This map reproduced from the UK Environment Agency shows the flood risk around the Sizewell plants. Flooding at nuclear power stations is a very International Atomic Energy Agency (IAEA) state that the flood risk should be one in 10,000 years.
Over the absolute minimum time that can be expected for nuclear material to be on the site (110 year) the probability of a 100 year event is 66.90%, 250 year event 35.65%, 1,000 year event 10.42% as shown in the graph on the right.
Even if flooded, the risk of a major leak should only be one in a thousand. The fact that there were major problems at more than one plant in Fukushima shows brings into question the way that risk assessments at nuclear plants are carried out.