Poster sessions will be run during the afternoon breaks (3:20 PM – 4:00 PM Tuesday and Wednesday in PJ Hall, Main Arts Building) of the conference. A Teams meeting will be set up for each poster allowing presenters to answer questions from online attendees and those in Bangor. Posters may also be viewed on the conference website.

A new laser heating setup for the measurement of noble gases diffusion in nuclear materials

Denis Horlait

Eric Gilabert, Bertrand Thomas, Rémi Faure
Université de Bordeaux, CNRS, CENBG-IN2P3, F-33170 Gradignan, France

The noble gases helium, krypton and xenon are generated or implanted in many materials employed in or developed for fission or fusion nuclear reactors (e.g. UO2, neutron absorbers, high-level waste matrices, etc.). Taking the example of the usual fission nuclear fuel UO2, the in-pile generation of noble gases is greatly responsible for the unfavorable microstructure and thermal properties evolutions of the fuel. However, the underlying mechanisms governing the behavior of these gaseous elements in UO2 are so far not entirely understood and are almost unknown for the GenIV fuel candidates. Consequently, the diffusion mechanisms and kinetics of noble gases in nuclear materials are paramount to determine for a comprehensive range of experimental parameters. These are however often quite complex to access experimentally, especially when looking to low concentrations to avoid the formation of gas bubbles or defect aggregates.
At our laboratory the quantification of noble gases diffusing out of materials is made possible down to as low as few 107 atoms thanks to advanced gas purification and mass spectrometry techniques. However our investigations were up until recently limited by the actual conventional vacuum furnace used for samples heating (maximum temperature of 1400°C, imprecise control of temperature, impossibility to control and impose oxygen partial pressure (pO2), etc.).
To overcome these limitations, a new heating line has recently been implemented. The latter is based on the use of a high-power laser beam able to quasi-instantaneously and homogeneously heat the samples to controlled temperatures in the range of 600 to 2200°C, with a limited heating of the sample holding components only to preserve a sufficient temperature homogeneity across the sample. Moreover, an oxygen tank is also connected to the ultra-high vacuum line in order to input to the system controlled amounts of O2. 
The proposed poster aims to present the features of this new experimental line and the unique new possibilities of investigation brought by this new setup. A recent case study will also be presented: O2 additions effects on Kr diffusion kinetics in UO2±x.

Progress in Coupling Computational Thermodynamics and Computational Fluid Dynamics to Support Molten Salt Reactors

Nikolas Scuro

Faculty of Energy Systems and Nuclear Science, Ontario Tech University, Oshawa, ON, Canada

Progress in multiphysics coupling between computational thermodynamics and Computational Fluid Dynamics (CFD) of a Molten Salt Fast Reactor primary loop will be presented in support of the SAMOSAFER project. Under abnormal conditions, such as overheating or undercooling, the chemical composition of the salt may change and phase transformations may take place, which are important to understand in the context of performance and safety. The influence of fission products needs to be considered in the CFD analysis, which may precipitate, boil, or remain soluble in the salt — computational thermodynamics are intended to perform these calculations. The CFD and chemical equilibrium calculations will be performed using the open-source libraries OpenFOAM and Thermochimica, respectively. The Joint Research Centre (JRC) molten salt database will be used as input to thermodynamic calculations. Preliminary results in single-phase and multi-phase flow in the MSFR will be presented. Also, the results of a recent benchmarking campaign to verify Thermochimica when using the JRC database with respect to commercial software will be summarized.

Thermochemical studies into the JOG-coolant system Pb-(Cs,Mo)-O for Lead-cooled Fast Reactors

Andries van Hatten

Delft University of Technology, Faculty of Applied Sciences, Radiation Science & Technology Department, Mekelweg 15, 2628JB, Delft, The Netherlands bEuropean Commision, Joint Research Centre-Karlsruhe (JRC), P.O. Box 2340, D-76125, Karslruhe, Germany

The Lead cooled fast reactor (LFR) is one of the next generation nuclear reactor types selected by the Generation IV International Forum (GIF) [1] . The current reference fuel in LFRs is (U,Pu)O2 cooled by either lead (Pb) or lead-bismuth eutectic (LBE) coolant. During irradiation, numerous  fission products (FPs) are generated that can be classified in several categories: FPs in solid solution in the fuel matrix, FPs forming metallic precipitates, gaseous and volatile FPs, or oxide precipitates. Among these, the volatile FPs (e.g. Cs, I, Mo, Te) migrate towards the rim of the fuel pellet, where they accumulate in the space between the fuel and cladding, forming at high burn-up a so-called Joint-Oxyde Gaine (JOG) layer of a few hundred micrometres. Typically, the JOG phase contains Cs2MoO4 (the major constituent), CsI, Cs2Te etc. [2].

Risk analysis of the LFR involves the assessment of the consequences of a clad breach, in which case the coolant (Pb, LBE) will interact with the fuel (U,Pu)O2 and the surrounding JOG (mainly Cs2MoO4). As part of the PASCAL H2020 European Project [3], we have performed studies into the JOG-coolant interaction. After an extensive literature review, we have initiated experimental studies into the interaction products between Pb and Cs2MoO4. Depending on the oxygen potential, Pb and Mo can form compounds like PbMoO4 and Pb2MoO5 [4]. We have studied the Thermodynamics of Nuclear Fuel between the latter phases and simulated JOG phases (Cs2MoO4) using solid state synthesis and post-characterization by X-ray diffraction. To get further insight into the thermochemistry of these systems, relevant mixtures were moreover made in the whole composition range between Cs2MoO4 and PbMoO4, and measured with Differential Scanning Calorimetry (DSC). Furthermore, solution calorimetry was applied to obtain the enthalpy of formation of Cs2Pb(MoO4)2, a quaternary phase formed upon reaction between Cs2MoO4 and PbMoO4. Relevant sections of the PbO-Cs2O-MoO3 pseudo-ternary phase diagram are thus being assessed experimentally in our work and unexplored regions are subjected to new research.

Combining data from literature with obtained experimental data, CALPHAD models will be developed in the near future. Our experimental results and thermodynamic modelling will in the end enhance evidence-based risk analysis of accidental scenarios and the aftermath of JOG-coolant interaction in the LFR.

[1] A. Alemberti et al. “Overview of lead-cooled fast reactor activities.” Progress in Nuclear Energy 77 (2014): 300-307
[2] M. Pelletier, Y. Guerin, 2020. Chapter 2.03 Fuel performance of Fast Spectrum Oxide Fuel. In: Konings, R.J.M. & Stoller R. (Eds.) Comprehensive Nuclear Materials 2nd edition, Elsevier, Volume 2, pp. 72-105
[4] W. Cairang, et al. “”Oxidation mechanism of refractory Molybdenum exposed to oxygen-saturated lead-bismuth eutectic at 600 C.”” Corrosion Science 179 (2021): 109132.