Some people made something called plutonium. Plutonium is a really strong and powerful stuff that can be used to make really big and strong bombs that could hurt a lot of people.
The people who made plutonium, some a long time ago, did not do a very good job of keeping it safe or telling other people about it. They even did some really bad things with it that made people sick and hurt.
So, the plutonium files are all the papers and documents that tell the story of what happened with plutonium. It tells us how it was made, what it was used for, and what people did to it. These files help us understand what went wrong, so that we can make sure that it doesn't happen again in the future.
Scientists and experts study these files and work really hard to understand the dangers of plutonium and how to keep it safe so that people don't get hurt. The plutonium files are very important to make sure that we are safe, and so that we don't forget about the bad things that happened and make the same mistakes again.