Holtec International Storage Module
The HI-STORM 100 System is designed to accommodate a wide variety of spent nuclear fuel assemblies and other radioactive materials in a single overpack by utilizing different MPCs.
The HI-STORM 100 System utilizes the HI-TRAC Transfer Cask for transporting the MPC from the spent fuel pool and for inter-cask MPC transfer required for on-site storage and off-site transport.
The HI-STORM 100 is a vertical, ventilated, cylindrical overpack engineered to minimize the local area dose and to provide a robust structural enclosure for the MPC situated inside it. Specifically, HI-STORM 100 is designed to easily withstand high-velocity winds, tornadoes, high energy lightning, and other natural phenomena.
The HI-STORM system is available in two configurations; above ground & underground.
Above-Ground HI-STORM Module
In practically every region of the world above-ground HI-STORM can be deployed in a free-standing configuration, although the design readily lends to anchoring it to an ISFSI pad. The anchored configuration has been licensed by the NRC under general certification.
The above-ground HI-STORM overpack is a METCON (metal/concrete), heavy-walled cylindrical vessel that consists of inner and outer cylindrical steel shells. These members enclose a thick concrete wall that is installed following assembly of these components. It has a heavy bolted concrete and steel lid.
The internal cavity of the above-ground HI-STORM is of sufficient height and diameter to contain the MPC. The cask provides the biological shielding necessary to protect the public and the structural strength necessary to protect the cask’s contents against natural phenomena such as tornado wind loading and any wind-driven missile events.
The above-ground HI-STORM has four air inlets and four air outlets located at the lower and upper ends of the cask ducts to permit passive cooling of the contained MPC by natural convection. The ducts are equipped with duct photon attenuators which are a Holtec innovation that choke off gamma streaming. A fine mesh screen protects against insect ingress. Some attributes of above-ground HI-STORM model which render it an optimal SNF storage device are:
- The structural backbone of the HI-STORM 100 overpack, which is made of high-ductility carbon steel, is qualified to meet ASME Section III Subsection NF.
- The steel weldment encasing the concrete provides the structural function. Therefore, the potential for loss of the structural strength from potential weather-induced degradation of concrete is eliminated.
- Inlet and outlet duct geometries and the (patented) Photon Attenuator device eliminate radiation streaming.
- The inside surface is equipped with design features to minimize inertia loads on the MPC under a postulated tip-over event.
- The annular space between the overpack and the MPC is sized to maximize the ventilation induced cooling of the MPC (and contained SNF).
- The engineered seismic dissonance features incorporated in the HI-STORM 100 System helps stabilize the HI-STORM 100 System at high seismic ISFSIs.