Complex sentence: The Irish Sea was contaminated by radioactive caesium-137 from the former Sellafield nuclear fuel processing plant and nuclear accidents, such as the one at the Fukushima Daiichi Nuclear Power Plant in 2011, may also cause radioactive material to seep into the sea.
Split into simpler sentences: The Irish Sea was contaminated by radioactive caesium-137 from the former Sellafield nuclear fuel processing plant. Nuclear accidents as at the Fukushima Daiichi Nuclear Power Plant in 2011 may pollute the sea.