After spent nuclear fuel (SNF) has cooled (thermally and radioactively) for approximately 5 years in a wet fuel pool at a nuclear reactor, it can be transferred to dry cask storage.  Almost all of the nuclear power plant sites located in the U.S. are either currently using or anticipating the use of dry casks for the storage of SNF.  Dry cask storage takes several forms in the U.S., but generally a dry cask consists of a fuel storage grid placed inside a steel inner container (approximately 1/2 inch to 5/8 inch thick), which is then placed inside a concrete outer cask (typically between 2.5 and 3 feet thick).  The entire system weighs between 160 and 180 tons (320,000 to 360,000 pounds) and is located in an open air environment on a large concrete storage pad, which is typically referred to as an independent spent fuel storage installation (ISFSI).  The SNF located inside the cask is surrounded by an inert gas and the canister is welded or bolted closed, but the steel canister inside the concrete cask is cooled by natural circulation of air.  Currently, about 1/4 of the SNF in the U.S. is stored in dry casks, although the amount and percentage of the total will grow over the next several decades.

An excellent video of the process utilized at the now decommissioned Yankee Rowe Nuclear Power Station reviews the process associated with transferring SNF from wet fuel pools to dry storage casks.

Yankee Rowe SNF Storage — Fuel Pool to Dry Cask Video

There are four vendors supplying dry casks systems to nuclear power plant powers in the US:  BNFL Fuel Solutions; Holtec; NAC International; and Transnuclear.  Information regarding actual and specific costs for dry cask storage systems are proprietary and not available publicly.  However, it has been estimated that the cost to install an ISFSI at a two-unit nuclear power plant site is approximately $20 and $30 million.  The estimate cost per cask is between $1 and $2 million but the attendant expense to load drives the cost to between $7 and $10 million.  The operational costs of the ISFSI at an operating nuclear power plant site is about $1 million per year, but this cost increases to between $4.5 and $8 million per year at nuclear power plant sites that are already shutdown.