NUHOMS® HSM MATRIX for Centralized Interim Storage of a variety of Spent Fuel Canisters

In the United States, used fuel assemblies discharged from nuclear power plants (NPPs) have historically been stored on-site using licensed dry storage systems. Due to shutdown/decommissioning of several NPPs and delays in the implementation of the geological repository, there is a need to develop solutions to manage the storage of dry storage systems in interim storage facilities. The Centralized Interim Storage Facility (CISF) functions as an intermediate repository / staging area for dry storage systems for an extended duration of time prior to eventual transportation to a geological repository. The operation of a CISF will lead to a significant reduction in the number of Independent Spent Fuel Storage Installations (ISFSIs) nationally and enable release of space in those decommissioned reactor sites that currently only maintain their respective ISFSIs. The NUHOMS® System has been licensed in the United States for the on-site storage of used nuclear fuel for more than 35 years. The system consists of a dry shielded canister (DSC) containing the used nuclear fuel which is inserted into the concrete horizontal storage module (HSM) using a transfer cask (TC). Several DSCs designs have been licensed for storage and are characterized by differences in physical dimensions (diameter, length), allowable used fuel contents (BWR, PWR), performance parameters (heat load, burnup). The NUHOMS® MATRIX is an evolutionary design of the storage module that will provide for a two-tiered placement of DSCs resulting in improved storage efficiency, stability and self-shielding. The design of the MATRIX ensures that it is able to house the various DSC designs and therefore, serve as a universal over-pack. The consideration of a universal over-pack offers several advantages for the CISF leading to simplification in design, operations and aging management program implementation. This paper provides additional insights into design and licensing of the MATRIX in a CISF with an objective to be employed as a universal storage over-pack for various DSC types. This paper also discusses the current efforts being undertaken to enhance the design of the MATRIX HSM for this purpose.