There's different types of plutonium that's made. Bombs are made from Pu-239. But reactors will normally produce Pu-240 as well, unless you specifically design your reactor and fuel it appropriately to produce mostly Pu-239.

So what's the difference? Pu-240 is hot. It's too radioactive to make bombs out of, because you'll end up cooking your workers. And because it's so similar in weight to Pu-239, you can't effectively separate it out.