Good Afternoon,
I am trying to find radial oxygen concentrations at EOL for a fast reactor’s MOX annular fuel pellet. The way I have been going about this problem is creating twenty regions of equal thickness, designating a new material in each (with the same compositions since it is homogeneous fuel at BOL). After the depletion runs are completed, I pulled the oxygen and plutonium concentrations at each region to graph with the intention of finding an equation to describe the radial distribution.
I have been getting some strange results, with a sharp downward spike of oxygen concentration in cell 5 (zero being the inside of the annulus). The graphed flux shows an increasing flux value over the radial distance in the fuel pellet, without any indication of why spikes occur in cell 5. I have done a mesh sensitivity study with 5, 10, and 15 regions and each seems to include this spike in the coarser regions. There does not seem to be a physical reason why these results occur. Do you have any advice on how to close in on why this is occurring?
HI,
It is very intersting and if you allow me to think loudely (probably i’m just saying wrong things) because it seems strange that you get such like spike of Oxygen in specific place.
Did you try to reduce the depletion period to see what is happening at smaller time scale? if this evolve vs time or it is just a specific shape occuring at that place (it could be a numerical artefact or scale effect)
can you get the flux distribution with major component (mainly intermediate and fast neutrons) to compare with Oxygen capture cross section. You can also check N and C isotopes evolution, perhaps it may be correlated by some neutron capture reaction !!! (it will depends if you are using natural oxygen or directly the nuclide O16)
This effect occurs at all depletion periods, and always in the fifth cell in a 20 region model. Each cell’s concentrations increase/decrease linearly, which is why this effect is odd. The flux distribution in terms of intermediate and fast linearly increase through the cells, increasing from the inside radius to the outer. Nothing significant pops out in the cross sections, they are fairly uniform at the energy ranges seen in the model. The MOX fuel composition used only contains O16, which makes the observed effects extremely strange.
