TOPAZ-Ⅱ反应堆堆芯的稳态热工代理模型

The TOPAZ-Ⅱ reactor, a space nuclear reactor power designed by the former Soviet Union, uses sodium-potassium alloy (NaK-78) as coolant and adopts thermionic conversion power generation principle to provide power for the load. To quickly and accurately calculate the steady state thermal parameters of the core, a steady state high-precision thermal surrogate model of the core was established. This study firstly used Fluent to carry out thermal calculation of core steady state, with grid node temperatures along the central longitudinal cross-section selected as sample data. Then the main features in samples were extracted by Proper Orthogonal Decomposition (POD) method, and the top 10 modes were retained based on 99.999% energy proportion for model order reduction. Finally, through Back Propagation (BP) neural network, the steady state thermal surrogate model of core was established and was compared and validated with Fluent. The results show that the maximum error of the surrogate model in calculating the temperature at grid nodes is 9.95 K, the relative error is less than 1% and the calculation time is less than 1 s. Taking the outlet temperature of the hottest coolant channel as a reference, the flow-power percentage ratio of the coolant to maintain the single-phase working state should be greater than 0.35 calculated by the thermal surrogate model. Therefore, the thermal surrogate model established in this paper can quickly and accurately calculate the steady state thermal parameters of the core, achieve simulation prediction of the core, and provide certain reference for the thermal safety analysis of the core.