An episode of Ru-106 in air over Europe, September-October 2017 - Geographical distribution of inhalation dose over Europe.

Between the end of September and early October 2017, 106Ru was recorded by air monitoring stations across parts of Europe. In the environment, this purely anthropogenic radionuclide can be detected very rarely only. As far as known, 106Ru is only used in radiotherapy and possibly in radiothermal generators. Therefore, the episode drew considerable interest in the monitoring community, although the activity concentrations and resulting exposure were far below radiological concern. Health consequences can be practically excluded except possibly near the source. 106Ru in aerosols could be detected for several weeks and in some regions of Central and Eastern Europe tens, up to over 100 mBq/m³ were measured as one-day means. Discussions about a possible source continue until today (early 2019). Atmospheric back-modelling led to trajectories likely originating in the Southern to Northern Ural region of Russia and possibly Northern Kazakhstan. Suspiciously, no other anthropogenic radionuclides have been observed alongside, except minute concentrations of comparatively short-lived 103Ru (half life 39 d vs. 376 d for 106Ru). Due to the absence of other anthropogenic radionuclides, a reactor accident can be excluded, although both Ru isotopes are fission products generated in nuclear reactors. The exposure resulting from 106Ru activity concentration in air exceeded 200 mBq × d/m³ in some parts of Central and Eastern Europe. This leads to inhalation doses of up to about 0.3 µSv regionally, assuming the radiologically most efficient speciation, lacking better information, and inhalation dose conversion factors from ICRP 119. We show an interpolated map of the dose distribution over parts of Europe where sufficient measurements are available to us. Overlaying population density, we give an estimate of collective dose. The opportunity is also used to give a short review of origin, properties and use of 106Ru, as well as of accidents which involved release of this radionuclide.

The work programme of NERIS in post-accident recovery.

NERIS is the European platform on preparedness for nuclear and radiological emergency response and recovery. Created in 2010 with 57 organisations from 28 different countries, the objectives of the platform are to: improve the effectiveness and coherency of current approaches to preparedness; identify further development needs; improve 'know how' and technical expertise; and establish a forum for dialogue and methodological development. The NERIS Strategic Research Agenda is now structured with three main challenges: (i) radiological impact assessments during all phases of nuclear and radiological events; (ii) countermeasures and countermeasure strategies in emergency and recovery, decision support, and disaster informatics; and (iii) setting up a multi-faceted framework for preparedness for emergency response and recovery. The Fukushima accident has highlighted some key issues for further consideration in NERIS research activities, including: the importance of transparency of decision-making processes at local, regional, and national levels; the key role of access to environmental monitoring; the importance of dealing with uncertainties in assessment and management of the different phases of the accident; the use of modern social media in the exchange of information; the role of stakeholder involvement processes in both emergency and recovery situations; considerations of societal, ethical, and economic aspects; and the reinforcement of education and training for various actors. This paper emphasises the main issues at stake for NERIS for post-accident management.

Potential consequences of the Fukushima accident for off-site nuclear emergency management: a case study for Germany.

The Fukushima accident led to high radionuclide releases into the atmosphere for more than 3 weeks. This situation has not been assumed when the concepts of nuclear emergency preparedness were developed internationally. The results of simulations studying potential implications of Fukushima-like source terms on nuclear emergency preparedness are presented. Two hypothetical source terms are considered. Radiological consequences are assessed with the decision support system RODOS. Atmospheric dispersion calculations are based on meteorological monitoring data from June and December 2010, respectively, to study potential seasonal effects. Simulations are performed for two nuclear power plant sites in Northern and Southern Germany, respectively. These sites are chosen due to their differing meteorology and topography. Predicted radiation doses of members of the population are compared with dose reference levels actually recommended for initiating protective measures in Germany. Potential implications of general interest for nuclear emergency planning are discussed.

Comparative study of Dutch and German emergency-management models for near border nuclear accidents.

Four institutes, all of which are involved in nuclear-emergency management in the Dutch-German border region, have compared their short-range dispersion and radiological dose models using scenarios consisting of single-station meteorology and two dispersed radionuclides. After adjustment of some of the parameters, the consequence of the differences in parameters on the effective dose was quantified at several stages from source to exposure. Results for the neutral stability class agreed within a factor of four. Variations in wet deposition of radioactive material, giving rise to external radiation from the ground, can cause significant variations to the effective dose. Furthermore, the way the different emergency-management tools model the atmospheric dispersion for a stable stability class in the horizontal plane can generate large differences. Finally, the methodology of calculating cloudshine is not comparable among the models, which causes the effective dose near the source to show large deviations for high emission sources.

Data assimilation in the decision support system rodos.

Model predictions for a rapid assessment and prognosis of possible radiological consequences after an accidental release of radionuclides play an important role in nuclear emergency management. Radiological observations, e.g. dose rate measurements, can be used to improve such model predictions. The process of combining model predictions and observations, usually referred to as data assimilation, is described in this article within the framework of the real time on-line decision support system (RODOS) for off-site nuclear emergency management in Europe. Data assimilation capabilities, based on Kalman filters, are under development for several modules of the RODOS system, including the atmospheric dispersion, deposition, food chain and hydrological models. The use of such a generic data assimilation methodology enables the propagation of uncertainties throughout the various modules of the system. This would in turn provide decision makers with uncertainty estimates taking into account both model and observation errors. This paper describes the methodology employed as well as results of some preliminary studies based on simulated data.

In situ gamma-ray spectrometry in forests: determination of kerma rate in air from 137Cs.

A method is presented to determine the kerma rate in air from 137Cs due to Chernobyl fallout in forests. In situ gamma-ray spectra from several forest sites in Russia, in the Ukraine and in Southern Germany are evaluated with the aim of deducing the ratio of primary and forward scattered photons for 137Cs. With this ratio and the results of Monte-Carlo simulations of photon transport the contribution of scattered photons to the total kerma is assessed successfully. Scattered photons contribute between 42% and 50% to the total kerma rate from radiocesium, which is less than according values for grassland areas. The contribution of radiocesium to the total kerma rate varies between 40% and 90%. whereas radiocesium stored in the forest biomass contributes only a few percent. The mean mass depth of radiocesium ranges from 2.6 to 6.4 g cm(-2) in the forest soils.

Thyroid cancer risk in Belarus after the Chernobyl accident: comparison with external exposures.

Within the time period 1990-1993, childhood thyroid cancer incidence due to the Chernobyl accident increased dramatically in Belarus, especially with regard to the birth cohort January 1, 1971, to May 31, 1986. This rise subsequently slowed down, i.e. during the period 1994-1996. The respective data were analysed and compared with the results of an analysis on the time dependence of thyroid cancer incidence in a pooled cohort of persons who had been exposed during childhood to external radiation with high dose rates. Concerning the period of 5-10 years following exposure, the excess absolute cancer risk per unit thyroid dose in the latter (external) exposure group was found to exceed the one in the Belarus group by a factor of two. This difference, however, is not statistically significant. The age-adjusted average excess absolute risk per unit thyroid dose for the period of 5-50 years following external childhood exposure was found to be 8 female and 14 male cases per 10(4) person-year Gy, which is a factor about 2.5 times higher than for the non-adjusted risk in the pooled cohort, as reported by Ron et al. in 1995. Assessments of future excess thyroid cancer cases due to the Chernobyl accident were done on the basis of the time dependence of thyroid cancer risk following external exposure. The thyroid cancer incidence among the birth cohort considered in Belarus and for a period starting from the cessation of the available observation data (1 January 1997) and extending to 50 years after the Chernobyl accident has been estimated to be about 15,000 cases, with an uncertainty range of 5,000-45,000 cases. According to our calculations, 80% of these cases exceed the baseline risk under enhanced thyroid surveillance.

In situ gamma-spectrometry several years after deposition of radiocesium. II. Peak-to-valley method.

A new method is introduced for deriving radiocesium soil contaminations and kerma rates in air from in situ gamma-ray spectrometric measurements. The approach makes use of additional information about gamma-ray attenuation given by the peak-to-valley ratio, which is the ratio of the count rates for primary and forward scattered photons. In situ measurements are evaluated by comparing the experimental data with the results of Monte Carlo simulations of photon transport and detector response. The influence of photons emitted by natural radionuclides on the calculation of the peak-to-valley ratio is carefully analysed. The new method has been applied to several post-Chernobyl measurements and the results agreed well with those of soil sampling.