I was actually hoping they had removed the exploding cars. You know... I hoped they had done their homework and learned how nuclear reactors actually work and the ways they do fail. Don't get me wrong; shooting a car with a nuclear reactor would be bad, but it wouldn't mushroom cloud. At the very least, it would start leaking contaminated water around the area. An active one or one that goes on the fritz to pull the control rods to full power would start venting streams of super-heated highly pressured steam that would slice limbs and strip flesh from bone. Then once the actual clean water is vented, the heat would build inside the reactor until the super-heated reactor water pressures cause the reactor chamber containment to fail. This would release an explosive force (this is what happened at Chernobyl) that would destroy the vehicle and send shards of contaminated metal into the vicinity... Up to a mile away. At the same time, a burst cloud of super-heated steam would flash broil the flesh off anything within the immediate area and then the neutron particles released from the uncontrolled fission of the fuel would rain down into the internal cavities of anyone not behind some kind of shielding. These particles would get trapped inside the internal cavities of the unfortunate people in the area, bounce around inside (they have enough force to get through, but not enough to burst out... like a .22 round to the skull) to shred internal organs to mush.
So, instead of the mushroom clouds... ya'll could have had your enemies hole punched with radioactive metal, their skin broiled off, and their last moments spent lying in a pool of their own evacuated, liquefied organs with the area made highly radioactive for another 100+ years. But ya'll wanted cartoon mushroom clouds.