Assessing the Safety, Security, and Environmental Impacts of Non-Light-Water Nuclear Reactors

The Union of Concerned Scientists concludes that most non-light-water reactor (NLWR) designs do not offer sufficient improvements over light-water reactors (LWRs) to justify their increased safety and proliferation risks. The report argues that NLWRs, including sodium-cooled fast reactors, high-temperature gas-cooled reactors, and molten salt-fueled reactors, are technologically immature and unlikely to be commercialized in time to significantly impact the climate crisis. It recommends that the US Department of Energy suspend the Advanced Reactor Demonstration Program until the Nuclear Regulatory Commission determines if full-scale prototype testing is required for safety validation.

• Most non-light-water reactor (NLWR) designs fail to provide improvements over light-water reactors (LWRs) that are significant enough to justify their associated risks.
• Sodium-cooled fast reactors (SFRs) possess critical safety flaws, including the potential for runaway power excursions due to a positive void coefficient and the risk of the core exploding under severe accident conditions.
• High-temperature gas-cooled reactors (HTGRs) rely on TRISO fuel, which is not meltdown-proof and can release fission products if temperatures exceed 1,600ºC.
• Molten salt-fueled reactors (MSRs) present unique safety and security risks, including highly corrosive liquid fuel and the routine release of gaseous fission products that could interfere with global nuclear test ban monitoring.
• The use of high-assay low enriched uranium (HALEU), required by many NLWRs, increases nuclear proliferation and terrorism risks compared to the low-enriched uranium (LEU) used in LWRs.
• Claims that NLWRs can be commercialized by the late 2020s are unrealistic because they would require bypassing critical prototype and performance demonstration stages.
• The claim that nuclear reactors can 'burn' or 'consume' nuclear waste is an oversimplification, as it requires chemical reprocessing that increases the risk of plutonium diversion and theft.

APA

Union of Concerned Scientists (2021). Assessing the Safety, Security, and Environmental Impacts of Non-Light-Water Nuclear Reactors. https://www.ucsusa.org/sites/default/files/2021-03/advanced-reactors-es.pdf

Chicago

Union of Concerned Scientists. Assessing the Safety, Security, and Environmental Impacts of Non-Light-Water Nuclear Reactors. 2021. https://www.ucsusa.org/sites/default/files/2021-03/advanced-reactors-es.pdf.

Wikipedia

{{cite report |author=Union of Concerned Scientists |title=Assessing the Safety, Security, and Environmental Impacts of Non-Light-Water Nuclear Reactors |date=March 2021 |url=https://www.ucsusa.org/sites/default/files/2021-03/advanced-reactors-es.pdf |access-date=23 October 2026 |via=Climate Insights Directory}}

BibTeX

@techreport{unionofconcernedscientists2021assessing, author = {{Union of Concerned Scientists}}, title = {{Assessing the Safety, Security, and Environmental Impacts of Non-Light-Water Nuclear Reactors}}, institution = {Union of Concerned Scientists}, year = {2021}, month = mar, url = {https://www.ucsusa.org/sites/default/files/2021-03/advanced-reactors-es.pdf}, urldate = {2026-10-23}, note = {Indexed by Climate Insights Directory} }