[en] The monitored retrievable storage (MRS) concepts considered are: metal cask (stationary and transportable); concrete cask (sealed storage cask); concrete cask-in-trench; field drywell; tunnel drywell; open cycle vault; closed cycle vault; and tunnel rack vault. These concepts were compared primarily upon the relative performance of the storage units on seven criteria which together encompass the key considerations for selecting an MRS concept, namely their ability to satisfy the MRS mission requirements. These criteria were: safety and licensing; environmental impacts; socioeconomic impacts; siting requirements; cost; concept maturity; and flexibility. Evaluations of the candidate concepts indicate that all of the concepts could satisfactorily serve in an MRS facility. However, using the above criteria, the two concepts selected for further design studies are the concrete cask (primary concept), better entitled the sealed storage cask, and the field drywell (alternate concept). It was recognized that the transportable metal storage cask may be used to supplement at-reactor storage until such time as the repository or MRS becomes available. Consequently, a hybrid storage facility may be required (e.g., one using concrete casks or field drywells, with the capability of receiving and storing the transportable cask). Both the concrete cask and the field drywell concepts can easily accommodate the transportable cask. Further design efforts will ensure the compatibility of the MRS designs with the transportable cask