Radiation doses from the use of peat-fuel in heating power plants

The radiation doses and the need for radiological protection arising from the use of peat-fuel that contain naturally occurring radionuclides and 137 Cs are assessed. Dose calculations for the worst case are performed for two reference ashes, one containing normal concentrations of radionuclides and the other containing high concentrations. The concentrations of radionuclides in the normally active ash reflect the median value of U and Th in energy producing peat bogs. The concentrations in the highly active ash were chosen in such a way that not more than 5 percent of the peat bogs would exceed the values. The doses have been estimated for workers and the general public for different exposure pathways. These are 1) harvesting and handling of peat, 2) releases from heating plants, 3) land filling, 4) landscaping and 5) handling of ashes. Under normal circumstances the resulting doses from the normally active ash are insignificant (<0.01 mSv/year). For the highly active ash the doses are below 0.1 mSv/year under the assumptions made in the investigation. For the general public the doses are also insignificant for the highly active ash except for the influence of a landfill. The dose estimates of the influence from leached water from a landfill are very uncertain due to that too few measurements of environmental samples have been carried out. At today's production of 3.5 TWh per year the peat-ash can amount to between 30,000 and 60,000 tons per year. Today the Swedish Geological Survey limits the dose from peat-use informally. They advise against the harvesting of peat with a uranium content exceeding 200 ppm in an ashed peat sample, which corresponds to 2,470 Bq/kg of 238 U. The resulting doses are estimated to be about half of those estimated for the highly active ash. Thus 10 percent of otherwise suitable peat land is not harvested