Analysis of the health of Sellafield workers in the National Registry for Radiation Workers (NRRW)
The main aim of the NRRW is to evaluate the impact of radiation exposure on the risks from both cancer and non-cancer diseases.
Summary
The main aim of the National Registry for Radiation Workers (NRRW) is to evaluate the impact of radiation exposure on the risks from both cancer and non-cancer diseases.
Sellafield workers form an influential part of the NRRW since, as a group, they have long follow-up, starting from the late 1940s, and bigger external doses compared to other worker groups.
In addition to their external exposure, around half of Sellafield workers have been recorded as being monitored for internal radiation exposure, primarily to plutonium and uranium. However, analyses of the risks of external exposure among these workers have, to date, only ever taken account of the fact of internal monitoring and not incorporated individual estimates of the doses to the internal organs from plutonium and uranium.
This project will undertake a first analysis of the risks of cancer incidence and all causes of mortality among the Sellafield workforce based on external dose estimates and separate internal organ dose estimates.
It will provide the first direct evidence of the possible differences in the effects of external radiation on health between workers who only have external exposure and those who also have internal exposure where quantitative measures of internal organ dose is available. It will also provide the first direct evidence for the effects of internal exposure on risks of cancer and non-cancer diseases among these workers.
These results will inform on how the next analysis of the whole NRRW cohort (NRRW4) is carried out.
Background information
Previous analyses of the Sellafield worker cohort
To date, the only analysis of Sellafield workers that has used separate estimates of internal and external radiation dose was a pooled study of Mayak and Sellafield plutonium workers that examined only lung cancer risk with follow-up to 2005 (2).
The last analysis of Sellafield workers as a whole group was published in 1999 (2). It examined disease risks to 10,000 radiation workers, of these 5,000 workers were only exposed to external radiation and 5,000 were workers who were also monitored for internal exposure to plutonium. Risk in the latter group was based on their total dose from both sources no separate estimates of risk related to internal exposure were provided. Follow-up for this analysis was to 1993.
In 2014, cancer mortality and incidence was examined in the whole BNFL cohort as a single group (Sellafield, Springfields, Capenhurst and Chapelcross) comprising 42,000 radiation workers and 22,000 non-radiation workers with follow-up to 2005 in relation to external dose but with no consideration of internal dose beyond a yes/no indicator variable for internal monitoring status (1).
Updates to the cohort (figures are preliminary)
Since the BNFL cohort was merged into the NRRW in 2023 bioassay data about all the Sellafield workers monitored for internal exposure has been processed onto the NRRW. This includes data for approximately 8,500 workers first employed from 2004 who were not part of the original BNFL cohort.
The Sellafield radiation worker group in the NRRW now comprises around 32,000 workers who were monitored for external exposure and of these 16,000 have at least one piece of bioassay data providing evidence of their being monitored for internal exposure.
Follow-up for this analysis will be to the end of 2023 which extends the follow-up over the last Sellafield specific analysis by 30 years. Therefore, the proposed analysis should be considerably more informative due to additional deaths and cancer incidences recorded during those 30 years.
Statistical analyses to be carried out
Estimates of rate ratios and standardised mortality and cancer incidence ratios
The mortality from all diseases and cancer incidences among the radiation workers will be compared to a group of non-radiation workers employed at Sellafield (this is a fixed group of workers employed up to 2004 that NRRW inherited when the BNFL cohort was merged into NRRW). Disease rates in both radiation and non-radiation worker groups will also be compared to those of England and Wales population.
Dose response analyses
For a range of diseases, where sufficient events occur, estimates of a dose response relationship will be derived.
In the first instance, linear dose response relationships will be fitted to estimate any association between excess disease risk and cumulative radiation dose (both external and internal). The quality of the fit of the linear relationship will be tested against other possible relationships, for example, linear quadratic and linear exponential, to find the ‘best’ one.
Variation in the dose response relationship with factors age, sex, calendar period, time since first exposure and duration of exposure will be evaluated.
Further analyses may be carried out as appropriate depending on what is found from those described above.
Information governance
This analysis of Sellafield worker data was approved by the NRRW Governance Group at their meeting on 4 July 2025. A favourable opinion for the project was granted by the UKHSA Research and Ethics Governance Group (REGG) on 1 August 2025.
(The REGG has been established to provide an appropriate level of authoritative and independent review of UKHSA led studies that involve human participants, their data and/or their tissues. The REGG can confirm study classification and advise on governance and research regulations. REGG review is compulsory for all UKHSA led research studies that do not fulfil the criteria for review by an NHS Research Ethics Committee (REC)).
The NRRW has a study-specific privacy notice which provides more information about the processing of worker data.
Publication of the results
The results are planned to be published in 2 papers, one focusing on cancers and the other on non-cancer diseases. Additional papers may also be considered depending on what is found during the analyses.
All papers will be published open access. Details of where to find the papers and layman’s summaries will be added here.
The study team will present the results at scientific conferences aimed at informing the national and international radiation protection community about the work. The NRRW Governance will be consulted as to appropriate ways to inform the Sellafield workforce about the results.
References
1. Gillies M and R. Haylock (2014). ‘The cancer mortality and incidence experience of workers at British Nuclear Fuels plc, 1946-2005’ Journal of Radiological Protection 2014: volume 34, issue 3, pages 595 to 623
2. Gillies M, Kuznetsova I, Sokolnikov M, Haylock R, O’Hagan J, Tsareva Y and Labutina E (2017). ‘Lung Cancer Risk from Plutonium: A Pooled Analysis of the Mayak and Sellafield Worker Cohorts’ Radiation Research 2017: volume 188, issue 6, pages 645 to 660
3. Omar R Z, Barber JA and Smith (1999). ‘Cancer mortality and morbidity among plutonium workers at the Sellafield plant of British Nuclear Fuels’ British Journal of Cancer 1999: volume 79, issues 7 to 8, pages 1,288 to 1,301