The nuclear safety profile of Southern California Edison’s twin unit San Onofre Nuclear Generating Station (SONGS) made a giant stride on August 7th when the 73rd and last multi-purpose canister (MPC) of spent nuclear fuel was placed in its designated below-grade storage vault.
The HI-STORM UMAX subterranean MPC storage system was selected by the Southern California Edison primarily because of its demonstrable indestructibility under any conceivable threat, including earthquake intensity levels exceeding those ever recorded. SONGS’ MPCs are further fortified for an extended service life by design and manufacturing measures such as the use of low-carbon stainless steel material, peened weld seams and Holtec’s proprietary low heat input welding process. Each MPC was dried using Holtec’s patented forced helium dehydration system, which is known to be uniquely effective in drying the used fuel especially the water-logged and damaged used fuel. The near-total radiation blockage ability of HI-STORM UMAX is another measure that further protects public health and safety and the environment.
To support the transfer of spent nuclear fuel from wet storage to dry storage, significant enhancements were developed and implemented for the SONGS project and are being utilized across the Holtec fleet. These enhancements include the development of an industry leading training program using a Systematic Approach to Training, detailed loading procedures with process improvements, and the development and utilization of camera systems and load monitoring equipment to make the loading of canisters into the HI-STORM UMAX storage modules even safer.
“Together with Holtec, we safely completed the largest spent fuel loading campaign in the United States. The below-grade UMAX system provides the safety and shielding to protect the public and the environment while the fuel is on site. The evaluation Southern California Edison performed prior to selecting the UMAX system was informed by SCE engineers and staff, industry experts and engagement with the community,” said Doug Bauder, SCE vice president of decommissioning and chief nuclear officer.
A robust aging management plan is being established for the SONGS storage system to ensure that any degradation would be identified long before it would become an issue. The MPCs in the HI-STORM UMAX are licensed for transport and are ready to be shipped if and when a consolidated interim storage facility (CISF) becomes available. Removing the storage canisters away from the corrosive salt-air environment like SONGS to a more conducive environment is possible because Holtec is working to establish the HI-STORE CISF in the dry and arid land (a more hospitable environment for the MPCs) in southeastern New Mexico. The HI-STORE CISF also employs the same subterranean storage system as used at SONGS and shares its robust structure and vanishingly small radiation dose to the public and environment. Subject to the continuing support of the host communities and appropriate regulatory approval, we expect to deliver the HI-STORE CISF to the U.S. industry, which will provide an environmentally superior alternative to the on-site storage in the aggressive environment at the coastal sites around the country. Removal of spent nuclear fuel to HI-STORE CISF from shuttered nuclear plants, like SONGS, allows the full site to be returned to more productive use.
Holtec is working with Ukraine’s national nuclear company, Energoatom, to establish a similar CISF in the north of the country to serve that country’s VVER nuclear units. That facility is expected to be operational early next year.