SPECIAL REPORT | ALARA
The ‘Tolerability of Risk’ principle
The UK Nuclear Regulatory Review says the existing risk management framework can be highly effective if interpreted and implemented appropriately. “It encourages a proportionate approach to safety, ensuring solutions are only enacted if ‘reasonably practicable’ and that sufficient consideration is given to the impact in terms of time, money, and trouble”. It is based on the so-called ‘Tolerability of Risk’ triangle. This has an ‘unacceptable region’, and
below it a ‘tolerable region’ where risks are tolerable if reduced ALARP. In the ALARP (or tolerable) region the cost-benefit balance is between the costs (which in case law
is money, time or trouble) of introducing safety measures, against the risk-reduction benefits of those safety measures. With very low risks there is a further region called the ‘broadly acceptable region’ in which, although risks must be ALARP, regulators will not push to reduce them further. Implicit in these ideas is that risks are tolerable because of the individual and societal benefits gained from the activities that are generated by them. ■
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
16 | December 2025 |
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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. ■
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