radiation ended up killing fish and crabs - not humans.
There was no enough intensity to just "kill", but mutations rate will be increased significantly for some time, until radionuclides will be finally deluted to below detection level by ocean. Sediments layer for few years after incident will contain higher level of nuclides, though it will be buried by later sediments quite soon. Maybe we will find new mutated crabs sometime, big and yummy, and name it "Fukushima crab". ;)
still thousands of square kilometers of Ukrainian territory are off limits - within the Chernobyl Exclusion Zone.
Do you ever visited Chernobyl zone? It is far from been lifeless. Looks like some harm from nuclear incident is almost nothing compared to harm from human exploitation of this territory, and ecosystem recovered to state that was hundreds of years ago, while there was no many humans living there.