Here's their statement as reported by the PanOrient news:
A most welcome development. Let's hope the Japanese don't kick them out.
“Since the beginning of the Fukushima nuclear crisis, the authorities have consistently appeared to underestimate both the risks and extent of radioactive contamination. We have come to Fukushima to bear witness to the impacts of this crisis and to provide some independent insight into the resulting radioactive contamination”, said Greenpeace team leader and radioactivity safety advisor Jan van de Putte in a statement.
“By providing honest, transparent and independent analysis of the threats to public health, we aim to provide an alternative to the often contradictory information released by nuclear regulators in the two weeks since the Fukushima disaster began unfolding.”
“Any attempt by authorities to play down the effects of the current crisis should be considered a dangerous deceit. In addition to coming clean on the true dangers of nuclear power, the smartest move for governments around the world is heavily invest in energy efficiency, and redouble their efforts to harness safe and secure renewable energy sources.”