ISTC Project on Monitoring of Xenon and Krypton Radionuclides in Russia
Yuri Dubasov
The International Science and Technology Center’s (ISTC) Project 2133, or “Development of methodical bases and mobile equipment for monitoring of xenon and krypton radionuclides in the Northwest region of Russia,” was initiated in September 2005 with the author of this article serving as project manager. The research of the Khlopin Radium Institute (KRI) is supported by the Northwest Interregional Administration of Russia’s Federal Service for Hydrometeorology and Environmental Monitoring. The government of Canada provides funding for the project. Foreign collaborators include the Radiation Protection Bureau, Health Canada, the Canadian Meteorological Centre, Environment Canada, the Institute for Atmospheric Radioactivity of the German Federal Office for Radiation Protection (BfS), the Swedish Defense Research Agency (FOI), and the Danish Meteorological Institute.
Xenon and krypton isotopes are formed in large quantities during nuclear fission at nuclear power plants. As they enter the atmosphere easily as a result of their chemical inertness, monitoring xenon and krypton levels is currently a high priority in the field of environmental radiation control.
Knowledge of the concentration and composition of radioactive noble gases (RNG) in the atmosphere makes it possible to determine the nuclear process which resulted in their formation, as well as source characteristics, point of origination, and atmospheric contamination at the sampling point.
The primary goals of the project are the investigation of the atmospheric content of xenon and krypton radionuclides emitted by Northwest Russian nuclear power plants; to study xenon transport; and to elaborate a methodology for RNG monitoring in a given plant’s supervised area. The final objective of the project is the development of mobile equipment and the thorough measurement of RNG levels in the Northwestern region of Russia using this equipment, followed by the interpretation of the data. Data on RNG content in the atmosphere can and must be used to solve some crucial problems of radiation control in the vicinity of nuclear power plants.
There are a significant number of operating plants in Europe, including ten in the European part of the former Soviet Union. Despite all the measures taken to ensure their safe operation, it still does not seem possible to exclude accidents. Therefore, it is crucial to develop regional monitoring systems capable not only of efficiently controlling the radiological impact of nuclear facilities on the environment, but also of tracing contamination back to its point of origin and uncovering the causal mode of operation.
Under standard operation, the measurement of RNG release from nuclear power facilities can be carried out at significant distances (several hundred kilometers) from a nuclear power installation, which enables the mobile laboratories to acquire the relevant data at any time, provided they are downwind of the facility.
The permissible release of radioactive noble gases by nuclear power plants in Russia during normal operation can amount to 500 Ci/day (18,5 x 1012 Bq/day). Some Russian plants already release considerably less. As the main fraction of this radioactivity is accounted for by shortlived isotopes of krypton and xenon, only radionuclides such as 85Kr (T 1/2=10 years) and 131Xe, 133Xe, 133Xe, 135Xe (having half-lives from 2 to10 days) can be spread to significant distances. Since measurement of xenon radionuclides carry substantial difficulties, data on the atmospheric concentration of xenon radionuclides in affected urban areas is largely unavailable.
For control of the activity of nuclear power facilities it is necessary to determine the activities of short-lived RNG isotopes in the air, allowing the timely determination of any emergency occurring at the facility.
The Khlopin Radium Institute possesses significant experience related both to the development of RNG equipment and control methods and to their practical application. In particular, various kinds of noble gas systems (stationary, mobile ship systems, and small van-mounted systems) and methods for the sampling, preparation, and measurement of krypton and xenon radionuclides in background atmospheric samples are developed at KRI. In the 1980s, an experimental network for RNG control was developed on the basis of stationary and mobile units.
Figure 1: Location of several nuclear power plants and control points for ISTC Project 2133 (NPP = nuclear power plant; RNR = rapid neutron reactor)
The successful applications of these developments include the detection of elevated atmospheric RNG levels in such cities as Cherepovets (59,11°N, 37,90°E, Vologda province, Russia), Lipetsk (52,54°N, 39,60°E, Russia), Krivoy Rog (48,00°N, 33,27°E, Ukraine), Enakievo (48,18°N, 38,18°E, Donetsk province, Ukraine) following the Chernobyl accident. The obtained information on 133Xe/133Xe ratios allowed scientists to prove the existence of instant large-scale energy release at the moment of the reactor’s destruction. In Chelyabinsk, increased levels of airborne xenon isotopes were repeatedly recorded: 131Xe, 133Xe, 133Xe, and 135Xe levels were related to releases of industrial reactors.
From 1987 to 1992, more than 1,500 results on the atmospheric 85Kr and 133Xe content in some cities of the former USSR were obtained. The analysis of this information has allowed to identify cities where the average 85Kr and 133Xe content is, to an extent, influenced by the release sources.
The present project will allow a number of tasks connected with the safe operation of industrial nuclear power facilities to be solved. While at present, KRI is the sole Federal Atomic Energy Agency (Rosatom, former Minatom) organization carrying out development and manufacturing of equipment with various weight and dimensional characteristics for RNG measurement at a background level in atmospheric air, a number of well-qualified experts from this project will greatly expand the scope of research in the field.
Observations in the area of St. Petersburg and Cherepovets will allow estimation of the RNG transfer and degree of mutual influence of the Leningradskaya, Kola, and Kalininskaya nuclear plants in Northwestern region control points. For the interpretation of obtained results, regular data exchange on RNG concentrations in observed regions between the Radium Institute and project collaborators will be used.
Three types of measurement systems are to be used in the course of the project execution:
- Mobile installations (RNG automobile laboratory) for xenon and krypton radionuclide activity determination near nuclear power plants; two mobile gas samplers located at distances of five and ten kilometers from the plant during the observation period.
- Installation for sampling of roughly 30~50 m3 air in the middle zone (approximately 100 km from the plant) for observations in St. Petersburg.
- Equipment with high sampling capacity at a greater distance, in Cherepovets.
After the first year of this project, the monitoring equipment manufacturing is nearing completion and the first results of krypton and xenon monitoring have been obtained.
