I think the question is asking why nuclear power plants are safe? Nuclear power plants generate energy by nuclear fission. This process involves the reaction of atoms (like uranium) with other particles called neutrons. These "heavy" atoms then go unto break up into smaller atoms (like krypton and barium) and more neutrons. As this reaction goes on, more and more neutrons are made which results in a chain reaction (which is just a whole bunch of reactions). This nuclear fission process also creates heat, which is used to heat up water and produce steam. This is how we get energy from the reaction. The problem is that you also produce a lot of waste when this reaction happens. This waste goes into the water and lasts for thousands of years.

Researchers currently store this "nuclear waste" in big pools on the site of the nuclear reactors. These pools are full of cement, which are then lined with different metals to keep the waste water from going into the ground. As long as these pools don't crack or leak, the plant and waste are safe.

After hundreds of years, these pools can degrade and the nuclear waste can leak into the ground water which is very dangerous. Scientists are now trying to figure out different ways to store the waste, like burying it thousands of feet under the ground where there is no water for the waste to go into. Researchers are also trying to figure out better ways to limit the amount of waste produced.

Often in nuclear fission, only a small amount of the available uranium is used, so scientists are trying to find better ways of using all of the uranium. Hope this helps!