Numerical validation of the APOLLO3®-FR deterministic calculation route based on a simplified Phenix configuration.

• APOLLO-3-FR is a deterministic neutronics scheme utilized for comprehensive analysis of power sodium fast reactors/ APOLLO-3-FR shows good agreement with a reference calculation for differential control rod worth • It reveals low discrepancies for main integrated reaction rates, ranging from 0.04% to 0.62%, compared to the reference / APOLLO-3-FR shows acceptable accuracy for further experimental validation studies Design and development of future reactor technologies rely on an intensive use of computational tools for which confidence levels have to be quantified for each targeted quantity of interest. Validation process and uncertainty quantification of such tools must rely on both numerical and experimental data. While zero-power experiments have been widely used in the past, notably for the Sodium-Cooled Fast Reactor (SFR), increased computing power offers the possibility of modeling increasingly complex phenomena. On such a basis, available data from power reactors operation, such as those of the Phenix reactor, can be considered for exhaustive experimental validation of computational tools. In the case of a multi-physic approach, observed phenomena result from multiple factors and origins, each of which may introduce its own modeling bias. Therefore, the decomposition of inherent biases in computational tools for each involved phenomenon is essential to master the accuracy level of any predictive simulation. For neutronics, using deterministic route capabilities offered by the APOLLO3® multi-purpose code, the numerical validation has been performed for each step, from the elementary level (cell, lattice) up to a "Phenix-like" configuration in order to quantify the associated residual biases for the relevant quantities of interest. In the frame of the deterministic approach used here, the APOLLO3®-FR calculation scheme is based on a traditional two-step (lattice/core) assumption. Each step relies on different numerical methods with different parameters whose influence has been identify and quantified. The best set of numerical parameters that lowers the discrepancy compared to the reference calculation tool TRIPOLI-4® (Monte Carlo code) has been determined. It shows that at the 2D lattice scale, before and after homogenization/condensation process, an acceptable accuracy is reached for a further use in 3D core calculation for which validation focuses mainly on the differential control rod worth and reaction rates distribution. Regarding the differential control rod worth, APOLLO3®-FR shows a good agreement with Monte-Carlo reference (<2σ of the TRIPOLI-4® statistical uncertainty). The 239Pu fission and 238U capture rates computed with the deterministic scheme show that the discrepancy with TRIPOLI-4® is within 0.04 % and 0.62 % in global for inner core and outer core zones. These discrepancies are acceptable for further in-depth studies, for instance, fuel depletion or multiphysics analysis, using a more realistic configuration of the Phenix core. [ABSTRACT FROM AUTHOR]

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