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Reactor fuel's power distribution plays a vital role in designing the new generation thermionic Space Reactor Power Systems (SRPS). In this paper, the 1/12th SPACE-R's full reactor core was numerically analyzed with two kinds of different axial power distribution, to identify their impacts on thermal-hydraulic and thermoelectric characteristics. In the benchmark study, the maximum error between numerical results and existing data or design values ranged from 0.2 to 2.2%. Four main conclusions were obtained in the numerical analysis: a) The axial power distribution has less impact on coolant temperature. b) Axial power distribution influenced the emitter temperature distribution a lot, when the core power was cosine distributed, the maximum temperature of the emitter was 194 K higher than that of the uniform power distribution. c) Comparing to the cosine axial power distribution, the uniform axial power distribution would make the maximum temperature in each component of the reactor core much lower, reducing the requirements for core fuel material. d) Voltage and current distribution were similar to the axial electrode temperature distribution, and the axial power distribution has little effect on the output power.

An appropriate method for selecting the axial power distribution that results in the most conservative thermal margins was developed in this study. Nuclear physics calculations provided axial power distributions with various shapes based on the core states and cycles. A total of 17 cycles were required to reach the equilibrium core from the initial core. The axial power distributions were sorted based on the power peaking and sum-to-peak (STP) values. In the present study, three different power peaking criteria were used to sort the axial power distributions: the upper 50%, upper 25%, and upper 10%. After the first sorting based on the power peaking, the axial power distributions were grouped based on the power peak location in the axial direction. In each group, the axial power distribution with the highest STP was chosen for thermal margin analyses. In addition, the axial power distributions in the hottest channel and fuel assembly from the initial to the equilibrium core were obtained. Since the axial power distributions in the hottest channel and fuel assembly were bounded by the axial power distribution with the upper 10% F Q , the thermal hydraulic analysis results gave the more conservative thermal margins using the selection method presented in this study. The Onset of Nucleate Boiling (ONB) temperature margin with the upper 10% F Q was 22.5 °C, but it was 25.0 °C for the hottest channel. Therefore, the axial power distribution used for thermal hydraulic and safety analyses should be selected using the appropriate method presented in this study. [ABSTRACT FROM AUTHOR]

• An axial power distributed control system for fast nuclear reactors is presented. • The discretization process of the PSD controller is presented. • The effectiveness of PSD method is verified in the semi-physical test platform. • The PSD method provides simpler design and better dynamic performance than LPC. Axial power distribution control is one of the key issues for Nuclear Power Plant (NPP) operation. In the most of NPPs, the axial power distribution control is realized by the Lumped Parameters Control (LPC) method, which often takes the axial power difference between adjacent nodes as the controlled object. However, the nuclear reactor core has a typical distributed parameters feature. With the number of discrete nodes increases, the control system design is more and more complex. Therefore, it is necessary to develop the Distributed Parameter Control (DPC) method. In this work, a DPC method based on the Proportional Spatial-Derivative (PSD) controller is presented. Experiments show that the power distribution control system based on the PSD control method can inhibit the power peak. Meanwhile, the comparison between the PSD and PID controllers shows that the DPC system based on the PSD method has better dynamic performance than LPC system. [ABSTRACT FROM AUTHOR]