The development of GEN-IV fast reactor technology at an industrial scale will need significant improvement of nuclear data and related uncertainties to cope with awaited target uncertainties. Zero Power Facilities enable to answer GEN IV experiments are sparse. In France, MASURCA ZPR and the future ZEPHYR multipurpose ZPR to be built in Cadarache belong to those facilities. For this latest one, fast/thermal coupled configurations performed in MINERVE during the 1970's have been recently revisited using modern calculation tools. The principle of a fast zone fed by a thermal booster, known from decades as the concept of coupled cores regained interest in recent years. This paper describes the concept of fast/thermal coupled core, a deeper description of the physical characteristics of the adaptation zone, and its use in the improvement of fast-spectrum nuclear data thanks to integral experiments. An optimized configuration is then presented. The preliminary design phase is performed using deterministic tools, a posteriori validated against a full Monte Carlo calculation. Particular attention is paid on the impact of the buffer zone on the spectral characteristics in the oscillation channel, as well as the sample mass characteristics required to ensure a proper signal analysis. Moreover, preliminary studies dedicated to the experimental realization of such a configuration are described, including the reactivity stability in case of an accidental flooding of the fast central zone.
In neutron chain systems with material symmetries, various k-eigenvalues of the neutron balance equation beyond the dominant one may be degenerate. Eigenfunctions can be partitioned into several classes according to their invariance properties with respect to the symmetry operations (mirror symmetries and rotations) keeping the material distribution in the system unchanged. Their calculation can be limited to a fraction of the system (sector) provided that innovative boundary conditions matching the symmetry classes are used, and whole-system eigenfunctions can then be unfolded from the solutions obtained over the sector. With power iteration as the method for searching k-eigenvalues, this use of the material symmetries to split the global problem into a variety of smaller-sized problems has several computational advantages: lower computation times and memory requirements, increased dominance ratios, lowered possible degeneracies in each subproblem, and possible parallel (separated) treatment of the subproblems. The implementation is discussed in a companion paper using diffusion and transport theories.
In neutron chain systems with material symmetries, various k-eigenvalues of the neutron balance equation beyond the dominant one may be degenerated. As shown in a companion paper, the power iteration method can be used to compute higher eigenfunctions in symmetric systems, provided that the global problem is partitioned into symmetry class-related lower-sized problems with appropriate boundary conditions. Those boundary conditions have been implemented in the diffusion solver of the ERANOS code system in rectangular geometry and within the framework of a discontinuous Galerkin spatial approximation of the multigroup discrete ordinates transport equation in the SNATCH solver. Numerical results in homogeneous geometry are provided for verification purposes, as well as the first eigenfunctions of the Takeda benchmarks. Finally, the transport effect on the first flux harmonics for an industrial-sized reactor ZPPR-18 is discussed.
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