What is the energetic consequence of attempting to fuse iron nuclei in a massive star's core?

Answer

It consumes energy because iron has one of the highest binding energies per nucleon

Unlike fusion of lighter elements which releases energy (due to mass defect), fusing iron requires an input of energy because the iron nucleus is exceptionally stable, causing the star to lose its primary outward pressure source.

What is the energetic consequence of attempting to fuse iron nuclei in a massive star's core?
Corestarmassive