The use of plastics and elastomers in nuclear radiation

Abstract

Common plastics and elastomers are described in general with emphasis on the relation between chemical structure and engineering properties and applications. The interaction of radiation with organic materials is presented very briefly and radiation-induced crosslinking and scission, which lead to changes in physical properties, are discussed. The radiation-induced changes in specific plastics are described. Polyethylene, which can be regarded as a prototype for the more complex polymers, develops crosslinks at the rate of 1 to 1.5 for every 100 eV of radiation energy absorbed. The hardness and elastic modulus increase and the flexibility and ductility decrease until the usefulness at doses above 10 9 rads is uncertain for some applications. Polystyrene demonstrates stabilization by the aromatic ring, undergoing change at a lower rate than polyethylene. Polymethyl methacrylate exemplifies polymers containing the quaternary carbon atom, which leads to chain scission and rapid loss of strength properties. Polymers with a high content of strongly electronegative elements also degrade rapidly. Elastomers are discussed separately because elasticity and flexibility are affected very rapidly by the crosslinking and scission produced by radiation. Finally, various applications of plastics and elastomers in reactor systems or their vicinity are discussed. The properties which are important to the application are presented along with the radiation-induced changes in these properties.