But they don't have the stored energy density of fissile nuclear reactors; they have the stored energy density of a big particle accelerator. Shutting down a particle accelerator (either temporarily or permanently) is way easier than shutting down a fission pile, because a particle accelerator or fusion reactor would just dump the plasma into a graphite bed and dump the stored magnetic field energy into a bunch of large copper bars acting as big resistors.

EDIT: If you shot a hole in a fusion reactor, the cold air would immediately quench the plasma down to room temperature.

https://www.fusionindustryassociation.org/nrc-decision-separ...

Supporting letter from Helion Energy: https://www.nrc.gov/docs/ML2224/ML22243A083.pdf