Nuclear simulation codes have been rewritten to run in more modern languages.[0] Not only is the DOE not required by law to detonate a nuke to make non-technical changes to their codes, they have invested many billions of dollars into programs for validating entirely new codes without nuclear testing, such as the NIF.[1]

[0] https://www.sciencedirect.com/science/article/abs/pii/S03064...

[1] https://lasers.llnl.gov/science/nif-stockpile-stewardship#:~...

Let's apply some critical thinking.

If the F90 code works it gives the same answers as the F77 code, no need to test any bombs.

Move along folks, nothing more to see.

my first job: tend to 70k lines F77 on RSX-11M (pdp/11-44 pair)

interfaced to it with SunOS 4 & C

enjoyed my time with SunOS, not so much with RSX

If there actually were a Fortran 77 compiler industry, it would deserve to die.