Holtec International has been manufacturing dry casks for the storage of SNF from both PWRs and BWRs since 1991.  Holtec manufactures the Hi-Storm cask system, which is a vertically-oriented multi-purpose canister (MPC) that is available in several sizes:  the MPC-24 for storage of 24 fuel assemblies from a PWR; the MPC-32 for storage of 32 fuel assemblies from a PWR; and the MPC-68 for storage of 68 fuel assemblies from a BWR.  As of the end of 2009, 316 MPCs manufactured by Holtec were being used by 18 nuclear power plants in the US to store SNF.