Let me help you with that. Jacques is correct in his description of activity. I just checked my radiation detection text book to make sure (that would be embarrassing wouldn't it!)
However, "lethal" is a bit of an ambiguous term when applied to the waste from the nuclear power generation. After cooling down, the fuel assemblies will most certainly be emitting ionizing radiation that will be detectable for hundreds of thousands of years, as you suggest. This does NOT mean it is "lethal" for this time period. UNLESS you open one of the assemblies and make an industrial waste smoothie. Most of the long lived isotopes contained in the assembly will be deadly as heavy metals. So there is still danger, but it is easily manageable, just like the waste from many other industrial processes (like making solar panels, or batteries for hybrids for instance).
However, "lethal" is a bit of an ambiguous term when applied to the waste from the nuclear power generation. After cooling down, the fuel assemblies will most certainly be emitting ionizing radiation that will be detectable for hundreds of thousands of years, as you suggest. This does NOT mean it is "lethal" for this time period. UNLESS you open one of the assemblies and make an industrial waste smoothie. Most of the long lived isotopes contained in the assembly will be deadly as heavy metals. So there is still danger, but it is easily manageable, just like the waste from many other industrial processes (like making solar panels, or batteries for hybrids for instance).