The problems with the Areva's system (besides the secret nature of the contract with TEPCO) is that the system is for treating the normal "contamination" in a normal nuclear power plant. At Fukushima, you have the reactors whose RPVs and Containment Vessels have been cracked or damaged, the fuel cores in 3 reactors melted with all kinds of junk inside and outside the RPVs and Containment Vessels, and seawater and fresh water poured over the molten mess which is now over 100,000 tonnes.
Will the Areva's system deliver? Areva's spokesperson says "Honestly it’s hard to say how it will work. We hope everything will be fine."
Now we know why TEPCO chose (if it had a choice) Areva: the same mode of operation. Try something anyway, see if it works, it it doesn't, well that's too bad, we'll try something else.
Actually, what else can they do at this point?
It is a costly way for trial and error, though.
From Washington Post (6/3/2011):
...... A potential turning point comes roughly two weeks from now, when Tepco plans to begin a treatment process in which water is sucked from the basement rooms and fed into a special tank, then treated with chemicals that eliminate its radioactivity. The process creates a byproduct of radioactive sludge, which is generally mixed with bitumen, poured into drums, then sealed and buried. The water itself can either be cycled back into reactors or discarded into the ocean.
The treatment system is being set up by Areva, a French company that uses the technology at its La Hague nuclear reprocessing plant, off the Normandy coast. Since 1997, Greenpeace — after taking water samples from La Hague’s discharge pipe — has made repeated claims that the supposedly decontaminated water in fact contains radioactivity levels above the regulatory limit.
The process “is not 100 percent, but it’s better than nothing,” Lochbaum said. “The alternative: you let the water simply evaporate and radioactivity carries to all parts far and wide.”
......Under normal circumstances, Areva’s system can decontaminate 50 tons of water per hour. But experts admit that it is hard to predict just how efficiently the system will handle water that contains not only radioactivity, but also debris, oil and salt. Water might need to be treated numerous times, not just once, before it can be dumped into the ocean.
“Normally the processing is done at small volumes, and you have carefully controlled chemistry,” Barrett said. “Here you have massive volumes and a very heterogeneous chemistry.”
“Honestly it’s hard to say how it will work,” said Patricia Marie, an Areva spokeswoman. “We hope everything will be fine.”