In my world (a very soft sci-fi world), humans live beneath the surface in a large planet that is largely inhospitable on the surface. It's not Earth. The hollow planet is kind of like Swiss cheese in that it's mostly solid but there are large "burrows" where humans live and they connect to one another through large tunnels. 300 years prior in this world's history, a burrow launched a nuclear bomb at another burrow during a war. My idea is that after this, the burrow that had a bomb dropped on it was sealed off out of fear that the nuclear waste would travel to the rest.
Is this a plausible reaction? My line of thinking is that since they are underground, there are less places for the fallout to go compared to a planet where the people inhabit the surface. In addition, would sealing off this contaminated burrow even prevent further damage from reaching the other burrows?
Additional information: this bomb was around the beginning of the world's foray into nuclear technology. Its strength was 21 kt.
On average, the distance between these burrows is about 3,500 miles. The tunnels that connect them are not straight. They curve, sometimes moving up and down.
There is volcanic activity on the surface, though not a lot above the burrow that suffered the attack.