K.B. Khan

Densification behaviour of UO2 in six different atmospheres

Abstract The shrinkage behaviour of UO 2 has been studied using a dilatometer in various atmospheres of Ar, Ar–8%H 2 , vacuum, CO 2 , commercial N 2 and N 2 +1000 ppm of O 2 . The onset of shrinkage occurs at around 300–400 °C lower in oxidizing atmospheres such as CO 2 , commercial N 2 and N 2 +1000 ppm O 2 compared to that in reducing or inert atmospheres. Shrinkage behaviour of UO 2 is almost identical in Ar, Ar–8%H 2 and vacuum. The shrinkage in N 2 +1000 ppm O 2 begins at a lower temperature than that in the commercial N 2 . The mechanism of sintering in the reducing, inert and vacuum atmospheres is explained by diffusion of uranium vacancies and that in the oxidizing atmospheres by cluster formation.

Densification behaviour and sintering kinetics of PuO2 pellets

Abstract The sintering behaviour of PuO 2 pellets has been studied using a dilatometer in inert, reducing and oxidising atmospheres. The shrinkage rate was found to be maximum for pellets sintered in Ar–8% H 2 atmosphere. The mechanism for the initial stage of sintering was determined using rate controlled sintering (RCS) technique and was found to be volume diffusion for both inert and reducing atmospheres. The activation energy for the initial stages of sintering was found to be 210 and 159 kJ/mol for Ar and Ar–8% H 2 atmospheres, respectively. The mechanism for the sintering in oxidising atmospheres could not be evaluated using RCS technique.

Densification behaviour of UO2–50%PuO2 pellets by dilatometry

Abstract The sintering behaviour of UO 2 –50%PuO 2 pellets has been studied using a dilatometer in inert, reducing and oxidising atmospheres. The shrinkage begins at a much lower temperature in oxidising atmosphere such as CO 2 and commercial N 2 . The shrinkage rate was found to be maximum for pellets sintered in N 2 atmosphere. The mechanism for the initial stage of sintering was found to be volume diffusion for both oxidising and reducing atmospheres. The activation energy for the initial stages of sintering was found to be 365 and 133 kJ/mol for Ar–8%H 2 and CO 2 atmospheres, respectively. The activation energy obtained using the Dorn method matches well with that obtained using the rate controlled sintering process. The lower activation energy obtained in the oxidising atmosphere is explained with the help of models available in the literature.

Sintering studies on UO2–PuO2 pellets with varying PuO2 content using dilatometry

Abstract The sintering behaviour of UO 2 , PuO 2 , UO 2 –20%PuO 2 , UO 2 –50%PuO 2 and UO 2 –76%PuO 2 pellets have been studied using a dilatometer in inert, reducing and oxidizing atmospheres. The onset of shrinkage occurs by about 400°C lower in oxidizing atmosphere such as CO 2 and commercial N 2 than that occurs in reducing atmosphere. PuO 2 and UO 2 –76%PuO 2 showed an expansion on heating in Ar at ∼1000°C. UO 2 –20%PuO 2 pellet sinters slightly better in Ar than in Ar–8%H 2 . From the shrinkage rate curves, it was found that the maximum shrinkage rate occurs in commercial nitrogen atmosphere for UO 2 –50%PuO 2 . For the other compositions, the maximum shrinkage rate was observed for Ar atmosphere. The sintering behaviour of above mentioned pellets was discussed with the help of point defect model and the possible mechanisms were suggested.

Densification behaviour of ThO2–PuO2 pellets with varying PuO2 content using dilatometry

Abstract The shrinkage behaviour of ThO 2 , ThO 2 –30%PuO 2 , ThO 2 –50%PuO 2 and ThO 2 –75%PuO 2 pellets has been studied using a dilatometer in inert (Ar) and reducing atmospheres (Ar–8%H 2 ). The effects of dopants of CaO and Nb 2 O 5 on shrinkage of the oxides of the above Pu/(Pu+Th) ratios were also studied. Out of the two dopants studied, CaO was found to give larger shrinkage for all the Pu/(Pu+Th) ratios covered in this study. It was also found that the shrinkage was marginally larger in Ar–8%H 2 than in Ar atmosphere. Addition of PuO 2 to ThO 2 enhanced sintering. This was found to be true for both the dopants. During the sintering of ThO 2 , a prominent peak was observed in the shrinkage curve at around 100–300 °C. This peak was attributed to the pressure increase of the trapped gases which subsequently release at high temperatures.

Bulk characterization of (U, Pu) mixed carbide fuel for distribution of plutonium

Homogeneous distribution of plutonium in (U, Pu) mixed fuels is important from fuel performance as well as reprocessing point of view. Radiation imaging and assay techniques are employed for the detection of Pu rich agglomerates in the fuel. A simulation study of radiation transport was carried out to analyse the technique of autoradiography so as to estimate the minimum detectability of Pu agglomerates in MC fuel with nominal PuC content of 70% using Monte Carlo simulations.