Startup and control of out-of-core thermionic space reactors

An analysis of out-of-core thermionic space reactor (OTR) startup and control has been performed. The reference ionic thermal reactor (ITR) chosen for this study is a 75 kWt version of the STAR-C (GA Technologies 1987). The applicability of point kinetics was first verified for the reference OTR system. Point kinetics applicability was verified for core length-to-diameter (L/D) ratios of two and four, and for both subcritical-to-critical and critical-to-supercritical transients. A coupled thermal/point kinetics code was then written, and OTR startup was analyzed. The analyses lead to several observations. First, point kinetics is applicable to the reference OTR for all transients considered. Second, to achieve a 900 second startup the reference OTR must operate at powers well above steady-state rated power during startup. Finally, the large thermal inertia of the radial reflector could be used to reduce radiator temperature during the first several hundred seconds of operation. Further research should be performed on transient heat pipe operation and on off-normal thermionic converter operation.