Radiation dose via oral intake of contaminated surface water. - Radioactive fallout after a nuclear explosion

The report describes the radiation dose to humans via oral intake (ingestion) of one litre water from an open vessel that has been exposed to fallout from a nuclear explosion. The calculations are performed at different times after the moment of fission and apply to the radioactive nuclides that are formed during the fission of 235U. Resulting radiation doses are stated relative to the content of activity 137Cs in the fallout and apply to a vessel with an open surface of 1.1 square meters. The total volume of the water in the vessel is estimated at 448 litres, which corresponds to a water depth of 40 cm. We assume mixing is instantaneous and the distribution of the nuclides becomes homogeneous with regard to activity concentration and nuclide content per share of volume. Since the total amount of activity in the fallout is reduced with time after the event, the radiation dose will also be reduced. The internal radiation dose is given in the form of lifetime effective radiation dose (50 years). The calculations of internal radiation dose are carried out for oral intake at alternative times between 30 minutes and 12 hours after time of fission. All results are normalized to a fallout of 105 Bq/m2 of 137Cs (T1/2 = 30 yr). The results show that if 1 litre of water is consumed 30 minutes after fission, the internal radiation dose over 50 years will be 130 mSv, while the corresponding fallout would generate an external radiation dose rate of 3.8 Sv/h. However, had the water depth been only 1 centimetre, the internal radiation dose would be just over 5 Sv. As a comparison, the external radiation dose amount to about 2 Sv if a person enters the area 30 minutes after fission and stays there for 1 hour.