Relative timing

Anna asked for a plot of the integrated neutron flux as a function of radius, for two cases, one in which all of the burn happens before the hot spot edge turns around and moves outward, and the other where most of the burn happens after the hot spot turns around.  My hunch was, we only have one of these cases appearing in our simulations.  This plot shows the hunch was correct:

I wondered if perhaps when we turned on the feedback (i.e. additional energy deposited into fuel from reactions, and energy leaving due to escaping radiation) this story could change.  Recall, however, that our code blows up when we add the feedback.  We do have the old mode (in which the feedback is a factor of 10 too small, and the run can finish before blowing up).  We refer to this as "Classic mode" (i.e. the mode with the fortuitous bug).   Using this I looked at the impact of feedback on these curves and found that the trend is entirely reversed:

I wanted to check if this might be an unexpected side effect of the bug, so I ran classic mode with both reactions and radiation off, just to make sure I captured the same behavior as the bug-free version.  Thankfully yes:

So it looks like the feedback causes the hot spot to turn around much earlier, in fact before peak burn is achieved.  I will make the integrated neutron flux plot with the case I trust, namely approx mode with reactions and radiation feedback off.