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CIVIL AND STRUCTURAL ENGINEERING COMPUTATIONAL TECHNOLOGY
Edited by: B.H.V. Topping and Y. Tsompanakis
Concrete as the Multiphase Material in Biological Shields against Nuclear Radiation
C.E. Majorana1, B. Pomaro1, V.A. Salomoni1, F. Gramegna2 and G. Prete2
1Department of Structural and Transportation Engineering, University of Padua, Italy
C.E. Majorana, B. Pomaro, V.A. Salomoni, F. Gramegna, G. Prete, "Concrete as the Multiphase Material in Biological Shields against Nuclear Radiation", in B.H.V. Topping and Y. Tsompanakis, (Editor), "Civil and Structural Engineering Computational Technology", Saxe-Coburg Publications, Stirlingshire, UK, Chapter 2, pp 35-64, 2011. doi:10.4203/csets.28.2
Keywords: shielding, radioactive ion beams, radiation damage, nuclear facility, concrete durability, radiation heat, coupled problem.
Nuclear radiation is known to affect the mechanical behavior of concrete above specific threshold quantities of radiation fluence, namely neutron fluences of the order of 1019 n/cm2 are known to be critical for its compression and tension strength and Young's modulus.
The present work seeks to model damage from nuclear radiation for concrete structures exposed to high energy neutron flux, which represent the next generation facilities designed for the production of high energy radioactive ion beams (RIB) in physics research. Particularly, the case study is represented by a research nuclear facility of next design by the National Institute of Nuclear Physics (INFN) at Legnaro, Padua, namely: the SPES Project.
With this purpose, a damage law responsible for the strength decay of the material under severe neutronic exposure, and experimentally based, has been defined and introduced as an upgrade of the finite element research code assessing the coupled thermo-hygro-mechanical behaviour of concrete, modelled as a multi-phase porous medium, named NEWCON3D. The required damage law is thought to be a function of the neutron flux impinging the concrete shielding wall and, with respect to this quantity, it describes the decay of the Young's modulus of the material, in accordance with the effective stress theory.
Radiation damage is supposed to interact with other forms of damage, already present in the code: mechanical damage due to external loads and thermo-chemical damage arising from the high temperature behaviour of concrete, in order to assess the durability of the shielding facility, subject to a severe neutron production.
The physical quantities are investigated with Monte Carlo simulations using Fluka, a code developed by CERN and INFN of Milan; Fluka results have been properly interfaced with NEWCON3D in order to investigate the trend of humidity, temperature and mechanical quantities for the directly impinged portion of the concrete shield and, possibly, identify limits to the working of SPES, which guarantee admissible temperature gradients for concrete, under service conditions.
Temperature effects arising from radiation heat, produced in the shield as a consequence of the absorption of radiation, are shown to be more strict than the damage due to the expected neutron fluence and 4500 hours per year, i.e. approximately six months, are shown to be the admissible time span of the continuous work of the facility.
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