Summary
After a nuclear explosion, small particles may be dispersed as fallout over large areas and cause radioactive ground deposition. Radiation doses may be received from the fallout in several ways. One such exposure pathway is the ingestion of foodstuffs contaminated by the fallout, either directly or through agricultural production in areas with ground deposition.
The Swedish Radiation Safety Authority (SSM) develops consequence analyses and other forms of support for national emergency preparedness in managing radioactive fallout, both in planning and in the form of advice during response to an event. With regard to foodstuffs, there is a need for an evidence base to support:
- the work of relevant authorities in developing preparedness to protect food supply chains in the event of fallout following a nuclear explosion
- the planning and development of measurement and analytical capabilities
- the production of situation reports and consequence analyses based on dispersion prognoses and measurements
- international cooperation for protection against radioactive fallout from nuclear explosions.
SSM has therefore studied how different types and levels of radioactive ground deposition resulting from a nuclear explosion may affect the amount of radioactive substances entering foodstuffs, what radiation doses may be received through the consumption of food contaminated by fallout, and how these doses can be limited through the application of limit values for radioactive substances in foodstuffs.
In this report, SSM presents estimates of
- radiation doses that may be received through the ingestion of contaminated food following fallout that results in radioactive ground deposition
- radiation doses that may be received if the concentration of radionuclides in foodstuffs is limited through the application of the limit values set out in Council Regulation (Euratom) 2016/52 (‘the Council Regulation’)
- the levels of radioactive ground deposition at which these limit values may risk being exceeded in food produced in the contaminated area.
The estimates are based on modelling carried out on behalf of SSM by the Technical University of Denmark (DTU). In the modelling, transfer factors have been derived to describe the transfer of radioactive substances in ground deposition to different types of foodstuffs.
Results from dispersion calculations of the type used in SSM’s report 2023:05, Radiological Consequences of Fallout from Nuclear Explosions, indicate that areas with significant fallout could arise at distances of up to approximately 150 km from the explosion, covering an area of up to approximately 800 km2 following a ground-level nuclear explosion with a yield of 100 kilotons.[1] Here, ‘significant fallout’ refers to fallout that, 48 hours after the explosion, results in an effective dose rate from the ground of several millisieverts per hour.
The analysis presented by SSM in this report shows that, in the absence of countermeasures, committed effective doses approaching one thousand millisieverts could be received through single intakes at an early stage (the first two months after the explosion) of food from areas with significant fallout as described above. Radiation doses at that level may cause acute radiation injuries. Possible annual doses during the second year from the ingestion of food from areas with significant fallout have also been estimated. These estimates show that, without protective actions, committed effective doses exceeding one hundred millisieverts could be received during the second year after fallout. Radiation doses at that level imply a significantly increased risk of developing cancer.
The analysis also shows that the application of the limit values set out in the Council Regulation may result in annual doses from the ingestion of foodstuffs contaminated by fallout following a nuclear explosion being limited to a few tens of millisieverts or less. Under the conditions otherwise assumed in establishing the Council’s limit values[2], radiation doses from food can likely be kept below the reference level (one millisievert committed effective dose per year) on which the limit values are based. Consequently, these limit values have been used to estimate the levels, expressed for example in measurable quantities such as dose rate, of radioactive ground deposition from fallout following a nuclear explosion that could lead to exceedance of the limit values in foodstuffs.
[1] At shorter distances and over smaller areas, significantly higher ground deposition may occur, while at greater distances and over larger areas, lower ground deposition may occur.
[2] It is assumed, in particular, that one tenth of food intake consists of foodstuffs contaminated up to the specified limit values, and that the remaining proportion of intake consists of uncontaminated food.