what is Shukhov's reaction to his punishment? why does he react this way?

Shukhov at heart is an existentialist. Like Sisyphus, whose punishment is the classical underworld is to continually push a rock up a hill, only to have it roll to the bottom to be pushed up again, Shukhov finds freedom in the certainty of his punishment. If punishment is always expected it hence becomes a way of life. Shukhov can relegate punishment to just part of his life in prison, no more concerning than ambient noise.