Year
2010
File Attachment
Abstract
A mineral filled vinylester composite used in radioactive materials transport/storage casks as a neutron shielding has been studied. The matrix is a highly hydrogenated novolac-type vinylester resin and two mineral fillers are zinc borate and aluminium tri hydrate. During the use of casks, neutrons are slowed down by hydrogen atoms contained in both resin and fillers, and then absorbed mainly by boron atoms contained in zinc borate. Aluminium tri hydrate is used for the material fire resistance and self-extinction properties. During the service life of the transport/storage casks, the neutron shielding material is subjected to three types of ageing: thermal degradation, irradiation and hydrolysis. In this paper, only thermal ageing results are discussed. The composite was cast under room temperature, cured at 80°C for 12 hours, and then post-cured at 160°C for 4 hours before ageing experiments. Gravimetric analysis data were used to evaluate weight loss of the composite after exposure to various temperatures ranging from 120°C to 160°C, under atmospheric pressure and 2×105 Pa of oxygen pressure. During the first hours of ageing, a fast weight loss was observed due to volatility of low molecular weight compounds. Then, over ageing time, the rate of weight loss decreased. Fourier transform infrared (FTIR) spectroscopy measurements were carried out in transmission mode to investigate C-H aliphatic bonds consumption and carbonyl functions build up. In addition, glass temperature (Tg) was monitored using dynamic mechanical thermal analysis (DMTA). To investigate the effect of thermal ageing on the composite mechanical properties, flexural modulus and ultimate stress were determined prior and after exposure. Key words: ageing, neutron shielding, vinylester, mineral fillers, gravimetric analysis, FTIR, DMTA, flexural modulus and ultimate stress.