Swelling of U(Mo) dispersion fuel under irradiation – Non-destructive analyses of the SELENIUM plates

Surface engineering of the U(Mo) kernel surfaces is put forward by SCKCEN as a possible solution to U(Mo)-Al interaction in the Surface Engineering of Low ENrIched Uranium Molybdenum fuel (SELENIUM) program. The irradiation of 2 distinct (600 nm Si and 1000 nm ZrN coated) full size, flat fuel plates was performed in the BR2 reactor in 2012. The irradiation conditions were: 470 W/cm2 peak Beginning Of Life (BOL) power, with a 70% 235U peak burnup. The plates were successfully irradiated and did not show any pillowing at the end of the irradiation. This paper reports the results and interpretation of the non-destructive post-irradiation examinations that were performed on these fuel plates and derives a law for the fuel swelling evolution with burnup for this fuel type. It further reports additional PIE results obtained on fuel plates irradiated in campaigns in the past in order to allow a complete comparison with all results obtained under similar conditions. The fuel swelling is shown to evolve linearly with the fission density, with an increase in swelling rate around 2.5E21 f/cm3, which is associated with the restructuring of the fuel. A further increase in swelling rate, observed at the highest burnups, is discussed.