Temperature feedback effect to stationary wave of nuclear fusion

Nuclear fission wave (NFW) of steady shape in the travelling wave reactor (TWR) was investigated. In this work burnup equations together with one-dimensional diffusion equation in the one-velocity approximation, taking into account temperature feedback in the simplest form was solved. Velocity characteristics of TWR, which is dependence of velocity on the effective absorber density for the stationary wave solutions were analytically introduced and described. Both analytical and numerical results indicate that the velocity characteristics in case of the U-Pu cycle are double-valued, with the solutions of the lower branch, being unstable. This implies that the minimum possible velocity of the stationary wave exists. It was shown that the velocity characteristics of TWR are formed by the three distinct mechanisms related to: feedback to power, and kinetics of unstable nuclides 239Np and 241Pu. Effects of the intermediate nuclide 239Np kinetics and of the feedback to power are additive and compete to that of 241Pu kinetics, with the result depending on the velocity of the wave. At typical parameters of TWR all three mechanisms contribute significantly to the velocity characteristics. Strong negative feedback to power makes the region of the absorber concentration, where the NFW may exist smaller, and slows down the NFW