The Fukushima accident was half a decade ago now, the ocean is so large, how would one reactor have a worth impact?

Question: The Fukushima accident was half a decade ago now, the ocean is so large, how would one reactor have a worth impact?
- Keywords:
  Fukushima,
  nuclear
Asked by JohnCena to Keith on 10 Nov 2015. This question was also asked by EueBear_69.
- Keith Franklin answered on 10 Nov 2015:
  
  It is a very good question – and the answer is that it doesn’t have an effect on the ocean. The amount of pollution reaching the sea is so small, and the ocean is so big, once you are 300 metres off shore you can no longer detect anything.
  
  The work that needs to be done is to clean out the buildings which have melted nuclear fuel in them – that is why you need clever gadgets to look inside and then robotic arms to take the material out.

Question: The Fukushima accident was half a decade ago now, the ocean is so large, how would one reactor have a worth impact?