An independent spent fuel storage installation (ISFSI) is a place to safely store spent nuclear fuel while it is waiting for a geological repository to permanently dispose of the material. The amount of nuclear fuel required to supply a typical American citizen with a lifetime of energy would fill a single soda can with waste. This means that for a large power plant, it won't generate very much spent fuel at all for the amount of energy it produces. Still, this spent fuel must be handled safely and that over the long term.
One way this country has found to do that on the short term is through allowing the construction and use of an ISFSI. Most nuclear power plants have a small one on site or will be constructing a small one on site to safely store the spent fuel until a geological repository can be licensed. The reason a geological repository is needed is so that we can have a solution which was agreed upon and recommended by the experts in the nuclear field. That solution being a federally licensed geological repository.
The benefit of requiring such a license is that this means the federal government will provide all the technical oversight and reviews to verify that the facility would meet all the safety requirements called out through many consensus based technical standards and similar criteria.
Right now, a licensed geological repository for spent fuel does not exist. The Yucca Mountain facility in southern Nevada is intended to eventually meet these requirements to receive the spent fuel but the process for it obtaining a license is perhaps tenuous at best. Some feel it will eventually occur although anti nuclear activists are generally against it.
Without a licensed geological repository, there are spent fuel storage casks which can hold the material for many decades without meaningful degradation. These storage casks are typically large reinforced concrete cylindrical bunker like canisters which are designed to safely hold the fuel for long periods of time. The locations designed to hold these storage casks are ISFSI's which are not meant to be a permanent solution to the spent fuel.
A more comprehensive solution has been determined through consensus of many experts in the field that a single large scaled ISFSI is more appropriate to handling the temporary storage of these spent fuel casks. In this way, a single security force, facility design and operations crew can easily handle all the casks from the fleet of reactors around the country. A single large reactor will typically generate less than a dozen or so of these casks over its lifetime and focusing a robust security and control plan into one design has been considered to be the best overall solution. This allows improvements in safety, cost and efficiency in general.
The Eddy-Lea energy alliance has been trying to obtain funding to license and build such a facility in southeast New Mexico but has met limited success. Similarly, Waste Control Specialists in Andrews County Texas is also seeking to obtain this scope of work from the nuclear industry. If Waste Control Specialists (which is actually much closer to Eunice, NM than to Andrews, TX) is able to do this, it will be a very welcome improvement to the nuclear industry.