Since 1986, more and more fuel storage pools have approached their maximum holding capacity (Figure 4). By 2017, all but one site (which was constructed with sufficient pool storage capacity to accommodate all of the spent fuel produced during the reactor’s lifetime) will be at capacity, necessitating the greater use of dry storage.
and more here: http://www.nae.edu/Publication...
On site storage is not a viable or better long term solution. We are only now hitting a point where reactors are starting to be retired. Do you think that the utility companies running them will have the same committment to the storage 10, 50, 250 years later? The same can be said about security. Even regionalizing above ground storage poses risks and certainly increases the political drama
As another poster notes, some of it could be reprocessed for further use but ultimately there is waste to deal with. And it is true that MOX does not itself pose any terrorist type risk, the risk comes from having too many reprocessing locations where materials can be "lost". Done properly reprocessing could buy some time to deal with the longer term needs.