Which radioactive isotopes would those be? I would bet you have no idea.

Comments like this show that people do not understand how radioactive decay works. Isotopes with short half lives are highly radioactive but, because we are talking about isotopes with short half lives, they decay away quickly. Isotopes with long half lives are not very radioactive. We use long half life isotopes like uranium to shield people from the radiation of other isotopes.

There's also the matter of not all radiation being equal. The types of emissions include alpha, beta, gamma, neutrons, and some more exotic kinds. Gamma is the really hard to contain type. Neutrons are a bit of a problem too. Alpha and beta emitters are far from harmless, you don't want to use this stuff to season your salad, but putting these isotopes in a steel drum until it all decays away is a perfectly cromulent way to deal with them.

The most dangerous isotopes from nuclear fission have half lives somewhere around 30 years, specifically strontium-90 and cesium-137. These isotopes are biologically active and so are taken up quickly by plants and animals, and tend to accumulate in the food chain. Once in the body it can decay and do considerable damage, but since most of the radiation from these elements is beta decay it can be contained in a simple steel drum. Not for thousands of years but for an estimated 300 years. 300 years is about 10 half lives, the atoms decayed down to 1/1000 of it's original number. That means one tonne of the stuff decays down to one kilogram, or one kilogram becomes just a gram. 300 years is a long time, but it's also not "thousands" of years. Humans have been building structures that last more than 300 years for quite some time, we can do that again today and with much greater ease than 1000 years ago.

Most fission products have very short half lives, they decay away in a few years. Spent fuel rods are stored at nuclear power plants for a few years in cooling pools to allow these to decay away. The water not only keeps the fuel cool but it is a very effective shield against all types of radiation. The worst stuff takes 300 years to decay away to levels of little concern. The really long lived stuff, like plutonium, is not a radiation hazard. There's a lot of concern about containing plutonium just not because it is radioactive. There is so much concern about it because it is a valuable fuel. Like any fuel it can be burned slowly to power machines or burned quickly to make weapons. A truck loaded with fuel oil can heat an office building all winter, or level it in seconds. The plutonium from spent fuel is worthless for weapons because it contains isotopes that are far too willing to spontaneously fission. A weapon core made from reactor grade plutonium could detonate prematurely, which I would imagine is quite undesirable. A more likely outcome is it gets real hot from the fission and melts, destroying any weapon it may be in and irradiating anyone around it with potentially lethal doses of neutrons. We call it "reactor grade" because it's the kind that comes out of reactors and also the kind that goes into reactors for fuel. We can reprocess this into fuel, potentially creating a breeder cycle of turning depleted uranium and thorium into fuel.

Spent fuel from nuclear power does not need to be contained for thousands of years, it becomes quite inert in a matter of centuries at most, perhaps suitable for reprocessing in only decades. The logging industry deals with production cycles on the order of decades. The airline industry plans for keeping the same model of airplanes flying for decades. The waste products from nuclear power is manageable, and has been managed for decades already. This is a solved problem, the only thing that held these solutions up for the last 50 years have been Democrats and the Democrats had a change of heart last summer.