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Frequently asked questions

How does ONR ensure that nuclear licensed sites remain safe against climate change?

ONR guidance

  • ONR requires licensees to demonstrate resilience to climate change and its effects. ONR's expectation is for the effects of reasonably foreseeable climate change to be taken into account over the lifetime of a facility. This expectation is included in ONR's Safety Assessment Principles, with further guidance provided in the External Hazards Technical Assessment Guide (TAG 13).

Safety cases

  • All licensees are required to produce a nuclear safety case which ONR assesses in line with its guidance. Within the safety case, ONR expects licensees to conservatively derive the site's external hazards design basis events and to demonstrate that the site and its facilities are resilient to external hazards, including reasonably foreseeable climate change. For more information on safety cases see ONR's Technical Assessment Guide on The Purpose, Scope and Content of Safety Cases.

Relevant good practice

  • ONR expects licensees to keep a watching brief on climate change and to take account of advances in relevant good practice in updates to their safety cases.
  • ONR maintains regular engagement with licensees to ensure that updates to relevant good practice, such as UKCP18, are appropriately considered by licensees.

Periodic Safety Reviews

  • ONR ensures that safety cases are updated through Periodic Safety Reviews (PSRs). As part of this, licensees are expected to consider advances in climate change predictions and identify any impact on claims made in their safety cases and any subsequent measures that need to be implemented. Further information on PSRs can be found in ONR's Periodic Safety Reviews Technical Assessment Guide (TAG 50) and Licence Condition 15, detailed in the Licence Condition Handbook.

What is the difference between external and natural hazards?

  • External hazards include both natural and man-made hazards that originate externally to the site and its processes, i.e. the licensee may have very little or no control over the initiating event. For example, earthquakes, accidental aircraft crash or off-site chemical release.  
  • Natural hazards are a subset of external hazards that originate due to natural processes. Examples of natural hazards include earthquakes, extreme weather and coastal flooding.
  • ONR has a specific team dedicated to the consideration of external hazards that sits within its Civil Engineering and External Hazards Specialism.

What is the design basis? And is climate change included?

  • For natural hazards the design basis is the 1 in 10,000 year event, conservatively defined – this is an event that has a 1 in 10,000 chance of occurring or being exceeded in any given year. For natural hazards impacted by climate change, for example meteorological and coastal flood hazards, the design basis needs to include reasonably foreseeable climate change over the lifetime of the facility.
  • Once the design basis has been defined, licensees must demonstrate to ONR that their facility can withstand the design basis event. Licensees also need to consider beyond design basis events, which must not result in a sudden or dramatic change in consequence – commonly referred to as ‘cliff-edge' effects.

What does reasonably foreseeable climate change mean?

  • ONR's expectation is that the reasonably foreseeable effects of climate change over the lifetime of the facility should be taken into account by licensees. As a non-prescriptive regulator, ONR does not provide a definition of reasonably foreseeable climate change or specify how the effects should be addressed. The reasonably foreseeable effects of climate change are site and technology dependent and are the responsibility of the licensee to justify.
  • ONR expects licensees to use relevant good practice for determining climate change effects, such as UKCP18.

What does beyond design basis mean in relation to climate change?

  • For natural hazards, beyond design basis refers to events that have a less than 1 in 10,000 chance of being exceeded in any given year – this means that they have a smaller chance of occurring than design basis events. It is important for licensees to consider beyond design basis events to confirm the absence of ‘cliff-edge' effects just beyond the design basis.
  • A ‘cliff-edge' is where a small change in analysis assumptions, such as those relating to design basis hazard severity, facility response, or design basis analyses, is predicted to lead to a disproportionate increase in the radiological consequence.
  • ONR's expectation is that a small change in design basis fault or event assumptions must not lead to a disproportionate increase in the radiological consequences.

What is the managed adaptive approach?

  • One way to address the significant uncertainty surrounding climate change in the future is by adopting the managed adaptive approach. This is detailed in the ONR and Environment Agency Joint Advice Note Principles for Flood and Coastal Erosion Risk Management.
  • The aim of the managed adaptive approach is to build flexibility into options selected and decisions made today, so they can be adjusted in response to what happens in future, to ensure that sites remain safe. The managed adaptive approach is appropriate, given current climate change uncertainty and the timescales for the development of the effects on sea level and meteorological events. For the managed adaptive approach to be suitable, it's necessary to demonstrate that it is made up of:
    • Technically feasible and viable options - i.e. that the future cost of the options can be accounted for.
    • The lead time between the need for an option being triggered and implemented is achievable.
    • The fullest range of risks has been accounted for through the use of the credible maximum scenario.
  • An example of the managed adaptive approach is the design and construction of a sea wall that can be built higher should future sea level rise be greater than is currently expected. This would require the identification of trigger points, for the start of the extra height construction, to ensure that the site always remains protected against sea level rise.

Why doesn't ONR specify the sea level height that licensees must design to, in order to protect against climate change?

  • ONR requires licensees to demonstrate that their site is adequately protected against the design basis sea level, which includes reasonably foreseeable climate change. This includes the future effects of climate change on wave and tide height as well as the static sea level. The design bases are defined at a site-specific level because hazard severity differs depending on the locality of the site. For example, one site may be more vulnerable to sea level change whereas another may be more susceptible to high air temperature. The site-specific approach ONR has adopted ensures licensees are able to best protect against the site's hazards.

What is UKCP18?

  • The UK Climate Projections 2018 (UKCP18) have been produced by the Met Office with expert input from the Environment Agency and are funded by the UK Government. UKCP18 projections have been developed from recent advances in modelling the climate system. The use of the new Met Office supercomputing facilities has enabled higher resolution climate projections to be produced compared with UK Climate Projections 2009 (UKCP09). UKCP18 updates the UKCP09 projections over UK land areas and updates UKCP09 projections of sea level rise, giving greater regional detail and providing more information on the potential extremes of climate change.

What are ONR's expectations for UKCP18's use?

  • ONR recognises that the impacts of climate change on hazard magnitude and frequency for some natural hazards could be significant over the lifetime of new nuclear sites. The use of UKCP18 is considered to be relevant good practice in determining climate change allowances. ONR expects licensees to take account of UKCP18 when assessing the impacts of climate change. Further information on ONR's expectations with regards to UKCP18 is available in the document Use of UK Climate Projections 2018 (UKCP18) by the GB Nuclear Industry.

How does ONR keep up-to-date with advances in climate science?

  • Climate change is a fast evolving field of science. Therefore, it is important that ONR is aware of advances in scientific thinking and is in a position to respond appropriately.
  • One way ONR maintains its awareness is through its Expert Panel on Natural Hazards. The Expert Panel provides ONR with independent expert advice on natural hazards, including climate change. ONR is in regular contact with panel members and, in addition to this, hosts an annual Expert Panel meeting for each of the two sub-panels (the Sub-Panel on Meteorological and Coastal Flood Hazards and the Sub-Panel on Seismic Hazards).
  • In addition to the Expert Panel, ONR maintains links with organisations involved in climate change research and engages with the environment agencies on cross-cutting matters, such as climate change.
  • ONR also encourages and supports staff participation in climate change conferences and training courses.

What are the responsibilities of ONR and the environment agencies on nuclear licensed sites for climate change?

  • ONR is responsible for regulating nuclear safety on nuclear licensed sites. ONR expects licensees to demonstrate that they have adequate arrangements in place to manage risks throughout the lifetime of the site, including those arising from climate change.
  • For clarity, ONR regulates the safety of nuclear installations (including conventional safety) and the transport of radioactive materials in Great Britain. It also regulates nuclear security and safeguards in the United Kingdom.
  • The respective environment agencies for England (EA), Wales (NRW) and Scotland (SEPA) are responsible for environmental protection, including authorising discharges of radioactive waste from nuclear licensed sites. 
  • For more information on ONR's and the environment agencies' responsibilities see the Licensing Nuclear Installations document.

How do I learn more about how climate change is managed on nuclear licensed sites?