I suggest you should never run into a crater by surprise, really. Not into the danger area. For three reasons:
1.
Nuclear weapons make a big mess. If you are looking at a 200 m radius crater (~150 kt ground burst), you are looking at an event that left marks over an area bigger than an entire travel hex. Although that event was now at least 18 months ago, so grass and weeds have hidden the signs, your trained eye will notice things....
- six kilometres out, not a single window will remain. Now, that won't be unusual in areas that have been fought over, but if you pass through a village that's otherwise largely untouched, it should attract notice.
- about 3.5 kilometres out, the damage will be more characteristic of a major blast. Window frames will be blown in, doors will be blown off their hinges, roofs will be damaged. Homes will be inhabitable, though if you could find a building inspector, they would be condemned. The siding and roofs of steel-frame buildings will be bowed.
- about 2.5 kilometres out, houses will be flattened, and steel-frame buildings reduced to their frames. Only concrete structures will remain intact. 90% of trees will be blown down, which will be concealed by the weeds ... until you try to walk through such an area and find yourself tripping and stumbling over the trunks at every second step. Wood facing the blast will be charred and there will be widespread evidence of fires -- at this distance, the flash was intense enough to set dry wood alight.
- one kilometre from the crater, nothing will remain standing, unless you happen to find a reinforced concrete bunker.
You will know something big happened here before you run into the crater itself. You may actually go through the area without actually seeing the crater.
2.
Armies mark radioactive areas. For the safety of their own troops, both NATO and the Soviets would have marked dangerously radioactive areas soon after the strike. The NATO standard is a white inverted triangle with the word "ATOM" in black lettering. Now, these markings will be faded, tattered, and fallen, but you will still likely see some. And because of point 3 below, they'll be well outside the danger area.
http://navyadvancement.tpub.com/14325/c ... rs-373.htm
3.
Radioactivity goes away. You're not encountering chunks of hot plutonium here. Many radioactive elements decay much more quickly. The rule is 7/10: for each sevenfold increase in time, radioactivity declines by a factor of 10. 1000 rads per hour (immediately fatal) at T +1 becomes 100 rads/h after 7 hrs; after 2 days, 10 rads/hr, and so forth, so you're actually going to get something like 0.01 rads/hr after a couple of years. That's way above occupational health guidelines, but it's way below radiation sickness levels. So the danger area has shrunk. (In fact, the game rules make radiation a way bigger immediate danger than it should be. But that's okay: we expect radiation to be dangerous, and the game makes it dangerous in more immediate ways than it would really be, because dying of leukemia four years into the campaign might be realistic, but it's not how people want it to work.)
One other big effect, by the way, is that the 100 rads/hr fallout area from this strike, based on my current local weather, extends ... 87.8 km downwind. Meaning that you would have a swathe of abandoned villages and towns where people had either all died of radiation poisoning, or fled, or both, extending downwind from the crater in the direction of your choice, and that some of those villages will be marked with little white "ATOM" flags. Which is a great encounter to throw at players in place of a crater, imo: "Yes, you can scrounge this village if you like, but you might take a rad ... and by the way one of the things you find, in an upstairs bedroom, is a child's skeleton with a mouldering teddy bear, so here's a point of stress for your trouble."