Reactor operating on a slow wave of nuclear fission

Abstract

A simplified system of equations is used to investigate the properties of autowaves of slow nuclear burn, which under certain circumstances can propagate in a medium containing 238 U (or 232 Th). It is shown that the reactor spectrum and the presence of other substances in the medium which determine the critical concentration of plutonium (or 233 U) affect the appearance of a wave.The innovative designs of nuclear reactors that the world community has been scrutinizing in the last few years are oriented toward increasing safety and improving the fuel cycle -the possibility of burning transuranium elements and using the enormous stores of 238 U and 232 Th. We believe that a reactor based on the appearance of a slow wave of nuclear combustion in a medium consisting of pure 238 U solves both problems -nuclear safety and 238 U utilization, but only if it can be built. It is shown in [1] that a neutron-fission wave can propagate in a 238 U medium under certain conditions. Indeed, if the half-space filled with a substance containing uranium is irradiated with neutrons, plutonium will accumulate near the surface. In time, the plutonium concentration can reach a critical level and then the system can be capable of self-multiplication. The neutrons flying out of the reaction zone are trapped by the next layers of uranium. Plutonium also accumulates in these layers. Under certain conditions, the active zone moves and the plutonium accumulates in subsequent layers. As a result, there arises a stationary wave on whose front uranium is reprocessed into plutonium as a result of neutron fission.It was stated in [2, 3] that the realization of such a regime in a reactor will make the reactor inherently safe. A concept of a fast reactor operating in a self-regulated regime 100 m underground for 30 yr without any direct participation by humans is presented in [4]. The operation of such a reactor is safe. New models oriented toward the development of an advanced fast reactor are proposed in [5,6]. It is shown by means of mathematical simulation that the period of a reactor operating in the self-regulated regime reaches 11 days, while the period for ordinary reactors is several minutes (the period of a rector is the time over which the power increases by a factor of e). A model of a reactor burning metallic fuel is proposed in [3], and it is shown that in the absence of control the power of the reactor changes by 2.5% over 2 yr. Even though the authors of [3, 5, 6] refer to [1] an autowave of plutonium fission does not form in their works and the reactors studied which they study are not stationary, since without regulation their power changes in time. This could be due to geometric effects or the choice of the initial condition. At the same time, the autowave regime is the most interesting one. For this reason, the conditions under which it arises should be analyzed first on the basis of simplified equations and then using more realistic mathematical models.

Design and performance of 2D and 3D-shuffled breed-and-burn cores

“…Since 2006, when Bill Gates announced support and funding for the idea (TerraPower, 2015), a large number of groups have started research on the topic. Some of the more recently published researched is presented in references (Pavlovich et al, 2007;Rusov, 2011;Hartanto and Kim, 2012;Osbourne et al, 2012;Choi et al, 2013;Si, 2013;Heidet and Greenspan, 2013a,b).…”

Traveling Wave Reactor and Condition of Existence of Nuclear Burning Soliton-Like Wave in Neutron-Multiplying Media

“…This leads, in fact, to transformation of fast wave into slow wave or to its full stop. It is interesting to note that this case is not discussed in the literature (with the exception of [8,10]), but it is possible to assume that it corresponds to some hypothetical situation, when the nuclear burning wave forms in highly enriched fuel which has the ultra-low critical concentration of fuel fissionable component.…”

Newton’s second law analogy for the traveling wave of nuclear burning

“…Its autowave form is also obtained. In contrast to many other papers like [1,3,5,11,16,17], in which it was also considered in autowave form, we do not neglect the derivative of neutron concentration with respect to time in the neutron diffusion equation. This way we study the non-stationary traveling-wave burning mode.…”

“…Let us note that equation (26) looks like this because we did not neglect the derivative over time in the system of kinetic equations, when switching to the autowave variable z = y + ut in Section 2, as it was done e.g. in [1,3,5,11,16,17].…”