Research on multi-objective optimization method for flow distribution of natural circulation reactor during its life-cycle

Abstract

A reasonable flow distribution can flatten the temperature distribution at the core outlet and reduce the temperature fluctuation, improving the economy and safety of the reactor. Different from a forced circulation reactor, the flow distribution of a natural circulation reactor is automatically adjusted according to the relationship between the fuel assembly power and inlet resistance. In this work, first, a local optimal flow distribution calculation model is constructed based on the closed parallel multi-channel model. Second, a Multi-objective comprehensive evaluation based on the optimal time zone is proposed to find an optimal flow distribution scheme that satisfies multiple requirements during the entire life-cycle. Third, the flow distribution scheme of a small lead-bismuth fast reactor with long life and natural circulation (SPALLER-100) is studied. The Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) algorithm is chosen as the evaluation method with three evaluating indicators for calculation. Ultimately, the subchannel code is selected to verify the flow distribution scheme. The analysis results show that the scheme based on the power distribution of 3182 days performs the best. Compared with the scheme designed by the beginning of life (BOL), the maximum outlet temperature difference reduced by 30 K, the standard deviation of the maximum outlet temperature difference reduced by 41%, and maximum output power increased by 2.35%. The results are in good agreement with the SUBCHANFLOW code, and the maximum relative error is less than 4.5%.