Protecting the nuke was a final tag along in series of changing plotlines.
Introducing Serizawa at the front of the story's first ten minutes when he discovered what appears to be Manda's remains should have made him the main character, using him basically as a history book was changing direction again. This movie is complete set of changing directions with not enough focus. As I said a J.O.A.M. This lack of focus and the uninspiring acting puts it in the boring category like it or not. A good film depends on a strong focused script, good acting, good directing, decent soundtracks, and good visuals, Godzilla 2014 strongest point is the last the rest are terribly weak to mediocre IMHO.
What does radiation have to do with anything? Godzilla represents two things: the living incarnation of the bombings Hiroshima and Nagasaki along with the dangers the Super Powers represent to the world and to Japan in particular, and the truly awesome untamable ferocity , kindness, and infinite power of nature. The appearance of Godzilla represents natures backlash at being messed with. The lack of radiation downgrades the danger and the meaning of the title character siginificantly. Godzilla isn't just some over sized scaly dinosaur, he's power the nature itself embodied in the nearly universal archetype of a god-like Dragon, and all the mood changes that go with that archetype. When we have troops being stupid or foolhardy enough to shoot small arms at this, its akin to saying troops should shoot at tornadoes, hurricanes, earth quakes, floods, falling asteroids, volcanic eruptions & their pyroclastics with small arms too. This movie added 7 meters to make up for a severe drop in the monster's dangers and symbolism.