Transport properties of I, Te and Xe in thoria–urania SIMFUEL

Thermodynamic and transport properties of thoria–urania fuel of Advanced Heavy Water Reactor

“…Their results showed two to five times drop in Xe diffusivity in the doped samples. Cation or anion vacancy not augmenting the transport, these authors made similar conclusion as that of Matzke et al In a recent study in this laboratory it has been shown that increase of both cation and anion vacancies augments Xe transport substantially [36]. The vacancies were introduced in the simulated fuel (ThO 2 -2 mol% UO 2 containing fission products corroborating to 20 GWD ton À1 burnup) by evaporation of magnesia component in thoria and also of SrO/ BaO components from the added alkaline earth fps in the SIMFUEL during its long sintering at 1900 K in flowing argon containing 8% hydrogen.…”

“…The barrier energy of 478 kJ mol À1 obtained by Shiba et al [40] can be compared with those reported for urania by different authors: 407 kJ mol À1 by Miekeley and Felix [42], 376 kJ mol À1 by Matzke [20] and 644 kJ mol À1 by Prussin et al [43] Shiba et al explained the observed barrier energy by invoking that Xe transport occurred through tetra vacancy mechanism [44]. Trivacancy introduction through evaporation of alkaline earth oxides in the SIMFUEL resulted in reduction in barrier energy as well as increase in frequency factor for Xe diffusion [36] (Table 5).…”

Trapping and diffusion of fission products in ThO2 and CeO2

“…Yun et al [30] have calculated the binding energy of a single V O separated by Xe-vacancy complexes in ThO 2 using the GGA method and suggested Xe diffusion by the vacancy-assisted mechanism is unfavorable. Recently, the work performed by Shirsat et al [11] showed that the vacancies play an important role in Xe migration in ThO 2 , and the increase of vacancy concentration decreases the energy barrier, indicative of a vacancy-assisted mechanism. Also, the migration energy of 1.96 eV reported in their work is in excellent agreement with our result of 1.9 eV.…”

“…Due to the importance of thoria in the nuclear industry, a number of investigations on the release and transport behavior of fission gases and volatiles in thoria and thoria-based fuels have been reported; [4,[10][11][12][13][14][15][16] however, significant discrepancies exist in the migration energy and diffusion mechanism [10]. For example, Shiba [17] reported a high energy barrier of 4.95 eV for xenon release from thoria-6% urania (UO 2 ) and suggested that Xe transport occurred through a tetra-vacancy mechanism.…”

“…Naik [18] reported an activation energy of 2.48 eV for Xe migration in thoria-1% urania, while they suggested the migration occurred through interstitial motion. Recently, Shirsat et al [11] studied Xe transport in a solid solution of thoria-2% urania and obtained a migration energy of 1.9 eV. They also suggested that the increase in vacancy concentration decreases the migration energy, indicative of a vacancy-assisted mechanism.…”