People at Umi-Labo ("sea laboratory") in Iwaki City, a non-profit citizens' group, went near TEPCO's Hirono Thermal Power Plant, Fukushima II (Daini) Nuclear Power Plant, and Fukushima I (Daiichi) Nuclear Power Plant for the second time on April 27, 2014 on a fishing boat that had survived the March 11, 2011 tsunami. They came as close as 1.5 kilometer from Fukushima I Nuclear Power Plant.
Apparently, there is no restriction that prohibits anyone from going near Fukushima I Nuclear Power Plant by boat. So far, I only know of this group that has done that. No research institute nor nuclear expert (other than IAEA) has bothered.
According to Mainichi Shinbun (5/7/2014) reporting the trip:
The air radiation level on the boat at 1.5 kilometer from Fukushima I NPP was 0.05 microsievert/hour, surprisingly low, due to the shielding effect of water (ocean).
The ocean soil sample taken at Fukushima I NPP contained 417 Bq/Kg of radioactive cesium, whereas the ocean soil sample taken off Iwaki City had 287 Bq/Kg.
In the Mainichi article, the captain of the fishing boat says, "Isn't it amazing, how small Fukushima I NPP looks from the ocean? And this small plant is troubling the world." He had saved his boat by riding the tsunami waves on March 11, 2011.