaction becomes Pdx = Njσ(Ei)dx = Σdx.(what do any of these symbols mean?) Listed below are the cross sections of common atoms or alloys. Thermal Neutron Cross Sections (Barn) Microstructural evolution under irradiation Microstructural evolution is driven in the material by the accumulation of defects over a period of sustained radiation. This accumulation is limited by defect recombination, by clustering of defects, and by the annihilation of defects at sinks. Defects must thermally migrate to sinks, and in doing so often recombine, or arrive at sinks to recombine. In most cases, Drad = DvCv + DiCi >> Dtherm, that is to say, the motion of