Ste-W

Hope this is the correct discussion to post this, I simply cannot get my head around the basic theory surrounding Atomic Radiation. I have been working near an old Nuclear Power Station in Wales, its manily de-commissioned now but radioactive waste is still insitu, and the Station will not be totally safe until 2083 apparently. MY difficulty is actually understanding how that waste , wether it be spent fuel or simple pipe fittings from the reactor buidling remains so powerfully iradiated for so long. Where did such radiactive material come from in the first place.