Determination of 129 I in biomonitors collected in the vicinity of a nuclear power plant by neutron activation analysis
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Determination of 129I in biomonitors collected in the vicinity of a nuclear power plant by neutron activation analysis Ivana Krausova´ • Jan Kucˇera • Ivo Sveˇtlı´k
Received: 14 August 2012 / Published online: 13 September 2012 Ó Akade´miai Kiado´, Budapest, Hungary 2012
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 Temelı´n 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,c)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,c)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 9 10-9 to 5.4 9 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 129 127 I/ I 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 9 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. Keywords 129I Biomonitor Thyroid gland Neutron activation analysis Nuclear power plant
I. Krausova´ J. Kucˇera (&) I. Sveˇtlı´k Nuclear Physics Institute ASCR, 25068 Rˇezˇ 130, Czech Republic e-mail: [email protected]
Introduction The long-lived, beta-emitting radionuclide 129I (half-life 1.57 9 107 years) occurs in the environment as a result of both natural processes and human nuclear activities. The former processes involve the spallation reaction of highenergy cosmic rays with xenon in the upper atmosphere, spontaneous fission of 238U, thermal neutron-induced fission of 235U, and to a lesser extent the neutron activation reactions 128Te(n,c,b-)129I and 130Te(n, 2n)129I. These processes resulted in the formation of about 180 kg of 129I in the hydrosphere and about 60 kg in the lithosphere (total at about 250 kg) and caused a representative atom ratio of 129 127 I/ I at 1.5 9 10-12 in the hydrosphere [1]. The human nuclear activities include neutron-induced fission of 235U and 239Pu in the explosion of nuclear devices, as well as the operation of nuclear reactors for research and power production. Of these, reprocessing of spent nuclear fuel is the major source of environmental pollution with 129I, mainly of the marine environment, as schematically depicted in Fig. 1, which shows releases of 129I i
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