Critical neutron heating in the control drums of a dual purpose thermionic space reactor for power and propulsion

摘要

The critical neutron heating in the reflector control drums is investigated for a fast incore thermionic space craft reactor for power and nuclear propulsion. The reactor is fueled with uranium carbide (UC) and controlled with the help of rotating B_4C drums imbedded into the beryllium reflector. While the neutron heating in the drums would not require a cooling mechanism in the power phase, the heat generation during the thrust phase obliges cooling for a nuclear thermal thrust around F= 5000 N by a specific impulse of 670 s~-1 at an hydrogen exit temperature around l900"K. With a beryllium reflector without extra cooling measures, thermal thrust must be kept F< 2500 N to relieve the thermal load in the reflector. On the other hand, a reflector made of BeO may withstand a thermal load for a nuclear thermal thrust of F= 5000 N. The neutronic analysis has been conducted in S~I6-P_3 and S_8-P_3 approx- imation with the help of one- and two-dimensional neutron transport codes ANISN and DORT, respectively. A reactor control with boronated reflector drums (drum diame- ter = l4cm) at the outer periphery of the radial reflector of l6cm thickness would make pos- sible reactivity changes of K_eff = l3'55/100--amply sufficient for a fast reactor--without a significant distortion of the fission power profile during all phases of the space mission. Cal- culations are conducted for a reactor with a core radius of 22cm and core height of 35cm leading to power levels around 50 KW.l'