Design and criticality analysis of colloidal slurry nuclear reactors Diego Laramore, Michael P. Pfeifer, Jordan Lindstrom, Hitesh Bindra ⇑ Department of Mechanical and Nuclear Engineering, Kansas State University, Manhattan, KS 66506, United States article info Article history: Received 23 June 2017 Received in revised form 28 August 2017 Accepted 1 September 2017 Keywords: Colloidal slurry Critical reactor MCNP model abstract A novel nuclear reactor concept is presented in this paper which can sustain the controlled fission reac- tion and has an innovative mechanism of reactivity control. The concept of this reactor is based on the stability of colloidal suspensions. These suspensions consist of colloidal fuel particles suspended in a moderator with a controllable separation distance. The packing factor of the colloidal suspension can be controlled by slightly modifying the ionic concentration of the suspension medium, effectively con- trolling the criticality of the reactor. Based on local average separation distance between particles, ther- malization of neutrons can be varied and can be used to manipulate neutron multiplication factor k 1 . Numerical calculations are performed with the help of MCNP software to obtain optimal configuration of critical assemblies. For the numerical case studies presented in this paper, uranium dioxide ðUO 2 Þ fuel particles with size P10 lm in different liquid solvents are considered. The fuel particles are simulated as hard spheres packed in Bravais lattice structures within the solvent medium. Simulations involve neutron interactions of a uniform colloidal suspension of spherical fuel elements of diameters 5 cm–0.001 cm. The homogeneous fuel equivalence was found to occur for particles sized below 0.010 cm diameter. Criticality curves are generated for fuel particle configurations with varying particle density, confirming fuel config- urations can be controlled by only modifying particle packing factor. Additional criticality curves are gen- erated for various cylindrical geometries of fuel suspension vessels with modular form factors. Triethylene glycol is substituted as a moderator and suspension fluid with higher boiling point as com- pared to water. The type of moderator or solvent does not have any significant impact on criticality performance. Ó 2017 Elsevier Ltd. All rights reserved. 1. Introduction Nearly all nuclear power reactors currently operating around the world are heterogeneous thermal reactors i.e. the reactor core consists of lumped regions of fuel surrounded by moderator. There are several advantages of heterogeneous assembly of fuel- moderator over homogeneous mixture, but one of the most signif- icant advantage is the improvement in multiplication factor by increasing the resonance escape probability of neutrons emitted after fission reaction (Lamarsh, 1966). The critical condition of the reactor must be controlled by some means other than changing the properties of the fuel or the geometry of the reactor, normally by introducing neutron absorbing control rods into the core. The dependence on neutron absorption as the principal control scheme reduces the actual burnup of the fuel. The inclusion of mechanical control elements increases the minimum size of the reactor and also requires excess reactivity. Similarly, the heat transfer process becomes complex as reactor coolant is circulated other indirect heat exchange loops. Therefore some of desirable features of a homogeneous reactor such as simplified control system and heat transfer system (Lane, 1958; Bajorek et al., 2010) are no longer available in these heterogeneous reactors. In this paper a novel reactor concept consisting of a colloidal slurry of fuel particles in a neutron moderating solvent is pre- sented and analyzed. Such a reactor would be able to adjust the pitch distance between its fuel elements (fuel particles) during operation, eliminating the need for an absorbing control medium. The effective neutron multiplication factor (k eff ) of the colloidal suspension can instead be adjusted by influencing the electro- static and van der Waal forces present between suspended fuel particles in a colloidal suspension. A conventional example of this physics is seen in day to day life if one adds vinegar into milk resulting into cottage cheese suspension. Apart from innovative control mechanism, this design offers to retain the advantages of both heterogeneous and homogeneous reactors. The goal of this paper is not to present any merits of this new conceptual reactor design but to present this idea and relevant criticality calculations in a generalized manner. http://dx.doi.org/10.1016/j.anucene.2017.09.005 0306-4549/Ó 2017 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: hbindra@ksu.edu (H. Bindra). Annals of Nuclear Energy 111 (2018) 255–261 Contents lists available at ScienceDirect Annals of Nuclear Energy journal homepage: www.elsevier.com/locate/anucene