Neutronics Benchmark of CEFR Start-Up Tests: temperature coefficient, sodium void worth, and swap reactivity

The China Institute of Atomic Energy (CIAE) proposed some of the China Experimental Fast Reactor (CEFR) neutronics start-up test data for the IAEA benchmark within the scope of the IAEA’s coordinated research activity. The coordinated research project (CRP) on “Neutronics Benchmark of CEFR Start-Up Tests” was launched in 2018. The benchmark aims to perform validation and verification (V&V) of the physical models and the neutronics simulation codes by comparing calculation results against collected experimental data. Twenty-nine participating research organizations finished performing independent blind calculations and refined their calculation results by referring to measurement data. The paper introduces the following three kinds of reactivity measurements in the CEFR start-up test and presents the results by participants: temperature coefficient, sodium void reactivity, and swap reactivity. First, for measuring temperature coefficients, ten sets of data were obtained by increasing and decreasing the temperature. The control rod position is changed for each temperature to maintain the reactor as critical. Second, sodium void reactivity is measured by replacing a fuel SA with vacuum-sealed SA and searching for the critical position of control rods. Third, for measuring the swap reactivity, fuel subassembly is replaced by stainless subassembly, and stainless subassembly is switched with one fuel subassembly. Swap reactivities are measured in two different ways, with more than two control rods moving to find the criticality of the core in the ‘Multiple Rods’ case and only one control rod moving in the ‘Single Rod’ case. All three reactivities are obtained by combining control rod worth for changed rod position and criticality difference. The comparison shows that uncertainty of calculations, modeling errors, and inaccurately determined control assembly worth make it challenging to calculate the temperature coefficient precisely. Meanwhile, the void worth and the swap reactivity results have similar trends and show good agreement with measurement.