Using a chain of models to predict health and environmental impacts in Norway from a hypothetical nuclear accident at the Sellafield site

When a nuclear accident occurs, decision makers in the affected country/countries would need to act promptly to protect people, the environment and societal interests from harmful impacts of radioactive fallout. The decisions are usually based on a combination of model prognoses, measurements, and expert judgements within in an emergency decision support system (DSS). Large scale nuclear accidents would need predictive models for the atmospheric, terrestrial, freshwater, and marine ecosystems, for the connections between these in terms of radionuclide fluxes, and for the various exposure pathways to both humans and biota. Our study showed that eight different models and DSS modules could be linked to assess the total human and environmental consequences in Norway from a hypothetical nuclear accident, here chosen to be the Sellafield nuclear reprocessing plant. Activity concentrations and dose rates from ¹³⁷Cs for both humans and the environment via various exposure routes were successfully modelled. The study showed that a release of 1% of the total inventory of ¹³⁷Cs in the Highly Active Liquor Tanks at Sellafield Ltd is predicted to severely impact humans and the environment in Norway if strong winds are blowing towards the country at the time of an accidental atmospheric release. Furthermore, since the models did not have built-in uncertainty ranges when this Sellafield study was performed, investigations were conducted to identify the key factors contributing to uncertainty in various models and prioritise the ones to focus on in future research.

Modelling Environmental Impacts of Cesium-137 Under a Hypothetical Release of Radioactive Waste

Waste tanks at the nuclear facility located at Sellafield, UK, represent a nuclear source which could release radionuclides to the atmosphere. A model chain which combines atmospheric transport, deposition as well as riverine transport to sea has been developed to predict the riverine activity concentrations of ¹³⁷Cs. The source term was estimated to be 9 × 10⁴ TBq of ¹³⁷Cs, or 1% of the assumed total ¹³⁷Cs inventory of the HAL (Highly Active Liquid) storage tanks. Air dispersion modelling predicted ¹³⁷Cs deposition reaching 127 kBq m^-2 at the Vikedal catchment in Western Norway. Thus, the riverine transport model predicted that the activity concentration of ¹³⁷Cs in water at the river outlet could reach 9000 Bq m^-3 in the aqueous phase and 1000 Bq kg^-1 in solid phase at peak level. The lake and river reaches showed different transport patterns due to the buffering effects caused by dilution and slowing down of water velocity.

Impacts on the terrestrial environment in case of a hypothetical accident involving the recovery of the dumped Russian submarine K-27

Objects containing radioactivity have been routinely dumped in Arctic waters near NW Russia up until the 1990s. One of the most radioactive objects in this region, the nuclear submarine K-27, was dumped in Stepogovo Fjord and contained spent nuclear fuel (SNF). Although the two K-27 submarine reactors were mothballed before dumping, concerns about the potential long term risks of contamination remain and plans to retrieve and decommission K-27 exist. In this article, human dose and environmental impact aseessments are presented for two possible future scenarios involving: (1) an ingress of water into a reactor in situ leading to a spontaneous chain reaction (SCR) and (2) an on-board fire when SNF is being removed at the mainland decommissiong site at Gremhika Bay on the Kola Peninsula. Assessments have been completed using conservative assumptions, focusing on possible effects to Norwegian territory. Atmospheric transport and deposition of radioactivity was modelled near field and regionally, using appropriate models, whilst human doses and environmental exposures were modelled using a standard IAEA approach and the ERICA tool, respectively. Results indicate that large areas of Norwegian territory could be affected by fallout from the Gremhika scenario, especially in the north, though at levels two orders of magnitude lower than those observed after the Chernobyl accident. Potential doses, primarily due to ground shine, to a critical group of personnel on-site at Stepogovo resulting from a SCR could require preventative measures based on ICRP recommendations (20-100 mSv). Doses to non-human biota in Norway for the Gremhika scenario would be negligible, typical of background dose rates for terrestrial organisms.