Indoor and Outdoor Exposure to Radon, Thoron and Thoron Decay Products in a NORM Area with Highly Elevated Bedrock Thorium and Legacy Mines.

Radon (222Rn) and thoron (220Rn), and especially their short-lived decay products, are major contributors to dose received by the public from naturally occurring radioactive material (NORM), particularly in areas with elevated levels of naturally occurring radionuclides. Mining in such areas can involve ventilation of high amounts of these gases, which may influence outdoor levels. In this work, we assessed indoor and outdoor levels of 222Rn, 220Rn and 220Rn decay products (TnDP) in close proximity to an area with elevated bedrock levels of thorium (232Th) and a NORM legacy mining site with high natural ventilation. We assess municipal buildings at distances from a few hundred meters to 2 km from the NORM legacy mines. In some buildings, high indoor levels of 222Rn were observed in winter, as expected for temperate areas. In summer, high indoor levels of 222Rn and 220Rn were observed in some buildings, and very low associated levels of TnDP in actively ventilated buildings may suggest entry by ventilation and an outdoor source. Outdoor levels of TnDP increased with decreased distance from the legacy mines, suggesting dispersal from these during both summer and winter.

The impact of tidal and mesoscale eddy advection on the long term dispersion of 99Tc from Sellafield.

In the present work, numerical models are used to study the fate of the 99Tc discharges from Sellafield with a specific focus on the role of mesoscale eddy and tidal advection on the transport and dispersion of this radionuclide. Transport estimates are made with an ocean model that resolves a large part of the ocean mesoscale eddy field and also includes tides. Equivalent estimates are also computed with another model in which these processes are either absent or parametrized. Comparison with field observations shows that the coarse-resolution model can reproduce the general features of the observed time-space 99Tc distribution if the diffusivity in its eddy parametrization scheme is suitably chosen. However, the eddy-permitting simulations capture regional details better and show an overall higher prediction skill, with the model predictions agreeing with the observations within a factor of two to four. The importance of tidal advection is investigated by comparing transport in the eddy-permitting model when this is run either with tides included or with tides filtered out. The results point to systematic Lagrangian tidal drift in the Irish Sea and the North Sea that eventually impacts the 99Tc activity concentration levels also far downstream.