Not actually sure on the spelling, actually...sorry about that.
Might be "wyrm", "worm" or "wurm". But yes, you are correct in that it is usually something draconic.
But the main idea here is that it is a giant, pallid, squishy, burrowing thing.
I guess I just wanted to point out that the description provides a pretty clear general image. The details are, naturally, left pretty vague, as each A-bomb is a unique mutant monster, but even the specifics they give aren't very helpful (fists the size of boulders, incisors as long as a horse's leg).
A lot of people just seemed to not read the description of it, so I figured I'd just point 'em to it.