 power reactors cannot create nuclear explosions  like weapons. Second, "critical" describes a reactor at normal,  steady state operation, it does not mean an accident is occurring or  imminent. Finally, the "accident" is described in the movie as the  worst accident since Chernobyl. According to the UN, Chernobyl has  only caused 56 deaths to date and the final death toll for the  accident will be around 4,000. The destruction of a city the size of  Raccoon City and the death of all its inhabitants would be far worse  than the Chernobyl incident.