ESTIMATION OF AIRBORNE 106RU ACTIVITY CONCENTRATION FROM TOTAL BETA ACTIVITY OF PM10 PARTICLE FRACTIONS

Airborne radioruthenium, as a result of an accidental release, presents a risk for occupational and public exposure. In fall 2017, a detection of 106Ru was reported by the European atmospheric radioactive contamination monitoring networks. We investigated the daily specific total beta activity of PM10 particle fractions samples. The presented method enables indirect determination of airborne 106Ru activity concentration from total beta activity, in case 106Ru was confirmed as single excess radiological pollutant. This allows for daily measurements and time-resolved 106Ru activity concentration data. We estimated the indicative committed effective dose due to 106Ru inhalation for the Croatian population during the exposure period. Although the estimated dose value of ~169.7 nSv, for ~6-d duration of ruthenium air pollution, was very low, it was ~40 times higher than the value for Hinh from inhalation of other radionuclides (90Sr + 137Cs + 40K + 7Be).

MEASUREMENT OF OPERATIONAL QUANTITIES Hp(0.07) AND Hp(3) FOR INDIGENOUSLY DEVELOPED 106Ru/106Rh SOURCE USING AN EXTRAPOLATION CHAMBER

In the present study, a prototype 106Ru/106Rh source was fabricated using high level liquid waste from reactor fuel, fixed in a stainless steel housing with a window and backing made of silver. The study involves measurement of the operational quantities Hp(0.07), Hp(3) and the percentage depth dose (PDD) using an extrapolation chamber. It also involves determination of necessary correction factors to arrive at Hp(0.07) and Hp(3) following International Organisation for Standardisation (ISO) and methods suggested in literature. The study facilitates incorporation of the 106Ru/106Rh source as a beta reference source for quality assurance programme in TLD personnel monitoring as per the guidelines of ISO.

Cytogenetic Analysis After Temporary Residence in the Area of the Uncontrolled Ruthenium-106 Release in Russia in September 2017

In September and October 2017, elevated atmospheric ruthenium contamination was measured in several European countries. The most probable origin of this release of radionuclides was reconstructed to be the Southern Ural region. During that time, five workers from a German company stayed up to 2 wk about 120 km from the Chelyabinsk region in Ekaterinburg, Russia. No clinical symptoms were reported during or after the suspected radiation exposure, and no internal contamination was found in whole-body measurements. However, to investigate radiation protection issues and to clarify the workers' situation in order to reassure them, as they planned to continue working in Ekaterinburg, our laboratory was urgently requested by the company's occupational physician to perform biodosimetry using dicentric analysis to determine if the workers have been exposed to radiation by incorporation of radionuclides. The workers' dicentric yields have been compared to reference data of background frequencies in unexposed individuals, but, as it is not reasonable to quantify individual absorbed radiation doses from internalized beta emitters due to various confounding factors, individual dose estimation has not been performed. Dicentric frequencies for two workers differed significantly from the mean laboratory background level, which could have been induced by an exposure to incorporated radionuclides due to beta emissions by Ru or to gamma irradiation by the decay nuclide of Ru. However, the maximum absorbed radiation doses calculated for a resident in the Ru-contaminated area during that time does not correspond to the observed dicentric frequencies. It cannot be excluded that their dicentric frequencies were already elevated before September 2017, potentially induced by an earlier radiation exposure to diagnostic x rays or even by chance.

Evaluation of Hungarian monitoring results and source localization of the 106Ru release in the fall of 2017

Anthropogenic ¹⁰⁶Ru has been detected in the environment from late September to early October 2017 by several European environmental radiological monitoring networks. The paper presents the comprehensive evaluation of Hungarian monitoring results related to the occurrence of ¹⁰⁶Ru in various environmental compartments (airborne particulates, deposition, plants, and terrestrial indicators), which was implemented to determine the temporal and spatial variation of the contaminant on a national scale and also to verify the findings based on the data arising from environmental monitoring at a local scale in Budapest. Difficulties in direct comparison of the diverse reported data were also considered; results arising from varied sampling periods were corrected with account taken of the relation between the sampling duration and 4-day-long plume residence (estimation based on the daily monitoring of air and backward trajectory analysis). Integrated analysis of air and deposition measurements and meteorological data was also performed; the deposition processes were investigated by establishing the correlations of activity concentrations measured in the atmosphere and in the deposition samples. In order to study the temporal distribution and spatial localization of the ¹⁰⁶Ru contamination and to interpret the measurements at ground level, backward trajectory analysis was performed with HYSPLIT model. The backward trajectory simulations suggested that the release had probably occurred during the last week of September 2017 from the geographical area between Volga and the Urals. In addition, assessment of the doses due to the ¹⁰⁶Ru release was implemented considering external exposure from cloudshine and groundshine and internal exposure via inhalation.

Method for source localization proposed and applied to the October 2017 case of atmospheric dispersion of Ru-106

An efficient numerical method for the temporal and spatial localization of an unknown point source of an atmospheric tracer is proposed. The method, which is based on inverse modelling techniques, employs available data from a network of ground-level stations on the condition that the measurements represent the plume geographically and temporally. The method, which employs a level-of-agreement approach, is applied to the October 2017 air concentration measurements of Ru-106 in Europe.

The biokinetics of ruthenium in the human body

The International Commission on Radiological Protection (ICRP) is updating its biokinetic and dosimetric models for workers and subsequently will revisit its models for members of the public. This paper summarises the biokinetic database for ruthenium and proposes a new biokinetic model for systemic ruthenium. In contrast to the ICRP's current model, the proposed model depicts recycling of ruthenium between tissues and blood and a non-uniform distribution of systemic ruthenium. The paper also points out inconsistencies between the ICRP's respiratory model for RuO(4) vapour and reported data, and inconsistencies between the ICRP's default gastrointestinal (GI) uptake value and data for some forms of ruthenium. Dosimetric implications of the proposed systemic model and the findings for inhaled RuO(4) vapour and GI uptake of ruthenium are examined.

Comparison of measured and calculated spatial dose distributions for a bench-mark 106Ru/106Rh hot particle source

This study is a part of a programme of research to provide validated dose measurement and calculation techniques for beta emitting hot particles by the construction of well-defined model hot particle sources. This enables parallel measurements and calculations to be critically compared. This particular study concentrates on the high-energy beta emitter, (106)Ru/(106)Rh (Emax = 3.54 MeV). This source is a common constituent of failed nuclear fuel, particularly in accident situations. The depth dose distributions were measured using radiochromic dye film (RDF); an imaging photon detector coupled to an LiF thermoluminescent dosemeter (LiF-IPD) and an extrapolation ionisation chamber (ECH). Dose calculations were performed using the Monte Carlo radiation transport code MCNP4C. Doses were measured and calculated as average values over various areas and depths. Of particular interest are the doses at depths of 7 and 30-50 mg cm(-2), and averaged over an area of 1 cm2, as recommended by the International Commission on Radiological Protection for use in routine and accidental over-exposures of the skin. In this case, the average ratios (MCNP/measurement) for RDF, ECH and LiF-IPD were 1.07 +/- 0.02, 1.02 +/- 0.01 and 0.83 +/- 0.16, respectively. There are significantly greater discrepancies between the ECH and LiF-IPD measurement techniques and calculations-particularly for shallow depths and small averaging areas.

High-precision Ru isotopic measurements by multi-collector ICP-MS

Ruthenium isotopic data for a pure Aldrich ruthenium nitrate solution obtained using a Nu Plasma multi collector inductively coupled plasma-mass spectrometer (MC-ICP-MS) shows excellent agreement (better than 1 epsilon unit = 1 part in 10(4)) with data obtained by other techniques for the mass range between 96 and 101 amu. External precisions are at the 0.5-1.7 epsilon level (2sigma). Higher sensitivity for MC ICP-MS compared to negative thermal ionization mass spectrometry (N-TIMS) is offset by the uncertainties introduced by relatively large mass discrimination and instabilities in the plasma source-ion extraction region that affect the long-term reproducibility. Large mass bias correction in ICP mass spectrometry demands particular attention to be paid to the choice of normalizing isotopes. Because of its position in the mass spectrum and the large mass bias correction, obtaining precise and accurate abundance data for 104Ru by MC-ICP-MS remains difficult. Internal and external mass bias correction schemes in this mass range may show similar shortcomings if the isotope of interest does not lie within the mass range covered by the masses used for normalization. Analyses of meteorite samples show that if isobaric interferences from Mo are sufficiently large (Ru/Mo < 10(4)), uncertainties on the Mo interference correction propagate through the mass bias correction and yield inaccurate results for Ru isotopic compositions. Second-order linear corrections may be used to correct for these inaccuracies, but such results are generally less precise than N-TIMS data.

Distribution of organic carbon, selected stable elements and artificial radionuclides among dissolved, colloidal and particulate phases in the Rhône River (France): preliminary results

The behaviour of radionuclides discharged from nuclear facilities in the Rhône River depends on their distribution among the dissolved, colloidal and particulate phases. A large water sample was fractionated using sequential ultrafiltration. Size distributions of organic carbon, Fe, Al, Si, Ca, Mg, Cu, Zn, 137Cs, 60Co and 106Ru were obtained. Our results show that organic colloids account for 11% of the total organic carbon content. Approximately 20% of the dissolved (< 450 nm) Fe and Al are in colloidal classes. 137Cs is not significantly transferred by the colloidal phase while 25% of 60Co or 106Ru is associated with organic and inorganic colloids.

Dynamic modeling of the cesium, strontium and ruthenium transfer to grass and vegetables

From 1988 to 1993, the Nuclear Safety and Protection Institute (Institut de Protection et de Sûreté Nucléaire--IPSN) conducted experimental programs focused on transfers to vegetation following accidental localized deposits of radioactive aerosols. In relation to vegetable crops (fruit, leaves, and root vegetables) and meadow grass these experiments have enabled a determination of the factors involved in the transfer of cesium, strontium, and ruthenium at successive harvests, or cuttings, in respect of various time lags after contamination. The dynamic modeling given by these results allows an evaluation of changes in the mass activity of vegetables and grass during the months following deposit. It constitutes part of the ASTRAL post-accident radioecology model.

Measurement of resuspended aerosol in the Chernobyl area. Part II. Size distribution of radioactive particles

Size distribution measurements of particulate radionuclides were performed at two sites in the Chernobyl 30-km exclusion zone using several cascade impactors. The results obtained in the period September 1986 till June 1993 were discussed with regard to the general assumption of a log-normal activity size distribution in inhalation dose assessment. At Zapolie (a site 14 km from the Chernobyl reactor) a bimodal distribution was observed in 91% of all measured distributions. In most cases the medians were about 4 microns and in the range 20-30 microns. According to soil granulometric data this finding was explained by superimposing two processes: local resuspension and advective transport of radioactive aerosol from highly contaminated territories. The mean air concentration showed an increasing proportion of inhalable particles over the years since the accident. In 1993 the inhalable fraction was about 48% of the total concentration. At Pripyat, a site situated within a highly contaminated area, unimodal types of size distributions were predominant with the median diameters in the range 5-10 microns for 137Cs. For the three nuclides 137Cs, 144Ce and 106Ru, very similar types of distribution were observed. Apparently, the radioactive aerosol was of fuel origin. During a forest fire at a distance of 17 km, the majority of the radioactivity was associated with submicrometer particles with median diameters in the range 0.28-0.50 micron.

Direct determination of 90Sr and 147Pm in Chernobyl hot particles collected in Kiev using beta absorption method

59 hot particles were collected in Kiev, Ukraine, in 1987. All but one were prepared from a moss carpet of 360 cm2 area. Radionuclide composition of the hot particles was investigated by gamma-spectrometry and beta absorption method. Pure beta emitters 90Sr and 147Pm were determined in 25 hot particles measuring the beta absorption curves of the hot particles with an end-window Geiger-Müller counter and decomposing the curves in order to obtain the contributions of 90Sr and 147Pm to the total beta counting rate. All but one of the hot particles were found to be the debris of the fuel. The activity ratio 90Sr:l44Ce was 0.052 in good agreement with theoretical calculations on core inventories. This means that strontium behaved as a nonvolatile element in the process of the formation of the hot particles investigated. The activity ratio 147Pm:144Ce was 0.078 which is half of the theoretical result. Although 147Pm is considered to be a refractory nuclide, it seems that significant part of 147Pm went to the homogeneous fraction of the general fallout. The surface density of hot particles (of higher than about 50 Bq activity) was about 1,600 m(-2) and that of the activities of the nuclides 90Sr, 106Ru, 134Cs, 137Cs, 144Ce and 147Pm as components of hot particles was 12.2, 54.3, 5.9, 9.7, 234 and 18.3 kBq m(-2) (activity values counted for 26 April 1986), respectively, in downtown Kiev city in 1987.

The determination of low levels of radiocaesium and radioruthenium in foodstuffs

The Ministry of Agriculture, Fisheries and Food (MAFF) has the responsibility for safeguarding the food supply from authorised and accidental releases of radioactivity to the environment. MAFF funds a radiological research programme to assist in the achievement of its objectives and has recognised that there is a continuing requirement to develop cost effective and sensitive analytical methods for the detection of very low levels of radioactivity in foodstuffs. High resolution gamma spectrometry is often the most appropriate analytical method for the determination of 103Ru, 106Ru, 134Cs and 137Cs but the detection limits for these radionuclides in bulk foodstuffs do not permit the acquisition of accurate data at very low levels. Beta counting techniques offer inherently higher sensitivities but the development of radiochemical separation techniques is essential to provide appropriate counting sources. A radiochemical separation method has been developed for the determination of radiocaesium and radioruthenium in 0.5 kg fresh wt samples of a variety of foodstuffs. The method was shown to be robust and specific and mean method recoveries of 75% were obtained for both radiocaesium and radioruthenium. MDA's for the 1000 min counts on a gas-flow proportional counter were determined to be 0.015 Bq/kg fresh wt for both 137Cs and 106Ru.

Vertical radionuclide transfer by infiltration water in forest soils in the 30-km Chernobyl accident zone

Vertical intrasoil flow within the 30-km zone of the Chernobyl nuclear power plant (ChNPP) was investigated by a lysimetric method in 1989-1990. The regularity of radionuclide migration within the flow has been found to be dependent on the contamination density, the type of radionuclide, and the type of ecosystem and depth.

Radionuclides in the liquid phase of the forest soils at the Chernobyl accident zone

The relative content (alpha) of 137Cs (1987-1991), 106Ru, 134Cs, 144Ce (1987) and the chemical speciation of radionuclides in the liquid phase of forest soils at different plots in the 30-km Chernobyl zone were studied. One year after the accident, substantial variations in the alpha-value between the different plots and a variation in alpha along the soil profile were observed due to unequal physico-chemical properties of nuclear fallout and soils. The alpha-value calculated for the total contaminated layer (alpha av) at different plots varied within relatively narrow limits. Between 77 and 97% of 137Cs in soil solution was shown to be included in organic compounds (MMw, 10(2)-10(4) Da), the latter making a major contribution to the radionuclide transport from soil to plant. The alpha-value for 137Cs for all plots in the Chernobyl 30-km zone and the differences in alpha value between plots had a tendency to decrease with time. These data indicate that the process of 137Cs fixation by the soil solid phase was prevalent. Now, the 'soil-soil solution' system is approaching equilibrium for the radionuclide distribution between solid and liquid phases.

Profiles and downward migration of 134Cs and 106Ru deposited on Italian soils after the Chernobyl accident

After the Chernobyl accident, several radionuclides were deposited on the soil of the Piemonte Region in Italy. Contamination values were monitored and the initial vertical soil profiles of 134Cs and 106Ru were determined. For both radionuclides, more than 60% of the total activity remained in the upper 1-cm layer of soil during the first 7 mo after the accident. The time history of the soil profiles was studied over a period of 3 y in two Piedmontese localities. A compartmental model was also developed to describe downward migration of 134Cs and 106Ru. The results indicated a low mobility for both radionuclides. The change in their vertical profiles may be described using a box model with a transfer constant of 0.2 y-1 for 134Cs and 0.3 y-1 for 106Ru between 1-cm-thick layers. A strong association between the soil fine fraction and the mobility of both radionuclides was also found.

Relationships between deposition of Chernobyl originating caesium and ruthenium radionuclides and rainfall in Ireland

Deposition data for caesium and ruthenium radionuclides in Ireland as a result of the Chernobyl accident were obtained by high-resolution gamma-ray spectrometry of soil samples taken at 111 locations throughout the country. Investigation of the relationships between deposition and recorded rainfall in relevant periods enabled an assessment to be made of the activity concentration within the plume during the wash-out phase. Detailed surveys in two regions of the country enabled a comparison to be made of the relative deposition of ruthenium and caesium isotopes. No evidence was found to suggest any difference in wash-out ratios for the two ruthenium isotopes.

Interception and retention of Chernobyl-derived 134Cs, 137Cs and 106Ru in a spruce stand

The time dependence of the specific activity of Chernobyl-derived 134Cs, 137Cs and 106Ru was determined in vegetation and soil samples from an old spruce stand within a period of 600 days after the beginning of the radioactive fallout. The results show that 70% of the total activity of radiocesium and 60% of radioruthenium deposited in the spruce stand were retained initially in the canopy. They were removed from the needles and twigs as a result of weathering (rain, wind, litter fall) and transferred to the forest floor, but only rather slowly (half-lives in the canopy: radiocesium, 90 days for the period 0-130 days, 230 days for the period 130-600 days; radioruthenium, 95 days for the period 0-200 days). The transfer of radiocesium and ruthenium to the forest floor by litter-fall was small when compared with that of weathering by rain or wind (radiocesium 7%, radioruthenium 8%, with respect to the total activity deposited in the canopy). The total deposition of radiocesium and ruthenium in the spruce stand was higher by 20 and 24%, respectively, than that observed in nearby grassland. The deposition velocity of radiocesium in the spruce stand was estimated at 5.5 mm s-1, higher by a factor of 10 than the figure for grassland. Similar values were found for radioruthenium.