Thanks to the combination of basic and applied research, INSPYRE brought significant advances on operational issues essential for the safety assessment and qualification of MOX fuels for future nuclear reactors, as well as on the simulation of their behaviour in reactor.
The new experimental and modelling results obtained constitute a significant and consistent contribution to the knowledge and understanding of the physical, thermal, chemical and mechanical properties of MOX fuels, the inert gas behaviour, the “Joint Oxyde-Gaine” (JOG) layer and the interaction between MOX and cladding at high temperature.
The thermodynamic modelling of the (U-Pu-Am-O) system was improved and the specific heat of MOX was evaluated at very high temperatures using atomic scale calculations. A new self-diffusion model for plutonium in MOX fuel and an associated mobility database was developed.
Concerning the inert gas behaviour, diffusion coefficients of Xe, Kr and He in fresh UO2 and MOX were determined using experimental techniques and modelling methods from the atomic to the grain scale. Various MOX fuel samples irradiated in past campaigns were characterised at the nanometre scale.
Complementary techniques and methods were combined to a precise control of materials and test conditions to determine mechanical properties and get further insight into the elementary processes governing their evolution under irradiation.
To improve the knowledge on the JOG layer formation, the transport properties of Cs and I were evaluated and the thermodynamic models of the Te-U, O-Te-U and Cs-Mo-Te-O systems were improved.
A significant part of these results were used to improve behaviour included in fuel performance codes. More physically justified correlations for were developed for the thermal and mechanical properties of MOX fuels including minor actinides as a function of all the parameters of interest in conditions relevant for GEN IV reactors. The modelling of fission gas and helium behaviour in MOX fuels were improved significantly thanks to the development of several physics-based models and their implementation in the SCIANTIX grain-scale module. An advanced micro-mechanical model suitable for both normal operation and off-normal conditions and including a description of the fuel rupture was also developed. Data obtained in the second half of the project are available to improve further the models and the codes.
The data obtained and models developed in the project were used to improve three European fuel performance codes: GERMINAL, MACROS and TRANSURANUS. The novel correlations for MOX thermal-mechanical properties obtained in the project were implemented in the codes and these were coupled with the SCIANTIX grain-scale module for inert gas behaviour.
The improved versions of the codes were then assessed on the simulation of the three past fast-neutron irradiation experiments SUPERFACT-1, RAPSODIE-I and NESTOR-3. The code validation against local and integral experimental data reveals harmonized predictions.
The new versions of the codes were used to simulate normal operation conditions in the ASTRID sodium fast reactor prototype, as well as transient conditions in the MYRRHA accelerator driven system. This enabled the evaluation of the safety margins of the fuel designs in the conditions considered.
These results were presented regularly to the project's User Group, which included designers of the ESNII prototypes, utility managers and fuel manufacturers.
Two schools dedicated to young researchers and three workshops were co-organized by INSPYRE partners, which contributed to present the results of the project to the nuclear fuel community. Exhibition material for general audience consisting of five posters on the energy mix, fission reactions, nuclear reactors, nuclear fuels and simulation codes and a video summarizing the objectives and results of INSPYRE were released.
