The announcement comes just days before the International Olympic Committee decides whether Tokyo - 140 miles from the plant - will host the 2020 Olympic Games and the government is keen to show the crisis is under control. Madrid and Istanbul are the rival candidates.
Prime Minister Shinzo Abe said: "The world is watching to see if we can carry out the decommissioning of the Fukushima nuclear power plant, including addressing the contaminated water issues."
However, the government intervention represents only a tiny slice of the response to the Fukushima crisis, triggered by the earthquake and tsunami which hit Japan in March 2011 and caused the meltdown of reactors at the plant.
The clean-up, including decommissioning the ruined reactors, will take decades.
There are concerns that the latest measures do not address the full problem of water management at the plant or the bigger issue of decommissioning.
The sensitive job of removing spent fuel rods is to start in the coming months and the fate of the plant's operator, Tokyo Electric Power Co (Tepco), also remains unclear, as does the question of who will eventually foot the bill - Japanese taxpayers, or embattled Tepco.