[Someone]

You don't need big craters to create a shadow. Plough the moon, turning over the dust in 20 cm wide and 10 cm high piles. At a square km per machine per week (I'm making that up, but it is less than a hectare per hour, and the world record is over 4 square km/day (http://www.guinnessworldrecords.com/records-1/ploughing-area...), likely on way better ground, but not nuclear-powered, either), that's 'only' 10,000 machine-years. Turn 10,000 nuclear warheads into crude nuclear engines, and you can do it within a few years.

I might help spending time choosing an area where you can avoid deep craters and have enough dust to form the piles.