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The non-destructive testing of concrete used in nuclear facilities is critical as the concrete is exposed to various unfavourable conditions such as corrosion, radiation, extremely varying temperatures, and cyclic loadings over its lifetime. Such exposure can lead to concrete deterioration and moisture loss, thus compromising the shielding and structural integrity of the concrete [1, 2]. This concern is particularly relevant as the Koeberg nuclear power plant approaches the end of its planned operational lifespan, with Eskom seeking a 20-year extension overseen by the National Nuclear Regulator (NNR) [3].
Fast neutron transmission spectroscopy involves irradiating a sample with a well-characterized beam of neutrons and analysing the transmitted neutron spectrum to infer the elemental composition using a deconvolution technique [5]. In this study, we present an experimental and simulated validation of this technique using HDPE and graphite (C) to derive energy dependent removal cross sections for hydrogen. In parallel, Si, SiO2, and H2O were used to derive energy dependent removal cross sections for oxygen. Measurements were taken at the n-lab at UCT [6], using a collimated beam of neutrons produced by an americium-beryllium (AmBe) neutron source incident on samples of HDPE, C, Si, SiO2 and H2O. Neutron energy spectra transmitted through the samples were measured using an EJ-301 organic liquid scintillator coupled with spectrum unfolding methods, enabling determination of the energy-dependent effective removal cross section for each sample. To validate the use of simulated data where physical measurements may not be possible, these results were compared with removal cross sections obtained from simulations using FLUKA.
[1] Naus, D.J., The Management of Aging in Nuclear Power Plant Concrete Structures, Materials Issues in Nuclear Reactors, 61(7), pp. 35-40 (2009).
[2] Naus, D.J. et al., Nuclear power plant concrete structures – aging consideration, Challenges of Concrete Construction: Volume 6, Concrete for Extreme Conditions, pp. 747– 764 (2002).
[3] World Nuclear News, Review of Koeberg extension plans completed by IAEA Team (2022).
[4] Hutton, T., Buffler, A. and Alexander, M. Elemental analysis of concrete via fast neutron transmission and scattering spectrometry, EPJ Web Conf., 261, 03003 (2022).
[5] Hutton, T. and Buffler, A., Characterisation of neutron fields at the n-lab, a fast neutron facility at the University of Cape Town, Appl. Rad. Iso, 206:111196 (2024).
