Effects of slightly elevated temperatures on concrete materials and structures properties

Climate change is a global phenomenon and Canada’s national climate change assessments project the changes to continue. The rise in global temperatures due to climate change over the past several years has caused many utilities to see the operating temperatures of their nuclear power plants increasing, with some instances where the temperature limitations may have been reached or exceeded.<br>Temperature limitations for nuclear power reactors in North America are established in United States (US) and Canadian codes and standards (American Concrete Institute, 2013; ASME, 2023; CSA Group, 2019, 2025). Overall, temperature limitations are set to 65°C (150°F) over long-term periods, except for local areas (around penetrations for hot piping) where the temperature limit is 95°C (200°F) for the US codes, and 100°C (210°F) for the Canadian standards. Higher temperature limitations are set for short-term periods for the interior surface of the structures: 175°C (350°F) over large areas and 345°C (650°F) over local areas affected by impingements from steam or water jets.<br>Several studies have performed literature reviews focusing on the impact of elevated temperatures on a wide range of concrete properties (Acosta Urrea, 2018; Kassir et al., 1996; Mohammed, 2019; Naus, 2010). In addition, significant research has been conducted in the past several years to better characterize and understand the behaviour of concrete materials and structures when subjected to elevated temperatures. The objective of this paper is to synthetize the major findings of the various studies, with a focus on the properties relevant for nuclear power plant concrete structures when subjected to slightly elevated temperatures. To align with CNSC’s philosophy to ensure clarity on the regulatory requirements, the paper will also provide a regulatory perspective on how the CNSC expects that utilities would approach the impact of slightly elevated temperatures on nuclear concrete structures in the Canadian context. In particular, the paper will describe the type of technical information and analyses that would be required for CNSC staff to perform their regulatory oversight assessments of existing and new nuclear power plants.