Diffusion Theories of Nuclear Reactors

In Chap. 3 , the diffusion equation involving the behavior of neutrons in a medium was described as follows: \( \frac{1}{\upsilon}\frac{\partial \phi \left(r,t\right)}{\partial t}=D{\nabla}^2\phi \left(r,t\right)-{\Sigma}_a\phi \left(r,t\right)+s\left(r,t\right) \) In that case, the neutron source s(r, t) was given as a fixed external neutron source, such as 252Cf or 241Am ‐ Be, which was considered separately from the medium where the behavior of neutrons was considered. In addition, the system was assumed as one without fission (a non-multiplication system). In actual nuclear reactors, however, most of the neutrons come from fission. In this chapter, the system with fission (a multiplication system), which is seen in actual reactors, is considered.