Civil nuclear accident

Impact 5
upper risk error bar
upper likelihood error bar risk indicator
lower likelihood error bar
lower impact error bar
Impact & Likelihood
Impact key
5 Catastrophic
4 Significant
3 Moderate
2 Limited
1 Minor
Likelihood key
5 >25%
4 5-25%
3 1-5%
2 0.2-1%
1 <0.2%


Civil nuclear power is of strategic importance to the UK’s energy resilience and clean energy transition, and is a safe and effective mode of generating electricity. Only a small number of accidents have occurred worldwide since the first commercial nuclear power station came into operation in 1956. As required by UK regulations, there are robust safety procedures in place at all UK nuclear sites meaning an event of this type is of very low likelihood.


In line with international good practice, the UK’s domestic legislation requires planning for a range of scenarios, including those far beyond a reasonable worst-case. The scenario used for this assessment is therefore extremely unlikely. It is based on an accident occurring at a UK civil nuclear site that results in a release of radiological material that extends beyond the boundary of the site.

Onsite casualties could require decontamination, monitoring and treatment. No immediate fatal health effects would be anticipated offsite but there could be offsite casualties suffering from the effects of radiation. There could also be an increase in the risk of longer-term health impacts, such as cancers.

The resulting contamination could affect the environment and food production, and there could be disruption to domestic and international transport. The overall impacts of a release are highly dependent on weather patterns.

Key assumptions

Scientific modelling has been used to determine the scenario and the countermeasures required.


Smaller-scale scenarios could occur, which would decrease the risk to people, the environment and the economy.

Response capability requirements

There would be a large-scale, multi-agency response. A communications campaign would be needed to communicate key messages to the public. Protective actions would be promptly implemented to protect people’s health, which based on the nature of the accident, could include sheltering, evacuation or the use of stable iodine. A ready stockpile of stable iodine tablets could be required as a medical countermeasure. Immediate capabilities could include radiation monitoring and decontamination services, alongside remediation services to restrict the spread of radioactive material. Humanitarian services would also be required to support those displaced, including but not limited to emergency shelter, food and water.


Around affected parts of the UK, there could be significant and prolonged long-term health, environmental and economic impacts requiring sustained recovery.