NUMERICAL BENCHMARK OF STRONGLY TO LOOSELY COUPLED ASSEMBLIES USING THE TRANSIENT FISSION MATRIX METHOD

Advances in computational methods have given rise to the study and simulation of different aspects of reactor behavior. As such, topics associated with high computational costs become feasible candidates for further investigation and one of them is reactor space-time kinetics (STK). Until recently, STK simulation and point kinetics approximation were limited to deterministic codes, with Monte Carlo codes being too costly to start with. However, recent developments in this area have allowed the use of certain methods in stochastic codes. One such technique is based on the Transient Fission Matrix (TFM) model, a hybrid method that uses a system response obtained through Monte Carlo and stored in fission and time matrices as input for deterministic calculations. The result enables a view of the STK in terms of neutron propagation probability and propagation time across the system. The TFM method was applied to a simple coupled core configuration to generate a numerical benchmark. The Serpent 2 Monte Carlo code was used for the stochastic part of the calculation. The configuration consists of two fuel assemblies placed in a light water tank, with a water blade of varying width between them. TFM, flux and fission results were obtained for varying water blade widths, ranging between 0 cm and 20 cm. The data is then used to analyze the behavior of the system, as well as the effects of the coupling between the two assemblies. As the assemblies move further apart, the system slowly transitions from two tightly coupled assemblies that essentially form a single core, to two almost independent cores. This study enables to produce a benchmark for future calculations and predefine an innovative way of designing high dominant ratio configurations, required for tackling Monte Carlo residual problems. An actual experimental program could be led in ad hoc zero power reactor (ZPR), such as the KUCA reactor of Kyoto University

NUMERICAL BENCHMARK OF STRONGLY TO LOOSELY COUPLED ASSEMBLIES USING THE TRANSIENT FISSION MATRIX METHOD

Advances in computational methods have given rise to the study and simulation of different aspects of reactor behavior. As such, topics associated with high computational costs become feasible candidates for further investigation and one of them is reactor space-time kinetics (STK). Until recently, STK simulation and point kinetics approximation were limited to deterministic codes, with Monte Carlo codes being too costly to start with. However, recent developments in this area have allowed the use of certain methods in stochastic codes. One such technique is based on the Transient Fission Matrix (TFM) model, a hybrid method that uses a system response obtained through Monte Carlo and stored in fission and time matrices as input for deterministic calculations. The result enables a view of the STK in terms of neutron propagation probability and propagation time across the system. The TFM method was applied to a simple coupled core configuration to generate a numerical benchmark. The Serpent 2 Monte Carlo code was used for the stochastic part of the calculation. The configuration consists of two fuel assemblies placed in a light water tank, with a water blade of varying width between them. TFM, flux and fission results were obtained for varying water blade widths, ranging between 0 cm and 20 cm. The data is then used to analyze the behavior of the system, as well as the effects of the coupling between the two assemblies. As the assemblies move further apart, the system slowly transitions from two tightly coupled assemblies that essentially form a single core, to two almost independent cores. This study enables to produce a benchmark for future calculations and predefine an innovative way of designing high dominant ratio configurations, required for tackling Monte Carlo residual problems. An actual experimental program could be led in ad hoc zero power reactor (ZPR), such as the KUCA reactor of Kyoto University

Application of the SPH method to account for the angular dependence of multigroup resonant cross sections in thermal reactor calculations

International audienceThe issue of the angular dependence of the multigroup total cross sections in the multigroup transport equation solution was recognized a long time ago. Only recently has its impacts on resonant self-shielding been identified. A viable solution for this problem is the superhomogenization (SPH) corrections. In the present work, two applications of the SPH method are presented, one applying to the APOLLO3 deterministic calculations with the multigroup cross sections condensed from the TRIPOLI-4 Monte Carlo simulation results and the other applying to a subgroup method based on the fine-structure equation. The numerical results show the effectiveness of the SPH method in dealing with this difficulty in both situations. This work also demonstrates that the subgroup method based on the fine-structure equation plus the SPH corrections is a practical, effective and accurate resonant self-shielding solution for the PWR fuel pin-cell and fuel assembly calculations

Scientific needs for a new generation critical facility at CEA: the ZEPHYR (Zero power Experimental PHYsics Reactor) ZPR

International audienceThe experimental programs performed in EOLE and MINERVE ZPRs for the last 40 years have been very fruitful for the understanding of LWR physical phenomena, and have generated a large experimental database on core physics. These fifty years old facilities could not comply with new post-Fukushima earthquakes safety criteria requirements, and the decision to close them was taken at the end of 2017. Therefore, the French Atomic and Alternative Energies Commission (CEA) started the project of building a new facility in Cadarache, called ZEPHYR (Zero power Experimental PHYsics Reactor), and designed for offering at least the same level of services as EOLE and MINERVE, and extending their capacities to several fast range applications. ZEPHYR is intended to be a modern RandD tool dedicated to reactor physics research (nuclear data, code validation in fundamental, mock-up and degraded/accidental configurations) open to the international community and Academia, whose functionalities and versatility will make it unique in the world. The scientific needs of a new critical facility were analyzed considering the foreseen needs of neutron calculation tools within 10-20 years, beside the unique experimental database provided by 50 years of experiments in EOLE and MINERVE to date. The major issues of current RandD needs address both nuclear data improvement for Gen2 to Gen-IV applications and innovative calculation tools (in particular non-equilibrium situations such as transients, 3D kinetics effects, as well as explicit instrumentation, and residual models). Analysis showed that the ZEPHYR project, versatile and flexible, with extended spectral capabilities, will be an essential element of the validation strategy by separate effects of future core physics calculation tools in a large range of spectra and configurations