Abstract: A nuclear steam generator has a blowdown pump arranged to pump water from the blowdown lines through a filter for return to the steam generator. The piping is arranged so that the same pump may operate to reverse the direction of pumping through the blowdown line, whereby reverse circulation may be established during wet lay up of the steam generator. A blower is arranged to withdraw nitrogen from an upper elevation in the steam generator and injected into the blowdown line in combination with the pumped reverse circulation during wet lay up.