The aim to keep radiation doses from the nuclear industry as low as reasonably achievable (ALARA) is enshrined in the fundamental principles of the International Commission on Radiation Protection (ICRP). US President Donald Trump raised eyebrows when his Executive Order on reforming the US Nuclear Regulatory Commission (USNRC) called for reliance on this principle to be revisited. But a new UK Nuclear Regulatory Review (NRR) produced for the Department for Energy Security and Net Zero (DESNZ), which provides advice to government on how to reduce regulatory barriers to fast deployment of nuclear power, has also called the principle into question – at least in its practical application. Is this fundamental principle under threat?
When President Trump tasked the USNRC with revisiting its approach to radiation safety, he including reconsidering its reliance on the linear no-threshold (LNT) model and the ALARA principle. Instead, the NRC is directed to explore the adoption of “determinate, data-driven radiation limits” in consultation with the Department of Defense and Department of Energy, and the Environmental Protection Agency (EPA).
LNT is a fundamental of the ICRP’s system, adopted in the International Atomic Energy Agency’s (IAEA’s) regulations. It assumes that any amount of ionising radiation carries some risk of causing harm (typically cancer) and the risk increases linearly with dose. The NRR says that the reality of radiation exposure is more complex, and some critics say the LNT model over-estimates the risks at low doses or argue that there is a threshold for harm.
The NRR notes that the ICRP itself states that the LNT model carries “uncertainty on health effects at low doses”, underscoring the need for a proportionate approach with cautious application at very low doses. But the broader international radiological protection community, including the ICRP and the UK, continue to support its use as the best available tool for public health policy and radiation protection.
The argument over the role of the LNT model is a longstanding one. It was revisited recently in a paper (Reevaluation of Radiation Protection Standards for Workers and the Public Based on Current Scientific Evidence) published by Idaho National Laboratory in July 2025 with the support of the US DOE. Lead author Dr John C Wagner is the director of INL and president of Battelle Energy Alliance.
Wagner and his co-authors say, “the preponderance of available evidence suggests that current radiation protection frameworks may be overly conservative”. They say studies do not show statistically significant adverse health effects at doses below 10,000 mrem delivered at low dose rates and this is born out by studies of populations where natural background radiation is high. They add, “Multiple major professional organizations acknowledge significant limitations and uncertainties” in LNT.
The INL paper supports a numerical exposure limit. The authors suggest maintaining an annual occupational whole-body dose limit of 5,000 mrem/yr, as currently applies, and eliminating all ALARA requirements and limits below this threshold. They suggest future consideration of a higher limit, 10,000 mrem/yr, which “may maintain sufficient safety margins while further reducing protection costs”.
The INL concern is over the elements of a “multifaceted system” that solidifies the outcomes of ALARA. Regulatory guides include recommendations for optimising facility layout and equipment design, remote-handling, ventilation systems, reducing source terms, decontamination and radiation monitoring. They say, “Collectively, this regulatory framework transforms ALARA from a philosophical aspiration into a binding legal requirement. Licensees must reduce doses below the 5,000 mrem limit regardless of economic impact because ALARA implementation is an explicit regulatory obligation rather than simply a goal or ideal.”
They say that this is “overly effective” because it results in doses “well below the regulatory limit” – 58 per cent of monitored individuals at commercial light-water reactors in Calendar Year 2022 were below any measurable dose.
The UK’s NRR also had concerns over the application of ALARA . It says, “The focus by dutyholders and regulators has increasingly been on the ‘as low as’ and less on the ‘reasonably practicable’ parts of the ALARP principle, and a culture of over-conservatism and risk aversion has become entrenched. This has resulted in a slow overall decision-making environment where innovative choices are discouraged.”
Both the INL paper and the NNR argue that the ALARA principle has had the effect of stepping up measures until they are far beyond the ‘reasonable’ definition.
The UK’s ALARA principle is also expressed as being ‘as low as reasonably practicable’ (ALARP). Rather than focusing on the dose itself, the UK authors’ concern was the tendency to go on reducing doses far past what was practicable, given the cost. They say the application of ALARP has become “overly stringent” and “It sometimes functions as a ratchet that demands ever-lower risk levels and radiation exposures, even when the benefits are negligible or the costs disproportionate.”
This is in part due to a lack of clear direction on the tolerability of risk and in the assessment of proportionality. The nuclear sector “frequently neglects to consider a portfolio view of risk” in applying ALARP, which drives local risk reduction without accounting for strategic factors, and the risks associated with inaction and poor programme delivery.
The report said this was a government responsibility. It should define the Tolerability of Risk for the nuclear sector with regard to the modern state of the nuclear sector, and the societal demand for its outputs across energy, decommissioning and defence. This should be clearly communicated and periodically reviewed. Risks at or below broadly acceptable levels should be deemed to be ALARP and ALARA “unless there are strong and compelling reasons to the contrary.”
The NRR authors looked outwards from the application of the principles and found “a culture of risk aversion in both regulators and dutyholders”. Requirements on updating technology and practice have also become tools in the ‘ratchet’ that moves the ALARA baseline.
A requirement to use ‘relevant good practice’, “has become far too prescriptive in the pursuit of risk reduction” and its rigid application leads to “excessive nugatory effort and the stifling of innovation”. Relevant good practice is often applied (and accepted) as mandatory and this leads to more demanding practice over time with no clear link to an increase in risk.
Environmental protection guidance that requires use of the ‘best available technology’ (BAT) has a similar effect.
The NRR says both the Office of Nuclear Regulation (ONR) and environmental regulators should update guidance “to remove the potential for misinterpretation” of these two principles “and to prevent them from being used as a set of prescriptive requirements for dutyholders”.
If dose targets are set too conservatively they promote the elimination of risk, instead of optimisation and planning. Dose targets were lowered in 2006, but this was to reflect declining average dose levels in the nuclear industry. The ONR itself noted that they “were not prompted by reviews of risk estimates, which did not change significantly.” The result is that the UK sets target dose levels below the levels needed to ensure the safety of the public and workers in normal operation.
The UK NRR considered whether there was a fixed level at which a risk could be deemed to be ALARP, but decided that ‘directions’ such as that on tolerability of risk would establish the appropriate presumptions that will ensure proportionality. It also did not propose to abandon the concept of ‘relevant good practice’, saying it was particularly useful when managing lower-hazard activities, without detailed safety cases.
Can consistency be maintained?
Consistency on dose limits also concerns the UK and US commentators. This applies across nuclear industries around the globe, between civil and defence nuclear sectors, and between the nuclear power industry and other industries where nuclear exposure is possible.
The UK’s NRR says UK nuclear industry dose rates are “below levels recommended internationally, those adopted by many other countries, and those in non-nuclear applications (for example medical uses) in the UK.” There are many other industries that involve the use of nuclear sources and there should be appropriate read-across with the nuclear industry.
The INL paper complains that radiation protection standards vary and are inconsistent even within the US. For example NRC and DOE both maintain an occupational dose limit of 5,000mrem per year, but the DOE adds an administrative control level of 2,000mrem per year. In some cases US agencies adopt more restrictive recommendations similar to those used in the global community. In others, “overly restrictive dose-limit recommendations have not been implemented within the US because they would significantly impact current nuclear operations and hinder the promotion of domestic nuclear energy”.
Variability has implications for the global initiative to standardise reactor design and construction. The INL paper says the US is the leader in nuclear-energy development and usage. When US reactor developers propose new designs, they typically follow NRC-developed design criteria; however, this will also include consideration for international markets and these differences are factored in. It says that “Knowing this, US regulatory policy should only consider the domestic market because international rules have such a high degree of variability”.
The NRR has similar concerns. It says overly stringent approaches are, “leading to disproportionate decisions and designs, which in many cases provide no greater protection to the public, at higher costs to the taxpayer”. The UK has higher costs for nuclear technology than its partners and international competitors. This has substantial cost implications for the design, construction and operation of nuclear plants and it “increases prices for consumers and costs for the taxpayer and reduces the competitiveness of the nuclear sector for no meaningful health and safety benefit”.
Equally it has implications for decommissioning and disposal processes. For both UK and US commentators, the consistency on nuclear exposure levels – and risk assessments that justify them – should continue throughout the entire life cycle.
Overall, neither the ALARA nor the ALARP principle is likely to be abandoned by the nuclear industry. But there is growing pressure for a reset on what efforts are considered ‘reasonable’, given what governments increasingly see as the benefits of an increase in nuclear power capacity.
