Spent Fuel Pools and Decommissioning
In July 2020, workers removed the last of the spent nuclear fuel assemblies from the Unit 3 pool at SONGS and placed them into a stainless-steel canister that was then welded shut. That canister then began a slow and steady journey to the UMAX dry fuel storage system where, on August 7, it became the last of 73 canisters now stored there.
Shortly after all the fuel was placed in dry storage, an amended Nuclear Regulatory Commission license for SONGS went into effect. This amended license prevents Southern California Edison from returning any spent fuel to the Unit 2 or Unit 3 pools and with good reason. Retaining the spent fuel pools is inconsistent with the goal of decommissioning the SONGS facilities and— despite what some have contended — is not necessary. In the unlikely event a fuel canister ever needs repair or repackaging, other methods are available that are preferable to indefinitely leaving the nuclear plant standing in order to maintain the spent fuel pools.Eventually, the water in the pools will be processed and released through a conduit more than one mile off-shore. When it is released, it will meet all regulatory requirements for safety. Following that, the spent fuel pool buildings at SONGS will be dismantled as part of the ongoing deconstruction of the site.
A Little History
To date, all decommissioned commercial nuclear plants that continue to store fuel onsite have removed their spent fuel pools. These plants include Rancho Seco Nuclear Generating Station (California), Humboldt Bay Nuclear Power Plant (California), Connecticut Yankee Nuclear Power Plant (Connecticut), Yankee Rowe Nuclear Power Station (Massachusetts), Maine Yankee Nuclear Power Plant (Maine), Big Rock Point Nuclear Power Plant (Michigan), and Trojan Nuclear Power Plant (Oregon). There are others, as well.
The NRC has expressly considered the issue and has decided that a spent fuel pool is not necessary or required once spent fuel is placed in dry storage. As an indication of its policy in this regard, this NRC webpage provides information to the public on the decommissioning of nuclear power plants, including a high-level discussion of the activities necessary for decommissioning. It makes no reference to any required continued operation of a spent fuel pool.Returning a spent nuclear fuel canister to the pool for any reason is simply unnecessary, so there is no need to maintain a spent fuel pool. The canisters are seal-welded shut, leak tested prior to placement in storage, and are extremely robust 50-ton behemoths. Since 1986, these types of canisters (the kind also used at SONGS since 2003) have performed extremely well, with a zero failure rate. In the U.S., 93% of the spent fuel storage systems in place are these welded-lid, stainless-steel canisters. The canisters can perform their safety functions for 100 years or more.
SCE is Doing More
When the California Coastal Commission made its decision to approve the coastal development permit to safely dismantle SONGS, it directed SCE to submit a spent fuel Inspection and Maintenance Program (IMP) prior to the removal of the spent fuel pools.
In the unlikely event canister repairs are ever needed, the IMP includes an in-situ repair method that does not require retention of the pools. The repair method involves using robots that can deliver a metallic coating that bonds to the canister surface. The process is also used for military applications, including on U.S. Air Force aircraft. The U.S. Navy uses the process for submarine repair. The Coastal Commission had the plan reviewed by an independent engineering firm which found it satisfactory.
The Commission unanimously approved SCE’s IMP in July 2020. Although there are other methods that could also be employed without resorting to maintaining the spent fuel pools, this is the chosen canister repair method SCE would employ in the event a repair was ever necessary.
The Job at Hand
There are practical reasons why retaining a spent fuel pool would not be feasible at SONGS. Operation of the SONGS spent fuel pools relies on infrastructure that is interconnected with other plant buildings and structures, systems and components (SSCs), including power supply systems; heating, ventilation, cooling and lighting systems; radiation monitoring equipment; communications equipment; and a command center. In order for the pools to remain functional and in compliance with NRC licenses and NRC regulations for even the temporary storage of fuel, either: a) some or all of those components would have to be retained (meaning a number of adjacent buildings and components, would have to remain); or b) it would be necessary to seismically analyze, license, design, procure, and install new SSCs to replace the removed SSCs.
Either way, a substantial amount of infrastructure that otherwise would be removed as part of the dismantlement project would be left in place at SONGS. This result would be contrary to several of the decommissioning objectives, the prompt completion of radiological decontamination and prudent use of customer funds being two important ones.
In addition, because the spent fuel pool buildings are located in the heart of the plant in an area that is central to dismantlement work, it would pose significant challenges to the performance of decontamination and dismantlement work in that area should the decommissioning contractor have to cautiously avoid operational pools. For all these reasons, if SCE were required to maintain a spent fuel pool, it would no longer be feasible to further dismantle the site.
The Bottom Line
Current and developing technology provides options for addressing potential canister damage/degradation. Rather than transferring a canister to a spent fuel pool, the corrective actions would more likely include assessment and continued inspection, in-place repair, or creating a secondary confinement boundary for the spent fuel (e.g., nesting a canister within another container).
SCE maintains a shared interest with the local communities to move forward with dismantling the plant in a safe and timely manner and restoring the SONGS site for return to the U.S. Navy.
(Posted May 27, 2021)