The Oskarshamn plant is a boiling-water reactor, just like the Fukushima plants in Japan that failed so disastrously two years ago. (For more on what a boiling-water reactor is and how it works, check out our explainer.) In brief, a boiling-water reactor uses thousands of thin tubes full of fuel, commonly known as fuel rods, which contain the little pellets that feed the nuclear reaction. These rods are absurdly, dangerously hot, and so are kept submerged in cooling water. Water has to be cycled in and out of the plant continuously as it heats up, which is why nuclear plants are so often near large sources of water like lakes, rivers, and oceans. But you know what also likes large sources of water? Marine life.