Coping with a big nuclear accident

Managing Nuclear Risk Issues, Environmental, Financial and Safety: The NREFS Project


The research has shown that the risk after a big nuclear accident has happened is smaller than almost everyone has realised, a result that may change fundamentally the way people think of nuclear power.  The life expectancy lost through radiation exposure after even the biggest nuclear accident can be kept small, while the downside risk is limited even in the absence of countermeasures.

Mass population movement has been shown to be a poor response to a big nuclear accident: relocation is an option that governments should use sparingly if at all.


The project was conceived in 2012 following the Fukushima Daiichi accident in Japan, which was the second case after the Chernobyl accident in 1986 where mass relocation was the primary policy response by governments. The aim of the research was to determine how best should you respond after a big nuclear accident has occurred?

Nearly three quarters of the 116,000 members of the public relocated in the first evacuation after the Chernobyl accident would have lost less than 9 months' life expectancy if they had remained in place, and only 6% would have lost more than 3 years.  The second evacuation of 220,000 4 years later served little purpose - it averted 3 months' loss of life at most.  Relocation was sensible for between 10 and 20% of the total number, 335,000, of people evacuated in total. It is difficult to justify relocating anyone after the Fukushima Daiichi accident.

The results are derived using the new Judgement- or J-value method under development in the University of Bristol's Safety Systems Research Centre.  An objective balance is struck between the expenditure on a safety measure and the loss of life expectancy it averts, with the comparison mediated by society's risk-aversion, a parameter measured using a novel method.

Radiation-induced loss of life expectancy is calculated using an extension of Marshall's method.  The Total Judgement- or JT-value extends the result to allow the assessment of systems that protect against both human and environmental harm.

The NREFS project applied mathematical methods and models as aids to penetrate the fog of uncertainty and confusion following a major nuclear accident. It was supported by funding from EPSRC.


The project used three different mathematical methods:

1.J-value (J for Judgement) assessment applied to the Chernobyl and Fukushima Daiichi accidents (led by City, University of London then University of Bristol)

The J-value is able to explain 80% of the variation in life expectancy with GDP per head for 162 out of the 193 nations recognised by the UN. This method emerges as an accurate description of the intuitive approach to assess health and safety decisions all over the world.

2.Optimal economic control (including health effects) applied to hundreds of conceivable big nuclear accidents worldwide (led by Manchester University)

The economic strategies based on Bellman's principle of optimality found that relocation was not needed in any of the hundreds of base case major nuclear accidents they considered, and only rarely in their sensitivity studies.

3.Public Health England's nuclear accident consequence codes, PACE-COCO2, applied to a big accident at a fictional nuclear reactor located between Southampton and London (led by the Open University).

The application of Public Health England's PACE-COCO2 programme suite to a severe accident on a fictional reactor located on the South Downs of England suggested that the expected number of people needing relocation was 620, orders of magnitude less than the mass exoduses at Chernobyl and Fukushima.

Impact of the Research

The results were presented in Parliament to the All-Party Parliamentary Committee on Nuclear Power on 11 March 2015, and at a follow-on meeting with the Chief Scientific Adviser to the Department of Energy and Climate Change.  Discussions have been held with the Chairman of Japan's Nuclear Damage Compensation and Decommissioning Facilitation Corporation.

The French Institute of Radiation Protection and Nuclear Safety (the French nuclear regulator) wishes to work with the University of Bristol to extend and apply the NREFS results.  Professor Thomas has submitted evidence based on NREFS to the BEIS/MoD/HSE 2017 Public Consultation on the "Revised requirements for radiological protection: Emergency preparedness and response".

The formal results of this research project were published in November 2017 and were marked by a conference and public lecture held at the University of Bristol.  The public lecture can be watched below:

The launch of these findings provoked significant mass media interest, including The ConversationThe Times (paywall)The Evening Standard  and the BBC. The best coverage was collated by the South West Nuclear Hub in a news article in November 2017.

Application to Industry

Dr MP O'Donnell, Head of Research and Development, EDF Energy, Nuclear Generation wrote to Professor Thomas after the presentation in Parliament:

" 2 senior EDF Energy directors were present at the meeting of the All-Party Parliamentary Group in London where you set out the conclusions of the NREFS project. I know both my colleagues were impressed with the range and quality of the work and your ability to highlight its conclusions in a way that was accessible to a wide audience that included Members of the UK Parliament."

Professor Philip Thomas

Philip Thomas is a Professor of Risk Management in the Faculty of Engineering. He gained over 20 years' experience working in the chemical and nuclear industries, including roles with ICI and UKAEA/ AEA Technology. Before moving to the University of Bristol in 2015, he held a Chair in Engineering Development at City, University of London.

His research interests include:

  • control
  • instrumentation
  • nuclear decommissioning
  • risk assessment and economics
  • legal implications

Further Reading

The website for this project is

The 10 closing papers of the NREFS study were published as Special Issue of Process Safety and Environmental Protection in November 2017.

University of Bristol press release