Determination of long-lived radionuclides in environmental media around a nuclear fuel reprocessing plant

Methods for the analysis of¹²⁹I and²⁴¹Pu are described briefly. Neutron activation is necessary to achieve an adequate degree of sensitivity for the measurement of¹²⁹I, but otherwise all laboratory manipulations are straightforward and use commonly-found, well-tried techniques. With these methods, both radionuclides can be measured easily in the terrestrial environment around a nuclear fuel reprocessing plant;²⁴¹Pu is measureable elsewhere in integrating media such as undisturbed soil.     

Determination of 129I/127I ratios in environmental samplesusing neutron activation analysis

Studies on the behavior of ¹²⁹I in the environment are greatly enhanced when the concentration of the radioiodine can be related to stable ¹²⁷I. The background ratios of ¹²⁹I/¹²⁷I of 10^-10 and lower, found in uncontaminated areas, are best measured using accelerator mass spectrometry. However, there are many examples of studies where ratios higher than 10^-8 have been measured, even in places located remotely from nuclear reprocessing activities. In the vicinity of reprocessing plants it is possible to find ratios between 10⁰ and 10^-7, which can be detected easily using neutron activation analysis (NAA). Stable iodine is readily determined at concentrations below 1 mg/kg in environmental materials with instrumental NAA and radiochemical techniques can be used to measure ¹²⁹I to below mBq concentrations. Therefore, where there are elevated concentrations of ¹²⁹I it is possible to use a combination of neutron activation techniques to determine ¹²⁹I/¹²⁷I ratios. This paper describes how NAA is used to measure ¹²⁹I/¹²⁷I ratios in milk, vegetation, and atmospheric samples. Instrumental NAA is used to measure both ¹²⁹I and ¹²⁷I where the ratio is between 10⁰ and 10^-3. A radiochemical procedure is used to measure ¹²⁹I at ratios between 10^-3 and 10^-7, with a thermal neutron flux of 10¹⁶ m^-2·s^-1.     

Determination of iodine-129 and iodine-127 in environmental samples collected in Japan

Analytical method for the determination of¹²⁹I and¹²⁷I in environmental samples has been developed by using radiochemical neutron activation analysis. The¹²⁹I levels in the samples such as soil (0.9–41 mBq/kg), precipitation (0.002–0.11 mBq/kg), pine needles (1.2–32 mBq/kg) and seaweed (<0.1–17 mBq/kg) collected near the nuclear facilities in Tokaimura were higher than those from the other areas in Japan. The highest¹²⁹I concentration was found in surface soil (0–5 cm), and the highest¹²⁹I/¹²⁷I ratios were found in pine needles and precipitation. The¹²⁹I/¹²⁷I ratio was higher in rice paddy soil than those in wheat field soil collected around Tokaimura, while the concentration of¹²⁹I somewhat higher in wheat field soil.     

Dry deposition velocity of iodine-129 onto grass as obtained by field measurements in the environment of a nuclear fuel reprocessing plant

The deposition velocity of gaseous organic¹²⁹I species from the exhaust air stack of the Karlsruhe reprocessing plant onto pasture grass was measured by a field experiment. By simultaneously measuring the amount of¹²⁹I deposited per unit area of pasture grass and the time integrated mean air concentration of¹²⁹I a deposition velocity of V_g=5.8×10^–1 /cm s^–1/ onto pasture grass was determined.     

Very accurate,simultaneous determination of trace amounts of Co and Ni in biological materials by radiochemical neutron activation analysis

A very accurate and sensitive method for the simultaneous determination of trace amounts of Co and Ni in biological materials has been elaborated. The method is based on radiochemical neutron activation. Irradiation of samples in Cd-shielded channel of a nuclear reactor assures balanced activity ratio of⁵⁸Co and⁶⁰Co isotopes and favourable detection limits for both nickel and cobalt. Column chromatography (ion exchange and extraction) has been used for the quantitative and selective isolation of the determined radionuclides. High accuracy of the method has been demonstrated by the analysis of several certified reference materials.     

Application of 129I as an environmental tracer

¹²⁹I is produced naturally by cosmic-ray spallation of Xe and by spontaneous fission of ²³⁸U. In the environment ¹²⁹I is mainly due to nuclear weapon tests and reprocessing plants. The high water solubility of iodine makes ¹²⁹I a good oceanographic tracer. Long residence time and large air releases of ¹²⁹I from reprocessing plants allow ¹²⁹I to be used as a geochemical and metrological tracer. The same chemical and physical properties of ¹²⁹I and ¹³¹I enable one to use ¹²⁹I as a tool for the reconstruction of ¹³¹I doses after a nuclear accident. Some studies using ¹²⁹I as a tracer which were carried out in the author's laboratory, are summarized. This revised version was published online in July 2006 with corrections to the Cover Date.     

Iodine-129 and natural iodine-127 in deer thyroids from the environment of a small nuclear fuel reprocessing plant and from sites remote from nuclear facilities

Concentrations of the fission product¹²⁹I and natural¹²⁷I were determined in deer thyroids collected in the environment of the small Karlsruhe nuclear fuel reprocessing plant (WAK) and in a region remote from¹²⁹I sources of nuclear facilities. The isotopic ratio¹²⁹I/¹²⁷I in thyroids from the environment of WAK varies from 1.0×10^–6 to 12.9×10^–6, which is about one order of magnitude higher than the¹²⁹I/¹²⁷I ratios in thyroids from deer in a region remote from nuclear facilities. These ratios were between 0.2×10^–6 and 0.7×10^–6.     

Analysis of Iodine-129 in Environmental Materials: Quality Assurance and Applications

The long-lived radionuclide ¹²⁹I (T _1/2 = 15.7 My) occurs in the nature in very low concentrations. Since the middle of our century the environmental levels of ¹²⁹I have been dramatically changed as a consequence of civil and military use of nuclear fission. Its investigation in environmental materials is of interest for environmental surveillance, retrospective dosimetry and for the use as a natural and man-made fracers of environmental processes. We are comparing two analytical methods which presently are capable of determining ¹²⁹I in environmental materials, namely radiochemical neutron activation analysis (RNAA) and accelerator mass spectrometry (AMS). Emphasis is laid upon the quality control and detection capabilities for the analysis of ¹²⁹I in environmental materials. Some applications are discussed.     

Rapid radiochemical analysis of 131I in environmental samples using a well-type Ge-detector

Large-scale production of ¹³¹I in a nuclear reactor, the gaseous nature of ¹³¹I, and its selective uptake by the human thyroid gland, make this radioisotope a health hazard in the event of a nuclear accident. The maximum concentration of ¹³¹I in drinking water has been set at 1 pCi/l. Human ingestion of ¹³¹I through the grass-cow-milk pathway makes milk an environmentally significant matrix to be monitored for. In this paper, we report a simple and a rapid radiochemical procedure for the analysis of ¹³¹I in water and milk samples. A quick single-step separation on anion-exchange resin concentrates radioiodine from large sample volumes. The resin is then directly counted in the cavity of a low-background well-type HPGe detector that has high counting efficiency for X-rays and low-energy -radiation. Chemical recovery is evaluated from the intensity of the 29.6 keV X-rays of the ¹²⁹I spike, and ¹³¹I is assayed through the intensity of its 364.5 keV g-peak. The method's minimum detection limit is 0.5 pCi ¹³¹I based on a 1 liter sample and a 200-minute count.     

129I in soil and grass samples around a nuclear reprocessing plant

Neutron activation analysis was used to determine¹²⁹I in soil and grass samples around a reprocessing plant. The method involved wet oxidation of samples, using chromic acid, followed by distillation, collection of iodine in alkaline solution, loading on Dowex-1, irradiation and post-irradiation purification steps. The -activity of¹³⁰I isotope of the purified samples was measured for quantitative determination of¹²⁹I. The experimental results showed that¹²⁹I and the¹²⁹I/¹²⁷I atomic ratio in soil samples varied from 1.09×10^–4 to 5.33×10^–3 pCi g^–1 and 0.10×10^–6 to 6.12×10^–6, respectively. Further, the geometric mean of soil-to-plant transfer factor (Bv) for¹²⁹I was found to be 0.16 which was comparable with other published values.     

Immobilization of fission iodine by reaction with insoluble natural organic matter

Iodine-129 is a fission product and highly mobile in the environment. Along with other stable isotopes of iodine, ¹²⁹I is released during reprocessing of nuclear fuel and must be trapped to prevent the release of radioactivity to the environment. Past studies have provided evidence that iodine can become associated with natural organic matter (NOM). This research explores the use of NOM (sphagnum peat and humic acid) to sequester iodine from the vapor and aqueous phases. NOM-associated iodine may be stable for geological storage. NOM-sequestered iodine can be recovered by pyrolysis to prepare target materials for transmutation. The nature of the NOM-iodine association has been explored.     

Determination of237Np in large volume samples of sea water by a radiochemical procedure

A radiochemical procedure followed by alpha spectrometry has been developed for the determination of²³⁷Np present at low activity concentrations in seawater. The analytical procedure is based on concentration of actinides from 1800 1 sea water samples by hydroxide precipitations. Neptunium is isolated by ion exchange, fluoride precipitation and extraction with TTA (thenoyltrifluoroacetone). As a radiochemical yield determinant²³⁹Np or²³⁵Np is used. Neptunium is electroplated onto stainless steel discs before alpha-spectrometry for about 10 days. The procedure allows for sequential separation of plutonium, americium, technetium and radiocaesium together with neptunium. The radiochemical yield for neptunium is only 20–50%, but the procedure has been applied with success on several samples contaminated with²³⁷Np at fallout or close to fallout levels.     

Potential of lichens for monitoring iodine-129 and chlorine-36

Chlorine-36 (half life 3.01 × 10⁵ year), a beta emitter, is produced naturally but its presence has been enhanced by atmospheric weapons testing and other nuclear activities. Iodine-129 has a half life of 1.57 × 10⁷ years and is also produced by nuclear activities, in particular fuel reprocessing. Many elements have a long biological half-life in lichens, which were thus investigated so as to assess their suitability for ³⁶Cl and ¹²⁹I monitoring. Lichens sampled between 1998 and 2008 were analysed for total chlorine, and selected samples were processed for ³⁶Cl measurement using Accelerator Mass Spectrometry (AMS); ¹²⁹I was analyzed by gamma spectrometry. Different aspects are discussed: long-term storage in lichens versus environmental mobility, levels in samples collected near a reprocessing facility, and potential for spatial and temporal monitoring.     

Neutron activation and mass spectrometric measurement of129I

An integrated procedure has been developed for measurement of¹²⁹I by neutron activation analysis and mass spectrometry. An iodine isolation procedure previously used for neutron activation has been modified to provide separated iodine suitable for mass spectrometric measurement as well. Agreement between both methods has been achieved within error limits. The measurement limit by each method is about 10⁷ atoms /2 fg/ of¹²⁹I.Operated for the U.S. Department of Energy by Battelle Memorial Institute under contract DE-AC06-76RL0 1830.     

Further study on NAA in characterizations of reference materials

A program was initiated at Chalk River Laboratories (CRL) to determine the physical, chemical and radiological properties of wastes intended for disposal in IRUS (Intrusion Resistant Underground Structure), a below ground vault to be constructed at CRL. One of the most restrictive radionuclides for IRUS is¹²⁹I, which has been assigned a maximum activity concentration in waste of 10⁶ Bq/m³. The limit of detection for radionuclides in waste has been set at 1% of the approximate maximum activity concentration, or 10⁴ Bq/m³ for¹²⁹I. A radiochemical instrumental neutron activation analysis method has been developed to determine¹²⁹I in two waste streams, incinerator ash and liquid feed to a bituminizer. Solid samples are spiked with¹²⁵I tracer, fused at 960°C with Li₂B₄O₇ in a platinum boat in a flowing oxygen stream inside a three zone tube furnace, and the volatilized I₂ is trapped on in-line charcoal filters. The charcoal filters are irradiated together with a filter containing a spiked¹²⁵I/¹²⁹I standard, in the NRU reactor, and then subjected to post-irradiation chemistry to remove⁸²Br interference. The¹²⁹I concentration in the sample is determined by comparing the activity of the activated¹³⁰I in the sample with that of the standard, and the chemical recovery for¹²⁹I is determined from the activity of¹²⁵I tracer. Limits of detection for¹²⁹I in solids are typically 0.005 Bq/g, based on a 4 hour counting period on a 10% efficient HPGe gamma-spectrometer at a source to detector distance of approximately 12 cm. This paper presents a summary of the method and the results from analysis of two waste streams.     

Chemical and nuclear interferences in neutron activation of129I and127I in environmental samples

A combination of neutron activation and gamma-ray coincidence counting technique is used to determine the concentration of both long-lived fission produced¹²⁹I and natural¹²⁷I in environmental samples. The neutron reactions used for the activation of the iodine isotopes are¹²⁹I(n, )¹³⁰I and¹²⁷I(n, 2n)¹²⁶I. Nuclear interferences in the activation analysis of¹²⁹I and¹²⁷I can be caused by production of¹³⁰I or¹²⁶I from other constituents of the materials to be irradiated, i.e. Te, Cs and U impurities and from the¹²⁵I tracer used for chemical yield determination. Chemical interferences can be caused by¹²⁹I and¹²⁷I impurities in the reagents used in the pre-irradiation separation of iodine. The activated charcoals used as iodine absorbers were carefully cleaned. Different chemical forms of added¹²⁵I tracer and¹²⁹I and¹²⁷I constituents of the samples can cause different behaviour of¹²⁵I tracer and sample iodine isotopes during pre-irradiation separation of iodine. The magnitude of the nuclear and chemical interferences has been determined. Procedures have been developed to prevent or control possible interferences in low-level¹²⁹I and¹²⁷I activation analysis. For quality control a number of biological and environmental standard samples were analyzed for¹²⁷I and¹²⁹I concentrations.     

Determination of gaseous and particulate129I in atmospheric air by neutron activation analysis

A method for determining¹²⁹I in atmospheric air is presented. It consists of the following stages: sampling (of aerosol and gas fractions separately), preparation of a sample for irradiation in a reactor by a destructive distillation method, irradiation of samples in a reactor, radiochemical separation and¹³⁰I activity measurements by slow coincidences. Iodine isotopes (including¹²⁹I) in the atmospheric air have mostly been found in gas fractions (except¹³²I). Gas compounds and percentages of radioactive and stable iodine isotopes coincide.Presented at the MTAA-8 Conference, September 16–20, 1991, Vienna, Austria.     

Iodine-129 in Thyroid Glands: A Sensitive Biological Marker of Fission Product Exposure

Iodine-129 may have no radiation hazard but it is a useful marker. Animal thyroids concentrate the isotope to 4 orders of magnitude greater than the intake. This results in a potential biological and physical indicator of radioiodine contamination. Since 1943, ¹²⁹I/¹²⁷I ratio in animal thyroids from the Northern Hemisphere has increased 2 to 5 orders of magnitude. Since 1985, thyroids of deer living near a nuclear reprocessing facility have contained ¹²⁹I, which are 3 to 7 orders of magnitude greater than pre-nuclear levels. Limited measurements of ¹²⁹I in thyroids from the Southern Hemisphere have shown little increase. An appendix is presented to show that ¹²⁹I, may be helpful to evaluate past radiation hazard from fission products.     

Determination of iodine in biological materials by neutron activation analysis

A method of determination of iodine (total and PBI) in serum, urine and other biological materials has been developed. The method consists in a gamma-spectrometric measurement of¹²⁸I activity after its radiochemical separation. The radiochemical separation procedure includes wet decomposition of the samples in a nitric acid medium followed by a few separation steps, the essential step being the substoichiometric extraction of iodide with a chloroform solution of tetraphenylarsonium chloride. Owing to the application of the substoichiometric separation, a high radiochemical purity of the separated iodine is achieved and the determination of the yield of radiochemical separation is not necessary.     

A review on speciation of iodine-129 in the environmental and biological samples

As a long-lived beta-emitting radioisotope of iodine, ¹²⁹I is produced both naturally and as a result of human nuclear activities. At present time, the main part of ¹²⁹I in the environment originates from the human nuclear activity, especially the releases from the spent nuclear fuel reprocessing plants, the ¹²⁹I/¹²⁷I ratios have being reached to values of 10⁻¹⁰ to 10⁻⁴ in the environment from 10⁻¹² in the pre-nuclear era. In this article, we review the occurrence, sources, inventory, and concentration level of ¹²⁹I in environment and the method for speciation analysis of ¹²⁹I in the environment. Measurement techniques for the determination of ¹²⁹I are presented and compared. An overview of applications of ¹²⁹I speciation in various scientific disciplines such as radiation protection, waste depository, and environmental sciences is given. In addition, the bioavailability and radiation toxicity (dose to thyroid) of ¹²⁹I are discussed.