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.

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.

The CONFIDENCE dissemination workshop “Coping with uncertainties for improved modelling and decision making in nuclear emergencies” was held in December 2–5, 2019 (Bratislava, Slovak Republic). About 90 scientists and decision makers attended the workshop. The dissemination workshop allowed the presentation of the CONFIDENCE project results, demonstration of the applicability of the developed methods and tools in interactive discussion sessions and the collection of feedback from the participants. The results were disseminated not only in the form of presentations and posters but also through interactive workshops where all participants were involved in round table working groups. A fictive accidental release scenario taking place at a nuclear power plant was developed and used by each work package in the workshop to provide the basis for interactive sessions and discussions.

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.

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