MS - 168 - Radiation damage on materials involved in nuclear shielding

Concrete surrounding nuclear facilities is exposed to nuclear radiation such as neutrons, primary gamma rays, secondary gamma rays from neutron capture. Experiments have been made on irradiated concrete samples since the late '60s, often on concretes applied for the construction of existing power plants. The radiation effects were studied by several research groups and many studies agree in the critical quantities up to which radiation damage occurs: for integrated neutron fluxes of the order of 1019n/cm2 and for gamma radiation doses of about 1010rad the effects of irradiation are relatively small, while higher may lead to reductions of concrete compressive and tensile strength and modulus of elasticity depending on the incident radiation. Thermal coefficient of expansion, thermal conductivity and shielding properties are less affected by radiation. Radiation damage is known to be mainly caused by lattice defects in the aggregates, responsible of their volume increase leading to fracture; also there is evidence of an enhanced, radiation-induced degradation of concrete by alkalisilica reaction in irradiated concrete. The mini-symposium will attempt to better understand, either following a numerical approach or on experimental bases, the main problems connected to concrete shielding for nuclear research facilities or ordinary nuclear power plants, in order to clarify the effects of nuclear radiation on concrete and hopefully suggest methods to prescribe its durability in time, under this kind of severe condition.