Wrong criticality when first nuclide in material has density of 0
Created by: ohnemax
This is a very specific error, and will very likely not affect many people. And probably it is an example for a wrongly written input file. However, it affected me and it took me some time to figure out what was going on, so I post it here.
When the first nuclide in a material has a density set to 0, criticality results show a very erratic behavior. A working example is attached.
Basically, the following material composition yields a combined k-effective of 0.76571 +/- 0.00025:
<material id="1" name="1.6% Fuel"> <temperature>900</temperature> <density units="g/cm3" value="10.31341" /> <nuclide ao="0.0" name="U234" /> <nuclide ao="0.00037503" name="U235" /> <nuclide ao="0.022625" name="U238" /> <nuclide ao="0.046007" name="O16" /> </material>
However, if the line with ao="0.0" for U234 is removed, it works fine. In this case criticality is 1.01150 +/- 0.00024. If the line is moved somewhere after a nuclide that has a non-zero density, it works fine, too. (criticality 1.01150).
I tested this with v0.10.0, compiled for cluster usage using OpenMPI 2.0.2. It occurs both for ENDF-B VII.0 and ENDF-B VIII cross section data sets.