About the Tool

Use NSI’s Reactor Selection Tool to explore reactor designs

NSI’s Reactor Selection Tool (RST) is an interactive and accessible resource that enables informed comparisons of different reactor designs on key scaling criteria. It is the product of open-source data, expert analysis, and informed opinion. The RST does not endorse reactors; it is designed to guide utilities, offtakers, investors, governments, and other decision-makers across the global nuclear energy landscape through a complex marketplace to find the design that best suits their needs.

Reactor Scope

The RST includes a set of 35 reactor designs from around the world that range in size, technology, and deployment application. The RST’s broad scope allows users to, for example, compare small reactors with large reactors or compare reactors that are operating today with reactors that have not been built yet.

Measurement Framework

An international panel of experts helped develop the measurement framework that each reactor is evaluated against. The result of that consultative process is eight overarching criteria (each composed of at least two indicators), which are essential for efficient and responsible nuclear energy scaling:

Each reactor receives a composite score on each criterion based on a weighted additive formula of its indicators (rounded to the nearest whole number). The RST’s indicator weights are based on feedback from the international panel of experts and NSI analysis on what factors are most consequential. These weights are subjective and could vary based on the importance each end-user places on aspects of reactor design.

Some indicators are represented across multiple criteria because they are relevant to the assessment of multiple aspects of the design. Because the RST does not provide a cumulative score that combines criterion scores, no indicators are double counted. All scores are accompanied by qualitative summaries that provide additional context.

Data Collection

The RST is based exclusively on publicly available information. NSI engaged reactor vendors for feedback at multiple points throughout the evaluation process, by inviting them to self-assess their reactor(s) before NSI’s scoring began and react to NSI’s scoring upon its completion. Participation in this process was voluntary, and not all vendors chose to do so. NSI only incorporated vendor feedback that could be substantiated by public sources and aligned with the tool’s methodology. A reactor’s inclusion in the tool does not indicate the vendor’s approval or agreement with the scores.

For reactors in the tool that have not been deployed yet, NSI derived scores from general design parameters. The wide range in design maturity and reliance on publicly available information drove the decision to use an ordinal (1-5) rating scale for the criteria.

Limitations

The RST evaluates reactors only on technology-specific criteria; it does not incorporate deployment-specific factors. Although deployment-specific factors are essential to the reactor selection process, this tool is not designed to accurately measure them.

Attempting to capture the range of scenarios in which a reactor could be built not only is beyond the scope of the tool but also would undercut its central purpose: enabling decision-makers to compare reactors based on their specific needs.

Learn more about deployment-specific factors that NSI recommends decision-makers consider.

Updates

NSI recognizes that the reactor landscape will evolve over time and will update the scope of reactors included and their scores on a periodic basis to capture those changes. The current scores reflect information available to NSI as of March 4, 2026. The scores do not reflect a definitive assessment of reactor capabilities.

Glossary of Acronyms

BWR: Boiling water reactor
GW: Gigawatt
GWe: Gigawatt electrical
HALEU: High-assay low-enriched uranium
HTGR: High-temperature gas-cooled reactor
HWR: Heavy water reactor
IAEA: International Atomic Energy Agency
LEU: Low-enriched uranium
LEU UO2: Low-enriched uranium dioxide
LWR: Light water reactor
MPa: Megapascal
MSR: Molten salt reactor
MW: Megawatt
MWe: Megawatt electrical
MWe-year: Megawatt electrical year
MWh: Megawatt hour
MWt: Megawatts thermal
NRC: Nuclear Regulatory Commission
PWR: Pressurized water reactor
SFR: Sodium-cooled fast reactor
SMR: Small modular reactor
TRISO: Tristructural isotropic