“Advanced” Isn’t Always Better

The report argues that most non-light-water reactors (NLWRs) do not provide significant enough improvements over light-water reactors (LWRs) to justify their associated safety, security, and proliferation risks. It specifically evaluates sodium-cooled fast reactors (SFRs), high-temperature gas-cooled reactors (HTGRs), and molten salt reactors (MSRs), finding that claims regarding 'burning' nuclear waste are oversimplified and that the timelines for commercialization are often unrealistic. The author recommends that the US Department of Energy (DOE) prioritize improving existing LWR technology over pursuing immature NLWR designs.

• Most non-light-water reactors (NLWRs) currently under consideration do not provide improvements over light-water reactors (LWRs) significant enough to justify their risks, costs, and development time.
• Sodium-cooled fast reactors (SFRs) possess inherent safety instabilities, specifically a positive void coefficient, which can lead to rapid power increases and potential core damage if coolant boils.
• High-temperature gas-cooled reactors (HTGRs) rely on TRISO fuel for safety, but this fuel is not meltdown-proof and can release fission products if temperatures exceed 1,600°C.
• Molten salt reactors (MSRs) present unique safety risks, including the continuous release of gaseous fission products like xenon-137, which decays into environmentally hazardous cesium-137.
• The claim that NLWRs can 'burn' or 'consume' nuclear waste is a misleading oversimplification, as it requires costly and proliferation-risky chemical reprocessing.
• High-assay low-enriched uranium (HALEU), required by many NLWR designs, poses higher proliferation and terrorism risks than the low-enriched uranium (LEU) used in LWRs.
• Commercialization timelines for NLWRs are often unrealistic; the DOE's goal of 2027 for some designs may bypass critical prototype testing stages necessary for safety.
• Reprocessing and recycling fuel cycles, often proposed for NLWR sustainability, significantly increase the risk of nuclear proliferation and terrorism by separating weapon-usable materials.
• Breed-and-burn reactors could theoretically increase uranium efficiency without reprocessing, but they face immense technical hurdles, including the need for ultra-high burnup fuels.
• The US Department of Energy's (DOE) pyroprocessing efforts at the Idaho National Laboratory have been largely unsuccessful, processing only about 20% of the target spent fuel over two decades.

APA

Lyman, E. (2021). “Advanced” Isn’t Always Better. Union of Concerned Scientists. https://www.ucs.org/sites/default/files/2021-05/ucs-rpt-AR-3.21-web_Mayrev.pdf

Chicago

Lyman, Edwin. “Advanced” Isn’t Always Better. Union of Concerned Scientists, 2021. https://www.ucs.org/sites/default/files/2021-05/ucs-rpt-AR-3.21-web_Mayrev.pdf.

Wikipedia

{{cite report |last1=Lyman |first1=Edwin |title=“Advanced” Isn’t Always Better |publisher=Union of Concerned Scientists |date=March 2021 |url=https://www.ucs.org/sites/default/files/2021-05/ucs-rpt-AR-3.21-web_Mayrev.pdf |access-date=23 October 2026 |via=Climate Insights Directory}}

BibTeX

@techreport{lyman2021advanced, author = {Lyman, Edwin}, title = {{“Advanced” Isn’t Always Better}}, institution = {Union of Concerned Scientists}, year = {2021}, month = mar, url = {https://www.ucs.org/sites/default/files/2021-05/ucs-rpt-AR-3.21-web_Mayrev.pdf}, urldate = {2026-10-23}, note = {Indexed by Climate Insights Directory} }