Innovative strategies for minor actinides using molten salt reactors

Within the framework of the ISAC (Innovative System for Actinides Conversion) project of the France Relance initiative, preliminary concepts of molten salt reactor capable of incinerating minor actinides have to be proposed in connection with prospective évolutions of the French nuclear fleet (stabilisation or reduction of the plutonium and americium inventory, minimization of the deep storage footprint, …) and contraints linked to the nuclear fuel cycle (plutonium and minor actinides inventories). The specificities of molten salt reactors will be exploited to design innovative transmutation strategies.
The postdoctoral fellow will be based in the reactor and fuel cycle physics unit of the IRESNE R&D institute at CEA Cadarache. He/she will develop expertise in neutronics, fuel physics, and in the design of Generation-IV reactors of the molten salt type.

Depletion calculation of nuclear reactor fuel using Monte Carlo method: moving towards a reference solution

Modern computers offer the possibility to use Monte-Carlo codes to get reference solutions to neutron transport problems. Nevertheless, such reference solutions are only accessible in stationary conditions for practical problems.
The proposed research work aims at exploring and testing methods to obtain a reference Monte-Carlo solution for fuel cycle quantities in depletion problems using present-day computing resources. Such a reference, obtained at a reasonable computational cost, would provide a better control over calculation biases and uncertainties in deterministic solutions typically used in the industry.
Studies will be performed using the Monte Carlo code TRIPOLI-4® coupled with the MENDEL deterministic depletion module. The post-doctoral fellow will perform extensive work on neutron leakage consideration in order to ensure criticality of the model, neutron flux and reaction rates normalization, control of the energy deposition in the different model regions, fine descriptions of the irradiation history, cross section stochastic temperature interpolation, as well as the impact of considering only a limited number of isotopes. Comparisons will be made with the results published by other groups using different approaches and Monte-Carlo codes .
The post-doctoral fellow will be positioned in a team of researchers/engineers in nuclear reactor physics. He/she will improve and deepen his/her knowledge of applied Monte-Carlo simulations as well as the code validation process.

Analysis of the SEFOR experiments for the multi-physics validation of fast reactor simulation tools :

In the Verification Validation and Uncertainty Quantification process of modern simulation tools, the validation phase relies mainly on the comparison between calculation and experimental results for the major quantities of interest. For neutronics, the experiment database focuses on measurements coming from zero power reactors for which the reference states does not require complex multi-physics modeling: isothermal state (very low power such as few hundreds of watts) and fresh fuel (un-irradiated).
However, the VVUQ of power reactor needs to go beyond zero power experiments and thus arises the necessity to apply a multi-physics VVUQ approach. This new frame requires the integration of phenomena from other disciplines outside of pure neutronics: temperature and density dependence of the main quantities of interest (keff, power distribution, and feedback coefficients), temperature field inside the pins as function of core power and irradiation.
Regarding Doppler Effect, the set of experiments held at the SEFOR facility in the 70’s is of major interest for the VVUQ process. This sodium cooled fast reactor fed with mixed oxide fuel was built in support of the US R&D program for indigenous code validation at the time.
Based on the available data, the proposed work focuses on core characterization using a fully neutronic/thermo-mechanic/thermalhydraulic process for both nominal and transient states based in high-fidelity modeling. In order to quantify the benefit of such approach, a step-by-step comparison will be done with the same results obtained by the traditional “chained approach” which assumes a weak dependence between the three mentioned disciplines.
The work will be performed using the last generation of simulation tools available at CEA.

Development of multiphysics tools dedicated to the modeling of FSR and associated studies.

The sodium group of DM2S (department of CEA Saclay) develops numerical coupling tools in order to realize accidental case studies (fast transient). The physical domains concerned are neutronics, thermo-hydraulics and mechanics. The subject of this post-doc deals within this framework.
The aim is to carry out several studies: the integration of a coupling within the CORPUS platform, to carry out studies in order to test (and introduce) in the coupling the impact of the deformation of the assemblies by the Temperature on the flow of liquid sodium, the use of the neutronic cross sections generated by the code APOLLO3, the study of other accidental cases, and extend the modeling to the subchannel and pin scales.