Drawing the Line

Executive Summary

The Linear No-Threshold (LNT) model, which presumes that any dose of ionizing radiation carries a proportional risk of harm, has been the basis of radiation protection around the world for more than fifty years. This model underpins the regulatory frameworks of the U.S. Nuclear Regulatory Commission (NRC), the Department of Energy (DOE), and the Environmental Protection Agency (EPA). Amid a renewed push for deploying nuclear energy to meet rising global electricity demands, and following a Presidential Executive Order to evaluate radiation standards, a critical reassessment of these regulations is imperative.

This paper evaluates the scientific and policy landscape of radiation protection. While extensive research has expanded understanding of the effects of small radiation doses, significant uncertainty persists, particularly at doses below 100 mSv. Epidemiological studies in this range face significant limitations, as any potential increase in cancer risk is statistically indistinguishable from the normal background incidence of cancer and is confounded by a multitude of lifestyle and environmental factors. Consequently, the LNT model's assumption of a linear, proportional risk extending down to zero dose is not a proven scientific certainty but rather a conservative, simplifying assumption used for regulatory policy in the face of this ambiguity. The continued use of LNT is therefore not based on a fully validated scientific fact; it is a pragmatic, intentionally conservative policy choice. The paper argues that instead of an overhaul of the LNT model itself—a contentious change that would likely create greater disruption and still not achieve definitive scientific resolution—the focus should be on pragmatic policy and regulatory adjustments that leverage existing legal discretion.

Key Policy Recommendations:

Revising Risk Definitions: The NRC should define a quantitative threshold for "adequate protection," aligning its practice with the statutory risk standards established by Congress in the Clean Air Act. Furthermore, the principle of ALARA ("as low as reasonably achievable") should be reframed to focus on dose optimization rather than dose minimization, a change that aligns with international wording and discourages the expenditure of resources to reduce already negligible exposures.

Implementing a Tiered System for Dose Limits: A modernized, flexible system of dose and action limits is proposed:

• Tier 1 (Exempt or Clearance Limit): Establish a lower threshold of 1 mSv (100 mrem). Doses below this level, which are comparable to variations in natural background radiation, would be considered de minimis and exempt from ALARA and other regulatory requirements.
• Tier 2 (Public Dose Optimization): A public dose optimization threshold would be set at 10 mSv (1 rem). This matches the greatest variation in background exposure and then some moderate amount of anthropogenic exposure on top that can all be optimized but recognizes the impact of the many possible sources.
• Tier 3 (Occupational Action Limit): The occupational optimization threshold would be set at 20 mSv (2 rem), in line with DOE regulations and International Atomic Energy Agency recommendations. This could be further aligned with international standards to be 20 mSv (2 rem) averaged over a 5 year period.
• Tier 4 (Overall Dose Limit): Maintain the current occupational dose limit as 50 mSv (5 rem) and consider this joint public/occupational, with the action levels controlling to lower doses. This allows for safety based on current science, and for operational flexibility.

Recognition of Comparative Risks: Regulations must contextualize radiation risk by comparing it to the risks associated with other energy sources, such as pollution from fossil fuels, and other societal risks. Improved risk communication strategies are essential to address disproportionate public fear and accurately convey scientific evidence, thereby fostering greater acceptance of beneficial nuclear technologies.

These recommendations are designed to allow a prudent evolution of radiation protection standards. By adopting them, the U.S. can reduce unnecessary economic burdens, foster innovation in advanced reactor design, and improve the cost-competitiveness of nuclear energy, all while maintaining a world-leading safety record appropriate for workers and the public.