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

The critical neutron heating in the reflector control drums is investigated for a fast incore thermionic space craft reactor for power and nuclear pro pulsion. The reactor is fueled with uranium carbide (UC) and controlled wit h the help of rotating B4C drums imbedded into the beryllium reflector. Whi le the neutron heating in the drums would not require a cooling mechanism i n the power phase, the heat generation during the thrust phase obliges cool ing for a nuclear thermal thrust around F = 5000 N by a specific impulse of 670 s(-1) at an hydrogen exit temperature around 1900 degrees K. With a be ryllium reflector without extra cooling measures, thermal thrust must be ke pt F < 2500 N to relieve the thermal load in the reflector. On the other ha nd, a reflector made of BeO may withstand a thermal load for a nuclear ther mal thrust of F = 5000 N. The neutronic analysis has been conducted in S-16 -P-3 and S-8-P-3 approximation with the help of one- and two-dimensional ne utron transport codes ANISN and DORT, respectively. A reactor control with boronated reflector drums (drum diameter = 14 cm) at the outer periphery of the radial reflector of 16 cm thickness would make possible reactivity cha nges of Delta k(eff) = 13.55%-amply sufficient for a fast reactor-without a significant distortion of the fission power profile during all phases of t he space mission. Calculations are conducted for a reactor with a core radi us of 22 cm and core height of 35 cm leading to power levels around 50 kW(e l). (C) 1998 Elsevier Science Ltd. All rights reserved.