The effect of gamma irradiation on hardening self-compacting mortar in the Belgian supercontainer concept for high level radioactive waste disposal

Author(s): H. Craeye, G. De Schutter, I. Gerardy, M. De Raemaeker, K. Gevers
Paper category: Conference
Book title: 2nd International conference on Microstructural-related Durability of Cementitious Composites
Editor(s): Guang Ye, K. Van Breugel, Wei Sun, Changwen Miao
Print ISBN: 978-2-35158-129-2
e-ISBN: 978-2-35158-123-0
Publisher: RILEM Publications SARL
Pages: 1578- 1586
Total Pages: 8
Language: English

Abstract: 
For the disposal of vitrified high level waste assemblies, which are highly active (high concentration of beta and gamma radiation resulting in heat emitted by this type of waste), the use of cylindrical concrete supercontainers is considered as the reference design in Belgium, based on the use of an integrated waste package composed of a carbon steel overpack surrounded by a massive concrete buffer based on Ordinary Portland Cement. Once the buffer is cast and hardened sufficiently in controlled environment, the radwaste is emplaced inside the buffer, the remaining gap is filled by casting a fresh mortar material (the filling) and the container is closed by fitting the lid. As a consequence, the concrete buffer, the filling and the lid, will be exposed to the effect of the heat-emitting radioactive waste during hardening (the filling) and in a hardened state (the buffer and the lid). The effect of gamma radiation (with a relevant dose rate) on the strength of the hardening filling is investigated in a preliminary study, by means of compressive strength tests, sample weighing, fluorescence microscopic test methods and scanning electron microscopy, to verify whether a possible strength loss can be noticed and to identify the main mechanisms behind the strength variations, e.g. by evaluating the possible changes in capillary porosity or to evaluate the drying process due to gamma irradiation. Furthermore, the simulations of the early-age behaviour of the concrete buffer of the supercontainer indicate a possible macro cracking risk of the outer concrete buffer, mainly devoted to the thermal expansive behaviour of the carbon steel overpack. The main goal is to prevent through-going concrete macro cracking of the buffer and the filler material, as it facilitates transport mechanisms of aggressive species once placed in the underground disposal galleries and this might jeopardize the durability of the radiological Second International Conference on Microstructural-related Durability of Cementitious Composites, 11-13 April 2012, Amsterdam, The Netherlands Second International Conference on Microstructural-related Durability of Cementitious Composites, 11-13 April 2012, Amsterdam, The Netherlands protection medium. An efficient way to overcome this cracking nature can be achieved by reducing the modulus of elasticity of the filler material, which can be a consequence of irradiation by means of gamma rays during hardening of the cementitious filling.

Online publication: 2013
Publication Type: full_text
Public price (Euros): 0.00