Determination of 129I in biomonitors collected in the vicinity of a nuclear power plant by neutron activation analysis

Abstract

Neutron activation analysis (NAA) was used to determine 129I and the 129I/127I ratio in bovine thyroid, moss, and river sediment samples collected in the vicinity of the Temelin nuclear power plant (NPP) in south Bohemia. The NAA procedures comprised pre-irradiation separation of 129I by combustion of the samples in the stream of oxygen at 1,000 °C and trapping the liberated iodine in a LiOH/(NH4)2SO3 solution. Post-irradiation separation of 130I produced by the reaction 129I(n,γ)130I was carried out by extraction of elementary iodine with chloroform followed by precipitation of PdI2. Nondestructive, epithermal NAA was used to determine 127I employing the 127I(n,γ)128I reaction. The results showed that mean values of 129I and the 129I/127I ratio in the bovine thyroids varied from 22 to 61 mBq kg−1 (dry mass) and 2.8 × 10−9 to 5.4 × 10−9, respectively. These values are close to the lower end of results reported from various regions non-polluted with 129I. No significant differences were found between 129I concentrations and the 129I/127I ratios in the bovine thyroids collected prior to the start and after several years of operation of the NPP. The mean value and standard deviation of 129I in mBq kg−1, dry mass and the 129I/127I ratio in moss Pleurozium schreberi were 23 ± 16 and 2.3 × 10−9, respectively, whereas values of 129I in the river sediments were below 8–10 mBq kg−1 (dry mass) after several years of the NPP operation.