The underground storage technology was developed by Holtec in the aftermath of 9/11. The storage system essentially consists of a 25 feet thick monolithic block of concrete with embedded thick walled metallic “cavity enclosure containers” fortified from above and below by thick reinforced concrete mats, making the storage system essentially indifferent to the height of the subterranean water table. Other beneficial attributes of HI-STORM UMAX are: (i) The system would shrug off any terrestrial earthquake recorded on earth without any risk of radiation release: Indeed, the licensing basis for the system's general certification bounds design basis earthquakes for all current U.S. nuclear plant sites; (ii) Situated deep below the ground, the stored MPC is firmly inaccessible to acts of terror or destructive eruptions of nature; (iii) Flood, fire, and other vagaries are likewise reduced to little more than operational nuisance. Wind, another bane of ventilated storage systems, has been marginalized into a second order effect using an artful design. “We are proud to be building a below-ground fortress for storing fuel at Callaway. Because the threat to nuclear installations is unlikely to diminish in the foreseeable future, we salute Ameren for their farsighted view in selecting HI-STORM UMAX for Callaway's on-site storage facility”, says Holtec's Director of Site Services, Steven Soler. Callaway’s underground storage site is preceded by a non-ventilated underground facility (for low heat loads) at PG&E's Humboldt Bay, installed and operating since 2007 (see photo). | 
