The fission gas behaviors can be classified into single fission gas behavior and combined fission gas behavior with more interacting physics together. In this review, the fission gas behavior and relevant phenomena in different fuels for both models and experiments have been comprehensively overviewed, including fission gas release, gap/plenum pressure, grain growth, swelling, fission gas diffusion coefficients, and fuel cladding mechanical and chemical interactions under irradiations. Reactor structural integrity and nuclear safety are seriously affected by the fission gas behaviors and relevant physical phenomena in nuclear fuels. This study allowed assessing some aspects of the behaviour of LWR spent nuclear fuel during the first 300 years of storage time. Raman spectra were acquired for the first time on (U,Pu)O2 as a function of the self-irradiation dose. Thermal conductivity as measured by laser flash had already decreased by 40 % at 0.03 dpa, and no defects annealing was detected by differential scanning calorimetry at the temperatures foreseen for spent fuel storage. SEM observations highlighted the integrity of the fuel is preserved, while TEM evidenced the ingrowth of dislocation loops and He bubbles within the matrix. XRD showed a saturation of the lattice parameter increase around 0.3 %, while thermal desorption spectroscopy proved that the totality of the radiogenic He is still retained. Self-irradiated UO2 cumulating up to 0.41 dpa, the same reached by a LWR spent fuel after few centuries, was characterized periodically with a broad set of techniques. UO2 doped with 238Pu was also synthesised to study the accelerated effect of alpha-decays on fuel microstructure and thermophysical properties since alpha activity will be dominating in spent nuclear fuels for millenaries. Such material would allow studying through single effect studies the impact of the high burnup structure on the fuel behavior in and out of normal operation. In this work, the synthesis of dense UO2 and ThO2 with grains size down to 100 nm was designed. In particular it develops a rim structure also named high burnup structure characterized by the subdivision of the original micrometer sized grains into 100 nm grains. Due to the extreme environment in which it is operated, nuclear fuel shows changes of its microstructure and thermophysical properties.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |