If a tow truck ran over nuclear reactor what would happen to the reactor?

It is extremely improbable that a tow truck would collide with a nuclear reactor, and even if it did, the tow truck is unlikely to cause significant damage to the reactor. Nuclear power plants are designed with multiple layers of protection to ensure the safety of the reactor, including reinforced concrete containment buildings and emergency shutdown systems. The collision of a tow truck would not be able to penetrate the containment building and damage the reactor core.