Objects re-entering generally hit the ground at around terminal velocity, which is only a few hundred kph usually. The reactor core is surrounded by a very stur

Objects re-entering generally hit the ground at around terminal velocity, which is only a few hundred kph usually. The reactor core is surrounded by a very sturdy reinforced concrete containment structure which should be able to survive an impact of orbital debris. Additionally, the chance of orbital debris striking any particular location on Earth is nearly zero, so it's a bit foolish to over prepare for something that is less likely than winning the lottery several times in a row.