Kasper Grann Andersson

Iodine-129 and Caesium-137 in Chernobyl contaminated soil and their chemical fractionation

Soil samples from areas in Belarus, Russia and Sweden contaminated by the Chernobyl accident were analysed for (129)I by radiochemical neutron activation analysis, as well as for 137Cs by gamma-spectrometry. The atomic ratio of (129)I/137Cs in the upper layer of the examined soil cores ranged from 0.10 to 0.30, with an average of 0.18, and no correlation between (129)I/137Cs ratio and the distance from Chernobyl reactor to sampling location was observed. It seems feasible to use the (129)I/137Cs ratio to reconstruct the deposition pattern of 131I in these areas. The association of (129)I and 137Cs in the Chernobyl soil and Irish Sea sediment was investigated by a sequential extraction method. Similar speciation of (129)I in the Chernobyl soil and Irish Sea sediment was found. Approximately 70% of (129)I is bound to oxides and organic matter, and 10-20% is in the readily available phase, while most of the 137Cs (73%) in Chernobyl soil remains in the extraction residue.

The behaviour of Chernobyl 137Cs, 134Cs and 106Ru in undisturbed soil: implications for external radiation

Following the Chernobyl accident, deposits of 137Cs, 134Cs and 106Ru on exposed surfaces in urban areas were found to be the major contributors to the external radiation dose. The fixation of these radionuclides in soils was investigated by the determination of their vertical distribution in and through sequential extractions. Four years after the Chernobyl accident it was found that most of the caesium remained firmly fixed in the topmost 2 cm. In the deeper layers of the soil it was less strongly bound. The ruthenium was found to be less strongly bound than the caesium and had penetrated a little deeper. The study indicates the need for countermeasures if the long-term deeper. The study indicates the need for countermeasures if the long-term radiation dose to the local populace is to be reduced significantly

Weathering of radiocaesium contamination on urban streets, walls and roofs

Recent investigations in Russia have emphasised the significance of dose contributions from contamination on urban streets and roof pavings, and, typically to a lesser extent, walls in the urban environment. The crucial factor determining the magnitude of these contributions is the retention of the contamination by the different types of urban surface. Since the Chernobyl accident, a series of long-term field studies has been carried out on urban streets, walls and roofs, to examine the weathering processes of 137Cs on the various surface types. The derived time-functions are applied to estimate resultant long-term doses to inhabitants of an urban centre. The paper highlights the effect on caesium retention of surface material characteristics.

Radiation dose implications of airborne contaminant deposition to humans

Abstract— In nuclear accident consequence assessment, dose contributions from radionuclide deposition on the human body have in the past generally been either ignored or estimated on the basis of rather simple models. Recent experimental work has improved the state of knowledge of relevant processes and parameter ranges. The results presented in this paper represent a first approach to a detailed assessment of doses from radiopollutant deposition on the human body, based on contaminant-specific data. Both the dose to skin from beta-emitters and the whole-body dose from gamma-emitters on body surfaces were found to give potentially significant contributions to dose. Further, skin penetration of some contaminants could lead to significant internal doses.

Dynamic behaviour of 137Cs contamination in trees of the Briansk region, Russia

Seven trees were felled in the Briansk region in 1997. The trees were sectioned for sampling, both at different heights and according to year rings, and samples were analysed for content of 137Cs. In general, the specific activity of 137Cs was much higher in the fresh parts of the three (needles, leaves and twigs) than in the core wood. The year ring study showed that 137Cs had penetrated deeply in to the trunk, and no peak was detectable in the year ring corresponding to the Chernobyl accident in 1986. The specific activity in the trunk wood had a maximum at the height corresponding to the growth years at approximately 1986. Neutron activation analysis was used to analyse for stable Cs. The results showed that the relationship between concentrations of 137Cs and stable caesium is much higher in the newer parts of growing trees than in the older parts. Together with a tendency of inward migration this leads to a preliminary conclusion that the 137Cs activity will continue to accumulate in the core wood.

Decontamination in a Russian settlement

Decontamination was carried out in an area with three houses in Novo Bobovichi, Bryansk region, Russia, in the autumn of 1995. It was demonstrated that significant reductions in the dose rate both indoor (DRF = 0.34) and outdoor (DRF = 0.20) can be achieved when a controlled cleaning is undertaken. This paper describes the decontamination work carried out and the results obtained. The roofs of the houses were swept and cleaned by special roof cleaning equipment. The soil around the houses was removed by hand while carefully monitoring the ground for residual contamination. By monitoring the decline in the dose rate during the different stages of the work the dose reducing effect of each action has been measured.

An assessment of cumulative external doses from Chernobyl fallout for a forested area in Russia using the optically stimulated luminescence from quartz inclusions in bricks

Optically stimulated luminescence (OSL) has been used for estimation of the accumulated doses in quartz inclusions obtained from two fired bricks, extracted in July 2004 from a building located in the forested surroundings of the recreational area Novie Bobovichi, the Bryansk Region, Russia. The area was significantly contaminated by Chernobyl fallout with initial (137)Cs ground deposition level of approximately 1.1 MBq m(-2). The accumulated OSL doses in sections of the bricks varied from 141 to 207 mGy, of which between 76 and 146 mGy are attributable to Chernobyl fallout. Using the OSL depth-dose profiles obtained from the exposed bricks and the results from a gamma-ray-survey of the area, the Chernobyl-related cumulative gamma-ray dose for a point detector located in free air at a height of 1m above the ground in the study area was estimated to be ca. 240 mGy for the time period starting on 27 April 1986 and ending on 31 July 2004. This result is in good agreement with the result of deterministic modelling of the cumulative gamma-ray dose in free air above undisturbed ground from the Chernobyl source in the Bryansk Region. Over the same time period, the external Chernobyl-related dose via forest pathway for the most exposed individuals (e.g., forest workers) is estimated to be approximately 39 mSv. Prognosis for the external exposure from 1986 to 2056 is presented and compared with the predictions given by other investigators of the region.

Removal of radioactive fallout from surface of soil and grassed surfaces using peelable coatings

Abstract In the wake of the Chernobyl accident it was found that the greatest contribution to the dose rate in the urban environment came from isotopes of radiocaesium deposited in open areas such as gardens and parks. Without intervention, the contamination would remain on or close to the soil surface for many decades. The efficiency and cost-effectiveness of peelable coatings as a means for removing the contamination was investigated. From small-scale tests it was found that peelable coatings based on polyvinyl alcohol and lignin were effective and inexpensive, both removing more than 90% of the contamination from dry soil.

A Nordic preparedness guide for early clean-up in radioactively contaminated residential areas

Abstract Experience gained from environmental radiological measurements, experimentation and modelling over the past decade has been applied in the development of a Nordic emergency preparedness catalogue which can be used to overview the cost–benefit aspects of an early implementation of measures to reduce long-term external radiation doses to people living in a contaminated residential complex. The catalogue contains information on the dose-reductive effect of a number of actions which are thought to be particularly well suited for the task. The requirements, restrictions, implications and cost elements of each method are listed in a format which is easy to use in a comparative analysis. The data show that if action is taken soon after an accident, it is often possible at relatively little cost to reduce the lifetime external dose to inhabitants of a contaminated area by a factor of 10. The use of the catalogue is discussed in relation to internationally applied intervention levels and concepts as well as to non-radiological aspects.

The skim and burial plough : A new implement for reclamation of radioactively contaminated land

Abstract Radionuclides accidentally released to the atmosphere in severe nuclear accidents can give rise to widespread radioactive contamination of land. If no remedial action is taken, the contamination may constitute a long-term external radiation hazard. Similarly, agricultural and dairy produce from the contaminated land may be a source of internal radiation. A newly developed agricultural implement named the ‘kim and burial’ plough has been built and tested and shown to be an effective countermeasure against both of these potential hazards but without the disadvantages of some other land reclamation methods. The new plough skims off a shallow layer of the contaminated top soil and buries it at a depth of about 45 cm without inverting the 5–45 cm horizon. The results are that radiation levels at the soil surface are greatly reduced, the contamination becomes much less available for plant uptake and in most cases there is little or no effect on soil quality. The efficacy of the new plough has been demonstrated under particularly severe field conditions.