Thermal neutron scattering kernels for uranium mono-nitride: A potential advanced tolerant fuel candidate for light water reactors Iyad Al-Qasir a,b,⇑ , Victor Gillette a,b , Abdallah Qteish c a Department of Mechanical and Nuclear Engineering, University of Sharjah, Sharjah, United Arab Emirates b Center for Advanced Materials Research, Research Institute of Sciences and Engineering, University of Sharjah, Sharjah, United Arab Emirates c Physics Department, Yarmouk University, Irbid, Jordan article info Article history: Received 18 July 2018 Received in revised form 5 November 2018 Accepted 27 November 2018 Keywords: Uranium mono-nitride Thermal neutrons Scattering cross sections Phonons First-principles calculations Light water reactors Advanced tolerant fuel ENDF/B-VIII abstract The use of uranium mono-nitride (UN) fuel in light water reactors has recently received an increasing interest. Neutronic and thermal-hydraulic performance of UN and associated composite fuels have been studied lately for several types of light water reactors. A comprehensive and detailed analysis of the per- formance of these reactors using nitride fuels require a complete set of thermal neutron scattering libraries of UN. In this work, the thermal neutron scattering law, the inelastic and coherent elastic scat- tering cross sections of UN are calculated at different temperatures starting from the phonon density of states obtained from first-principles electronic structure calculations. Excellent agreement between the calculated phonon dispersion relations and the experimental data have been obtained. Due to the huge mass difference between the constituent elements, the calculated nitrogen optic phonon modes are well- separated from those of uranium acoustic phonon modes. The nitrogen scattering law shows a set of well-defined and equally-spaced peaks corresponding to multi-phonon scattering processes, demonstrat- ing that the nitrogen atoms behave as nearly independent three-dimensional quantum harmonic oscilla- tors. The effects of this behavior on the computed inelastic scattering cross sections are thoroughly discussed. As 14 N has a large absorption cross section in the thermal energy range and results in a pro- duction of 14 C, the scattering law and the inelastic scattering cross section of U 15 N are also calculated. Our calculated scattering cross sections are discussed in comparison with the ENDF/B-VIII.0 thermal neu- tron scattering cross sections of UN and UO 2 , and it has been found that U 15 N fuel can be a viable alter- native to the UO 2 one. Ó 2018 Elsevier Ltd. All rights reserved. 1. Introduction Since the Fukushima-Daiichi nuclear power plant complex event in 2011, developing fuels and claddings with accident toler- ant characteristics for use in commercial light water reactors becomes a central goal (Kurata, 2016; Spencer et al., 2016). There- fore, there has been a growing interest in using ceramic fuels other than UO 2 in the next generation light water reactors. Neutronic and thermal-hydraulic performance of UN and associated composite fuels have been studied lately for several types of light water reac- tors (LWRs), such as, the boiling water reactor (BWR) (Zakova and Wallenius, 2012), the pressurized water reactor (PWR) (Xu et al., 2012; Brown et al., 2014; Saadi and Bashiri, 2016; Spencer et al., 2016) and the super critical water reactor (SCWR) (Chaudri et al., 2013). The latter is the only concept of Generation IV nuclear reac- tors cooled and moderated by light water. These studies have shown that replacing the conventional UO 2 fuel by UN fuel has two main advantages: (i) Increases the fuel cycle length (Zakova and Wallenius, 2012; Saadi and Bashiri, 2016) which means a lower electricity cost. This is because UN has higher uranium den- sity than UO2. (ii) Reducing significantly the axial fuel centerline temperature (Chaudri et al., 2013; Saadi and Bashiri, 2016), which will provide a larger safety margin from the fuel melting point and lead to a considerable future enhancement of LWR thermal power. This advantage is mainly due to the high thermal conductivity of UN which increases with increasing temperature and reaches a value that is many times higher than that of UO 2 at 1000 K. It is worth mentioning that UN has a melting point that is comparable to that of UO 2 (Simnad, 2003). Moreover, nitride fuels are well- suited with the Plutonium Uranium Redox Extraction (PUREX) method (Raj et al., 2015). https://doi.org/10.1016/j.anucene.2018.11.047 0306-4549/Ó 2018 Elsevier Ltd. All rights reserved. ⇑ Corresponding author at: Department of Mechanical and Nuclear Engineering, University of Sharjah, P.O. Box: 27272, Sharjah, United Arab Emirates. E-mail address: alqasir@sharjah.ac.ae (I. Al-Qasir). Annals of Nuclear Energy 127 (2019) 68–78 Contents lists available at ScienceDirect Annals of Nuclear Energy journal homepage: www.elsevier.com/locate/anucene