Chemistry of the nuclear fuel-coolant interaction in LFRs
The Lead-cooled Fast Reactor (LFR) is a nuclear reactor that is cooled with liquid metal, more specifically liquid lead or a liquid eutectic mixture of lead and bismuth. One of the issues in the safety assessment procedure is which chemistry can take place in case of a cladding breach, in which the coolant can come into contact with the fuel or the fission products.
Although nitride is a fuel candidate, (U,Pu)O2 mixed oxide (MOX) fuels are currently the preferred option for various LFR designs in Europe since substantial experience has already been gained in terms of fabrication, reactor operation, reprocessing, and risk assessment. The plutonium concentration in the (U,Pu)O2 fast reactor fuel is typically of the order of 20wt%.
A thorough assessment of the potential chemistry of the multi-element (Pb,Bi)-(U,Pu,FP)-O system (FP=fission products) is crucial in the prediction on possible issues like local stress inside the fuel pin or release of fission products into the primary coolant vessel. This chemistry is studied in our laboratories using diffraction techniques (X-rays, neutrons), spectroscopy and calorimetry. The experimental data is used as input for thermodynamic models.
Recently, we reported on the chemistry between the so-called JOG-layer and lead. The JOG-layer is a layer that is formed at the outer rim of the fuel pin at a burnup that can typically be reached in LFRs, so it would be the first layer to come into contact after clad breach. The JOG-layer contains oxide and iodide phases, containing a.o. the elements Cs, Mo and I.
Curious? More on our recent results can be found in the following article:
A. van Hattem, J. Vlieland, R. Dankelman, M.A. Thijs, G. Wallez, K. Dardenne, J. Rothe, R.J.M. Konings, A.L. Smith (2023). Structural Studies and Thermal Analysis in the Cs2MoO4–PbMoO4 System with Elucidation of β-Cs2Pb(MoO4)2. Inorganic Chemistry, 62(18), 6981-6992.
A. van Hattem, D. Alders, R.J.M. Konings, A.L. Smith (2023). Ternary System CsI–PbI2–BiI3 and Thermodynamic Stability of Cesium Metal Halide Perovskites. The Journal of Physical Chemistry C, doi.org/10.1021/acs.jpcc.3c02696