Origin and Context of the French-German Initiative
The explosion of the RBMK-type reactor No. 4 at the Chernobyl NPP in the Ukraine on April 26, 1986 and the subsequent fire in the core of the reactor led to a considerable release of radioactive substances into the environment as well as to a dispersion of fuel debris in the vicinity of the power plant.
The total radioactivity released into the atmosphere within 10 days amounted to12 exa-Becquerel . The dispersing radioactive cloud spread such radionuclides as iodine 131, caesium 134 and caesium 137 over the majority of the European countries.
In September 1995, several months prior to the signing of the G7 memorandum to support the shutdown of the Chernobyl plant, the Ukrainian Minister of Environmental Protection and Nuclear Safety appealed to all governments for scientific, technical and financial support to create an International Research and Technology Centre for the problems caused by nuclear accidents and irradiation. The main purpose is to resolve the problems resulting from the consequences of the Chernobyl accident.
In response to this appeal the French and German Environmental Ministers jointly announced in Vienna on April 1996, their co-operation initiative with the Ukraine, the Belarus and Russia over scientific projects concerning the aftermath of the Chernobyl disaster.
Three research topics have been specified: the safety of the Sarcophagus, the impact of the accident on the environment (radioecology) and the health of the affected population. In July 1997, the French-German Initiative (FGI) was formalized by the signature of an agreement between IPSN (Institut de Protection et de Sûreté Nucléaire), its German counterpart GRS (Gesellschaft für Anlagen und Reaktorsicherheit) and the CC (Chernobyl Centre).
Aims of the French-German Initiative
In order to establish and guarantee the coherence of short, medium and long-term actions aimed at a better control of the situation after the Chernobyl accident, it was necessary to collect and validate all available knowledge concerning this problem.
The main purpose of the French-German Initiative was to assist in the collection and validation of the existing data for constituting a reliable and objective basis of information useful to the planning of countermeasures, informing the public and for future scientific work.
In the context of this agreement both IRSN and GRS organise methodological support of Ukrainian, Russian and Belarussian organizations to realise scientific projects and set of databases connected with the three above-mentioned research topics.
The access to these informations and results is on www.fgi.icc.gov.ua .
Presentation of Content and Results of the French-German Initiative
1Exa-Becquerel = 1018 Becquerel
2 the group of the most industrially developed countries
3By fusion with OPRI (Office for Protection against Ionising Radiation), IPSN became IRSN (Institut de Radioprotection et de Sûreté Nucléaire) by a law in May9th, 2001 and a decree of February 2nd, 2002.
G. Pretzsch (GRS)4, V. Lhomme (IRSN)5, A. Seleznev6 (CC)
At the Vienna Chernobyl Conference in April 1996 Germany and France declared to support the international co-operation of institutions of the Ukraine, Belarus and Russia in view of a solution of the Chernobyl related issues. After this declaration three project were identified, i.e. the safety state of the Chernobyl Sarcophagus, the radio ecological consequences due to the radioactive contaminated areas and the health consequences of the liquidators and the population in Ukraine, Belarus and Russia after the Chernobyl accident. The projects were funded by the governments and by the electricity utilities of Germany and France, respectively. In this paper the multinational Sarcophagus project launched in 1998 will be presented.
Eighteen years after the accident of Unit 4 of the Chernobyl NPP the Sarcophagus still remains one of the most dangerous nuclear facilities in the world. The ruin of the destroyed Unit 4 and its surrounding Sarcophagus together are termed object Shelter.
The Sarcophagus was erected in a relatively short time period of several months on the basements of old structures of unknown stability of the former unit 4. Inside the Shelter remained about 96 % of the irradiated nuclear fuel inventory of the reactor of unit 4 before the accident, i.e. 180 t of Uranium of total radioactivity 7 x 1017 Bq. The radioactive releases to the industrial site of 500 m radius around the Chernobyl NPP during the first ten days after the accident were estimated to amount 0,5 -1,0% of the fuel inventory.
The spent fuel inside the Shelter and the radioactive contamination at the industrial site have an essential impact on all human activities concerned with investigation work, maintenance and stabilization measures which are presently under progress e.g. in the framework of the Shelter Implementation Plan (SIP) because of the radiation exposure. For planning of any actions towards a stabilization of the unstable building constructions of the Shelter and of measures to retain the radioactive materials inside the Sarcophagus a unified and comprehensive data base of all safety relevant technical data describing the present safety state of the Shelter is required. Hence, the main aim of the Sarcophagus project was the collection, analysis and selection as well as verification of all existing safety relevant data of the Shelter and the creation of an appropriate data base.
The project management was carried out by GRS and IRSN on behalf of the German and French governments and utilities, respectively. The local project co-ordination in Ukraine was carried out by the Chernobyl Centre which was also the beneficiary of the work. The work was performed by local contractors in Ukraine and Russia. The progress of work was frequently estimated and ruled by the project review group from the above mentioned organizations together with the contractors.
During a preparation phase after the declaration of the initiative in 1996 the main tasks of the project were identified and the terms of references including detailed technical specifications of the work were elaborated. These main tasks are Building Constructions, Systems and Equipment, Radiological Situation, Fuel Containing Materials and Radioactive Waste and Environmental Impact. The project duration was planned to be three years, the total budget amounted to 2 Million Euro.
In May 1998 the sub-projects with the local contractors were launched. The technical organization of the project was the following. For each technical task in a first step the main sources of information, i.e. technical documents, publications, data logging protocols etc., were identified and described in a bibliography. In the next steps the technical quantities of interest were extracted from theses documents and put into a data base. The input of data was performed by the contractors using especially designed interfaces, which address the kind and the total amount of data for the given task.
The development of interfaces, the structure and the configuration of the data base as well as the data integration was subject to a separate contract. This work was performed by ECOMM, Kiev, which is the main ESRI distributor for Ukraine. Besides internal quality control of the technical data, performed by each of the contractors, additionally an independent expert team of Atomaudit (AA), Kiev, was involved in external quality control of the work. The configuration of the data base and data integration was also subject to independent control by a GRS supervisor.
CONTENTS OF WORK
1.1 Building Constructions
The content of this work was the description of the building constructions before and after the accident. To the construction parameters considered in this task belong the geometrical dimensions of the rooms, of the walls and of special objects, their properties, e.g. quality of concrete and other building materials, load bearing capacity, order of destruction of walls and other construction elements, newly filled concrete and accessibility of rooms, etc. These data serve as a basis for new projects to reinforce the Sarcophagus.
This work was carried out by the State Research Institute of Building Constructions (NIISK), Kiev.
For a total number of 956 rooms technical information is now available in the data base. Accordingly the reactor building, the deaerator building, the auxiliary building and the machinery hall are described.
1.2 Systems and Equipment
This task contains the description of all systems and equipment installed in the Shelter before and after the accident, i.e. electricity supply systems, water supply and drains, ventilation system, measuring and monitoring systems, etc. This work was carried out by the NIISK in co-operation with the Chernobyl Nuclear Power Plant, Object Shelter (CNPPOS), Chernobyl.
Data base now contains the information on more than 1600 units of systems and equipment.
1.3 Radiological Situation
The scope of this work was the description of the radiological situation inside the Shelter, i.e. the dose rates of the radiation fields and the radioactive contamination in the rooms of the Shelter. These data are of special interest in order to estimate the radiation exposure in advance when planning work to be carried out by the personnel.
This work was carried out by the Russian Research Center “Kurchatov Institute” (RRCKI), Moscow, in co-operation with the CNPPOS.
Today the data base contains information of almost 1000 rooms.
1.4 Fuel Containing Materials and Radioactive Waste
The contents of this work was the description of the remaining fuel inside the Shelter, i.e. fragments of spent fuel elements, molten fuel lava, radioactive dust and Uranium and Plutonium solutes in the water in the lower rooms, the nuclide compositions, the physical and chemical properties etc.
These data are very important because of their direct meaning for risk estimates and measure for waste management. On the basis of these data for example, GRS together with RRCKI investigated the potential radiological consequences of a hypothetical roof collapse of the Sarcophagus followed by a release of radioactive dust as well as the criticality behavior of the fuel lava under the destroyed reactor vessel.
This work was carried out by the RRCKI in collaboration with the Institute of safety of atomic energy (IBRAE), Moscow, the Radium Institute Chlopin, (RICSP), St. Petersburg, and the Interdisciplinary Scientific and Technical Centre "Shelter" (ISTC), Chernobyl.
The data base contains now the information of about 97 assemblies of fuel containing materials. Among them are:
1.5 Environmental Impact
This work deals with the description of the influence of the accident to the Shelter site, i.e. the radiation situation above the ground, the contamination of the ground and the groundwater, the airborne effluents from the Sarcophagus and the radioactive air contamination at the Shelter site.
These data are also of special interest e.g. for planning preparation work near the Shelter for stabilization measures etc. This work was carried out by the ISTC.
1.6 Data Base Configuration and Data Integration
The scope of this work was the development of the data base structure, including the bibliography and the contributions of the different technical tasks, described above, as well as the development of a proper technique to retrieve the required information by key words as well as by the help of the optical navigation system ARCGIS. The data are organized and structured according to the main topics of contents described above in a data base under Microsoft Access.
The technical topics are subdivided into objects, e.g. rooms, construction elements, systems, equipment elements, measuring devices, fuel assemblies and fuel debris, pieces of fuel lave, etc., which are generally connected with the corresponding 3D co-ordinates (axis, row and height level). The 3D co-ordinates of the Shelter are prolonged also towards the industrial site allowing the description of the environmental impact to the Shelter site in a uniform co-ordinate system. The states of the objects are described by a text abstract and by the technical parameters with regard to the terms of references of the contracts. Auxiliary data, e.g. graphs, construction drawings, photos, original and animation videos, are also linked with the technical data to facilitate a better understanding.
The main technical quantities contained in the data base are always linked with the corresponding main sources of information described in the bibliography. A hint to the responsible contractor validating the technical data is also always given. All data are presented bilingual in English and in Russian using a switch button. All information available in the database can generally be retrieved by an optical navigation system based on ARCGIS. For each height level of the Shelter a 2D cross section containing the main objects, e.g. walls, doors, rooms, stairs, main constructions elements, newly filled concrete, fuel containing materials, main systems and equipment, etc. was elaborated.
Analogously, for the Shelter site a 2D cross sections containing data about the elevation levels of the territory, the radiation fields at height levels from 1 m up to 70 m above ground as well as about the groundwater table and the radioactive contamination of the groundwater was designed. From the ARCGIS platform a direct entry to the data base is released and all primary technical and auxiliary data can be found. Additionally, information from original and animation video films can be started.
Selected images can be viewed by means of the 3D analyst. This is of special interest for the whole Shelter and the industrial site as well as for different objects belonging to more than one height level. For such kind of objects also a direct access from the 3D images to the data base was realized.
This work was carried out by JV “ECOMM” Co., official distributor of ESRI, Kiev, Ukraine.
CONCLUSIONS AND LESSON LEARNED
The Sarcophagus project of the French-German Initiative for Chernobyl resulted in a consistent and comprehensive data base with approved data on building constructions, systems and equipment, nuclear fuel and radiological situation as well as environmental impact of the Chernobyl Sarcophagus.
The data base is presently in operation at GRS, IRSN, and the Chornobyl Centre. The data base was also given to the State Specialized Enterprise Chernobyl Nuclear Power Plant, Object Shelter, for expertise and review with the aim of application within the Shelter Implementation Plan (SIP). To facilitate this application a training workshop for SIP experts was organized. Another potential filed of application will be the licensing procedure at the State Nuclear Regulatory Commission of Ukraine.
During the project work consisting of collection, revision and approval of existing data also the creation of new data not available before took place. Also the comparison and unification of data among different contractors as well as the agreement on terms and key words, the creation of a common glossary and a common approach to the quality assurance procedures was a valuable result.
Supporting with this project the scientific-technical know-how at original institutions and keeping man power and qualification in place new working features and qualifications in common “western-eastern” working groups were developed.
The project stimulated also new interrelation between Ukraine, Russia and Belarus, the exchange of information and especially re-animated the Sarcophagus interest in Russia.
A new level of scientific-technical co-operation between Germany and France with Institutions of Ukraine, Russia and Belarus including the transfer of western know-how and methodology was practiced. Also a transfer of technical equipment and other resources. E.g. communication lines, computers, hard- and soft ware towards Ukraine took place.
4GRS Gesellschaft für Anlagen-und Reaktorsicherheit , Germany
5IRSN Institut de Radioprotection et de Sûreté Nucléaire, France
6CC Chernobyl Centre, Ukraine
G. Deville-Cavelin5 (IRSN), H. Biesold4 (GRS)
HISTORY, GOALS AND STRUCTURE OF THE PROJECT
Within the framework of the French-German Initiative for Chernobyl, Project n° 2 “Radioecology” was developed in order to describe the state of the environment after the accident.
The main goals of this project were :
Three groups of topics of common interest were defined by IRSN and GRS together with the experts of Ukraine, Belarus and Russia:
§ Transfers: in terrestrial environment, from terrestrial to aquatic environments, in the aquatic and in urban environments
§ Waste: inventory and characterisation of waste dumps, characterisation of waste (nature & quantity), impact assessment and management strategies
§ Countermeasures: in urban environment and in agricultural, semi-natural and natural environments.
After the signature of the general agreement in July 1997, Project n°2 was effectively launched in December 1998 by signing nine Specific Agreements for the corresponding sub-projects (SP) in the fields defined below:
SP 0: Ecological Portrait,
SP 1: Contamination of the Environment,
SP 2: Waste Dumps and Waste Strategies Management,
SP 3a: Soil-Plant Transfers,
SP 3b: Plant-Animal Transfers,
SP 3c: Runoff in an Agricultural or Natural Environment,
SP 3d: Transfer in Aquatic Environment,
SP 4: Urban Environment and Countermeasures,
SP 5: Countermeasures on Natural and Agricultural Areas.
In the course of the project, it appeared useful, even essential, to organise the data in a global database including all results of the project. Consequently, a last sub-project was agreed -SP6 - the "soft integrated" database named REDAC (Radioecological Database After Chernobyl).
Structure of the project
Besides the principles for choosing the different fields of work, the project management imposed in agreement with the experts of Ukraine, Belarus and Russia basic rules for fulfilling the sub-projects.
First, it was decided that each SP must include at least one team of each of the three countries involved, Belarus, Russia and Ukraine. A technical leader (Sub-project leader) represents the results of the three countries. Under his responsibility the regular reports are written and send to the project manager of IRSN and GRS.
Second, in order to optimise the work, the non-duplication of necessary data was aimed for. This led to make a preliminary stock-taking of the common data and the launch of the two "support" sub-projects "Ecological Portrait" (SP0) and "Initial contamination" (SP1)
1.2 General structure and participants
According to the principles and requirements mentioned, the global structure of the project "Radioecology" was the following (Figure 1)
For fulfilling these ten sub-projects in keeping with the programmes, principles and requirements, seven Belarussian, six Russian and eight Ukrainian institutes were involved, with the participation of sixty-seven researchers, scientists, engineers and technicians.
The main scientific and technical results of the different sub-projects are presented and explained in the different presentations and papers related to each SP. The database REDAC will also be presented with a demonstration at the end of the session.
Figure 1 : general structure of the "Radioecology" project
It is, however, to be noticed that there is a great amount of data of different sorts, constituting the available results of the project and the elements for future developments in environmental studies.
The main results of the radioecology project can be roughly summarised in the following way:
1.1 Transfer to plants and animals
The physical and chemical parameters of soils allow the study of their influence on migration in the soil-plant system and to animals and food. The large set of data collected over the years allows the definition of the main factors, especially time, affecting the transfer factors in the different parts of the food chain. The data, obtained under realistic conditions, can be used with high credibility in models for emergency situations.
1.2 Transfer by surface runoff and in the aquatic environment
The gathering of a large number of experimental results for the transfer of radionuclides by surface runoff in the Chernobyl zone and in the aquatic environment in the three affected countries made it possible to design, test, compare and validate models for the assessment of the contamination transfer. For radionuclide transfer to the biota, the kinetic parameters accumulation and elimination were found as the key values.
Since less than 50% of the disposal sites for waste of Chernobyl origin have been inspected so far, it is impossible to evaluate in full measure the real volumes and activity of the radioactive waste, its environmental impact and radiological hazard. The impact of the radioactive waste disposal sites on surface contamination is ascertained on the background of general surface contamination, much more for the flooded sites than for the others. The presence or absence of engineered barriers has a direct influence on the contamination level of the ground water. The most dangerous dumps, without barrier and partially flooded, contribute by about 60 % to the 90Sr contamination of the nearby phreatic tables.
1.4 Urban environment
In the urban environment, the efficiency of decontamination work is directly dependent on the level of contamination, the time elapsed after accident, and the organisation of the work. The tow efficiency of decontamination of various objects after the Chernobyl accident shows that the interaction of radioactive substances with surface and construction materials is of great importance.
1.5 Countermeasures in agricultural and natural environment
In the natural and agricultural environments, the efficiency of countermeasures, expressed by the reduction factor of radionuclide concentration in the final product, lies within a range of 3.0 to 9.0 in dependence of soil and crop properties. Soil cultivation was an effective countermeasure on radioactive land in the early period after fallout only. Surface and radical improvement of meadows are most practical countermeasures to use in contaminated meadow ecosystems, with an efficiency from 4 up to 20. The main influencing parameters are the soil and plant properties. Veterinary countermeasures and food processing of milk are also of striking efficiency. The very large amount of various data (description and efficiency) available for the different categories of countermeasures has to be noted.
1.6 Support Sub-projects- Early Contamination –Ecological Portrait
The administrative and environmental data are the most convenient basis for combining and organising the other scientific results of the project, but also those obtained in the "Health" Project n°3. The initial contamination was reconstructed and the results are close to the experimental evidence. Its distribution and changes were related to topographical and, for the most part, meteorological parameters.
1.7 Integration of results in REDAC
Through its structure and interactivity, made possible by the geocoding of spatial data, the soft integrated database REDAC, which is described and demonstrated elsewhere, provides a convenient way to manage and to use all the results coming from the project. All results for each topic are associated with their properties (databases, documents, reports) and are linked to related objects and to a common glossary for radioecology and environmental purposes. The "soft" integration is reached by computer organisational means and by using a cartographic system.
The performance of the project over about five years brought to the participants and to the management team a great amount of experience.
According to the extent of the damage and the repercussions for man and the environment, it was yet again confirmed that international collaboration is most efficient for dealing with the consequences of the Chernobyl accident. For the radioecological aspect, many data and results existed in the three affected countries, but due to the political evolution of the region, these were not easy to access. Moreover, the urgency of action during and just after the accident led to some misinterpretation and discrepancy of results which needed to be consolidated. This was one of the main goals of the "Radioecology" project and has been achieved.
It appeared necessary to build tools for managing potential similar post-accidental situations. A high-quality tool is easy and convenient to use and can also be extrapolated to analogous projects. This is why REDAC was constructed and developed. This data base answers well to the purpose it was built for, but is also suitable for other uses.
The first uses of the data gathered in REDAC shows clearly that the results of the project are well adapted to modelling in the different fields of environmental sciences. The assessment and explanatory models developed and tested on FGI P2 content show significant progress. This progress should be sustained and expanded.
From the human point of view, after some time and following the unavoidable problems when starting such a large collaboration, some renewed relationships emerged between the teams from the FSU. Furthermore, this work as a team during five years between the Franco-German management and the CIS organisations involved created some close ties beyond the strict scientific aspects. It was, so to speak, a mutual process of discovery touching all human and cultural facets, brought on by interesting and friendly exchanges. This human aspect of the project reinforced the efficiency of the collaboration of the different teams.
This "Radioecology" project should be considered as a necessary step towards widening knowledge in the wake of the Chernobyl accident. It results in a statement of what is known and consequently what should be to know in the future. According to the necessity and the trends in radioecology and environmental sciences, a certain outlook can be defined.
FUTURE OUTLOOK FOR ENVIRONMENTAL STUDIES
First, it is obvious that the environmental problems after the disaster as well as the health consequences will last for many decades, if not centuries. This is why studies have to continue. But in order to enhance their impact, the work to be undertaken must concern not only the Chernobyl area but also the general progress of environmental science and must not be limited to radioecology.
1.1 Direct outlook by deepening of knowledge
As a direct continuation of the work done in the "Radioecology" project, some topics should be more deeply investigated, i.e. reducing some uncertainties in contamination maps, defining a clear waste management strategy according to impact assessments to be performed, comparison, completion of data by similar ones existing elsewhere, extension to other radionuclides (transuranics) and other pathways, impact assessment through dose reconstruction, studying the efficiency of countermeasures in the urban environment more closely.
1.2 Further outlook
A more general further outlook should be considered for enhancing the appeal of the FGI-P2 results. The new projects have to take into account the recent progress in radioecology and the new directions of research in this field.
First, it is now necessary to study the environment not only as a pathway to the protection of humans but also as a target for protection against radiation. The impact on the environment itself and its different parts must be considered as a subject of research. The study on the effects of low doses on the environment, as it is now done for man, must also be included in these topics. Radionuclides should be considered as pollutants for the environment and their "radioecotoxicity" should be taken into account.
Otherwise, there is a great need for developing the means necessary for preparing post-accidental management of potential nuclear crises. The Chernobyl experience would be useful in providing decision-makers with technical, scientific and operational elements for fulfilling this task. In this context, developing global assessment models covering several ecosystems would be of a greatest interest and need.
Finally, the radiological situation in the Chernobyl area and its wide surroundings should be a good opportunity to focus on the radioecological sensitivity of ecosystems with a view to evaluating the acceptability of setting up nuclear facilities and to prepare post-accidental management.
M. Tirmarche5 (IRSN)
The risk of long term health effects after the Chernobyl accident was one of the major questions when starting our international collaboration. As this French-German Initiative (FGI) was launched more than 10 years after the accident, we had to focus preferentially on those health indicators that may be induced by radiation exposure and that are able to demonstrate an excess incidence after a relatively long latency period.
By supporting these studies, we expected to establish a common data base able to answer some of those questions concerning the exposed population, mainly by focusing on those having lived in relatively high contaminated areas.
Some more specific studies were also supported in order to bring a better information on a subgroup of the population: dosimetry of clean-up workers, psychologoical disorders in relation to the accident, specific risks for those having been exposed in utero, or at very young ages; description of the nutrition status in various areas.
Our objectives were different from those of some international analytical studies testing the dose-response relationship on some specific groups, with an individual reconstruction of dosimetry. Our concern was more to focus on descriptive studies comparing incidence rates for specific diseases between exposed and unexposed regions.
In each country a detailed description of the present status of the study is performed. Solid cancer studies and especially thyroid cancer incidence studies were all based on the same protocol :
1: description of quality and process of validation of the collected data;
2 : description of the number of cases per year, sex, and age group on national and regional (oblast) level;
3 : description of the population concerned : per age, sex and year.
In Belarus, the national cancer register was already installed before 1986 : it offered a unique opportunity to establish the baseline incidence rate of some rare diseases before the accident. In Ukraine retrospective validation of the data made it possible to have good quality of information for the post-Chernobyl period. The same validation was applied to the Russian data, stored at Obninsk, when considering the few oblasts having a relatively high post-Chernobyl contamination.
The trend of the annual incidence rates over the period 1986 to 1999 gives an indication of a possible increase, even if this increase is not necessarily linked to radiation of the Chernobyl accident. The advantage of these descriptive studies is a direct, in field description of a the health image of a specific, national or regional population, but an observed increase during a short or longer period may be due to several other factors that have to be tested and that may interact with the radiation effect.
Description of incidence trends of leukaemia for various age groups show no clear difference between exposed and unexposed regions, neither in Belarus. In Belarus, description of trends of leukaemia incidence over time for various age groups show no difference between exposed and unexposed regions.
In Ukraine, when comparing the results from male population living in Chernihiv and Sumy, a slight increase of the leukaemia risk for the “exposed” population cannot be excluded in the post-Chernobyl period. But, as this slight increase is not observed in the female population living in the same oblasts, it is difficult to conclude that environmental radiation exposure linked to the accident may be the only possible factor involved in this post-Chernobyl increase (other possible factors are evoked by the author of the study). In some oblasts in Russia, a slight, non statistically significant increase is observed when considering population exposed at very young ages. This last point demands a longer follow-up of this specific young exposed group.
For solid tumours, incidence rates in exposed and unexposed regions showed the same trends of increase over time; but, when considering more specifically some target organs, like thyroid, there was a clear increase in exposed regions.
For this specific disease, it is necessary to go in more details, considering influence of age at exposure and the possible co-factors. A high excess of thyroid cancer at very young ages was already reported when we started this initiative; consequently we decided to put our efforts on the collection and validation of those diagnoses observed on adolescents and adults. Presentation of the results of thyroid cancer trends have to be considered both in relation to age at diagnosis and to age at exposure in 1986. The latency period may be longer for exposure in adults than for exposure at very young ages. Women are known to have a higher risk for thyroid cancer than men: consequently we have to compare the relative risk for each sex separately, by comparing incidence rates of the same age groups. Regular screening through clinical and medical observations and with ultrasound devices may increase the detection of small nodules and small cancers, that would have been ignored over several years, if the screening techniques would not have been used in a systematic way.
In our data base, we have collected available information of the number of ultrasound devices installed per year in the studied oblasts.
Collection of the size of the tumours at diagnosis is a second information able to precise quality of screening over time.
Finally validation of the diagnosis through histology was the third step able to precise the increase of the different types of thyroid tumours. A blind international intercomparison test was realized in France, by realizing an expertise on the same histological slides by a panel of histopathologists from Belarus, Ukraine, France….
All this information is available through our HEDAC data base and several of our studies have been published in international journals.
After description of the data on national level, the second step was to focus on some specific oblasts in order to describe for populations with the same attained ages, the difference of the incidence rates in a low or high exposed population. As thyroid cancer is a relatively rare cancer disease, there is necessarily a large variation in the annual incidence rates, and the results may vary when comparing relatively small populations. Consequently long follow-up periods are necessary to have a global image of a population; on the other hand, some populations may have migrated from high to low exposed regions, and the thyroid cancers observed to-day in a low exposed region may be due to the fraction of the population having experienced a high exposure in 1986. Migration of the population is one of the factors that could disturb conclusions coming from descriptive geographical studies.
Most of these remarks are also applicable to the other studies having focused on solid cancers or on leukaemia incidences in high and low exposed oblasts. But thyroid cancers are strongly related to iodine intake; radioactive iodine levels per oblasts may be a strong predictor of a local thyroid cancer increase : we have tested this hypothesis and expect to go further in this direction; by collecting this information on a rayon level, as well as the incidence rates per age group and per year, we could combine the information from rayons having the same level of contamination, even if not necessarily from the same oblast. This work is presently going on. Collection of data describing any deficit of stable iodine on oblast level in the period preceding 1986 is also realized.
A second group of presentations focus on health problems in relation with exposures at very young ages : infant mortality and morbidity, in utero exposure and potential effects on brain, preconceptional and in utero exposure and congenital malformations. Those studies are not necessarily covering the three republics but give important indications when considering more specific problems in relation to radiation effects on foetus and very young babies. Systematic validation of basic data is a major advantage of these studies. Results of congenital malformations describe large results collected over Belarus, as this national register was existing since the 1980s and gives the possibility to compare trends before and after the accident. There was no evidence of a difference in the trends when comparing exposed and unexposed oblasts.
Nutrition status in Ukraine was studied with the idea to have a better information of some co-factors that could enter in the discussion of a global health image of an exposed population. Some biological parameters were also measured on specific subgroups.
By devoting a specific program to the topic of dosimetry of clean-up workers, we intend to give a global overview of the different groups of persons involved in various activities called liquidators or clean-up workers; it describes the difficulty of retrospective reconstruction of the exposure of these persons, and consider all available information able to describe the job exercised during the different tasks. Finally, it will show the possibility of individual retrospective reconstruction of the exposure to external radiation by the techniques (EPR) using dental enamel.
Presentation of the radiological passports is an important experience of regional risk management in Belarus, including collaboration with a large number of partners. A specific database is necessary for this approach.
This paper is not a detailed description of all the results that are included in our common French-German initiative but more a global description of the idea that was conducting this common program in close collaborations with the Ukrainian, Russian and Belarussian institutes. Validation of existing data, support for complementary information, and common protocol of analysis were the main lines of our collaboration. At present stage, not all the possible effects of the Chernobyl accident have been studied, mainly because some of them may rise after a long latency; but the basic data that are supporting our present descriptive analyses are in our common HEDAC database; final reports of the nineteen sub-projects are available and most of our results will be presented in our CD summarizing this conference. We hope that the initiated collaboration on international level will continue. Those who are interested in complementary research on these basic data have to take contact with the principal investigator of each topic and each country. Those who are expecting a synthesis on a specific topic can formulate their request to the database manager who will try to elaborate with the research team the appropriate answers.