An improved method to evaluate the “Joint Oxyde-Gaine” formation in (U,Pu)O₂ irradiated fuels using the GERMINAL V2 code coupled to Calphad thermodynamic computations

Abstract

In this work, two different thermodynamic softwares, ANGE using the TBASE database, and OPENCALPHAD using the TAF-ID (Thermodynamics of Advanced Fuels – International Database), have been integrated into the GERMINAL V2 fuel performance code (of the PLEIADES platform) in order to evaluate the chemical state of (U, Pu)O2 fuel and fission products in sodium cooled fast reactors. A model to calculate the composition and the thickness of the “Joint-Oxyde Gaine” (JOG) fission product layer in the fuel-clad gap has been developed. Five fuel pins with a final burnup ranging between 3.8 and 13.4% FIMA (Fissions per Initial Metal Atom) have been simulated, and the calculated width of the fission product layer have been compared with post irradiation examinations. The two different thermodynamic softwares have been compared in terms of computation time and predicted fuel-to-clad gap chemistry. The main elements and phases encountered in the fission productlayer have been identified, and the impact of the changing oxygen potential has been explored.

Thermodynamically Informed Nuclear Fuel Codes—A Review and Perspectives

“…The latter phenomena is unique to MOX fueled SFRs, whereby the increased fuel temperatures contribute to volatile and semi-volatile fission products migrating to the stainless steel cladding followed by condensation, forming a new phase typically called 'JOG' [65]. This phase is primarily comprised of molybednum and cesium oxides, in addition to others, as reported by Samuelsson et al [66]. The JOG layer affects heat transfer and may contribute to Fuel Cladding Chemical Interaction (FCCI), which increases the probability of fuel failure [12].…”

“…ANGE has historically been used in GERMINAL, which is essentially a modified version of SOLGASMIX [59], and uses the TBASE thermodynamic database [60,61]. The motivation for replacing ANGE with OPENCALPHAD in recent developments of GERMINAL is to use improved representations of irradiated fuel using the TAF-ID database [66].…”

“…Samuelsson et al report that 15 chemical elements in the TAF-ID were included in the GERMINAL-OPENCALPHAD coupling, whereby several chemical elements were grouped together based on some chemical similarities [66]. The motivation for grouping was twofold: (i) to reduce computational expense, and (ii) some chemical elements of interest in the fuel were not captured by the TAF-ID [66]. Some example surrogates that were considered by Samuelsson include grouping Ba and Sr (together to minimize costs), and I and Br (because Br is not in the TAF-ID) [66].…”

“…The motivation for grouping was twofold: (i) to reduce computational expense, and (ii) some chemical elements of interest in the fuel were not captured by the TAF-ID [66]. Some example surrogates that were considered by Samuelsson include grouping Ba and Sr (together to minimize costs), and I and Br (because Br is not in the TAF-ID) [66]. Overall, the use of OPENCALPHAD with the TAF-ID yielded improved predictions with respect to in-reactor experiments compared to predictions made with ANGE and TBASE [66].…”

“…Some example surrogates that were considered by Samuelsson include grouping Ba and Sr (together to minimize costs), and I and Br (because Br is not in the TAF-ID) [66]. Overall, the use of OPENCALPHAD with the TAF-ID yielded improved predictions with respect to in-reactor experiments compared to predictions made with ANGE and TBASE [66].…”