Palisades SMR, LLC, a wholly-owned subsidiary of Holtec International, submitted the first part of a phased construction permit application for the dual-unit SMR-300 plant – Pioneer units 1 and 2 – to the US Nuclear Regulatory Commission (NRC) in December. This included a limited work authorisation (LWA) request. An LWA allows certain construction activities to commence before a construction permit or combined construction and operating licence has been issued. The NRC accepted it for review and docketed it in February.
The exemption granted by the NRC on 28 August authorises installation of permanent support-of-excavation (SOE) and cutoff-wall systems for Pioneer units 1 and 2. These systems include diaphragm walls, soldier-pile soil-mix walls, and perimeter cutoff walls, with tiebacks or struts as needed, Holtec said. These early works will establish the stable excavation and foundation conditions needed to support and accelerate subsequent plant construction following LWA approval. The SOE walls will eventually be “retired in place”, with the space between the walls and permanent structures backfilled to grade, it added.
Ahead of issuing the exemption, the NRC issued an Environmental Assessment and Finding of No Significant Impact for the authorised activities concluding that the granting of the exemption would not have any detrimental effects on the quality of the environment. The regulator determined that installation and retirement of the SOE walls would not adversely affect the safe design or siting of Pioneer units 1 and 2.
Holtec will perform geologic mapping and data collection during excavation, notify the NRC when the excavation is open for inspection, and account for the retired SOE walls in soil-structure interaction analyses.
The SMR-300 is a pressurised water reactor producing about 300 MW of electrical power or 1050 MW of thermal power for process applications.
“The approval reflects Holtec’s disciplined, risk-informed approach to advancing the Palisades project and marks another step toward deploying 680 megawatts of clean, reliable energy through Pioneer Units 1 and 2,” the company said.
The Palisades site is also home to a single-unit 805 MWe pressurised water reactor, which closed in 2022 and Holtec is now in the process of bringing back into service.
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An illustrative view of the permanent SOE system (Image: Holtec)
