SESSION 1
effect was the loss of a pine forest in the heavily exposed area; it will take decades for the forest to be re-established.
The acute radiobiological effects observed in the Chernobyl accident area are consistent with radiobiological data obtained in experimental studies or observed in natural conditions in other areas affected by ionizing radiation. Thus, rapidly developing cell systems, such as meristems of plants and insect larva, were predominantly affected by radiation. At the organism level, young plants and animals were found to be the most sensitive to acute effects of radiation.
Genetic effects of radiation, in both somatic and germ cells, were observed in plants and animals of the exclusion zone during the first few years after the Chernobyl accident. Both in the exclusion zone, and beyond, different cytogenetic anomalies attributable to radiation continue to be reported from experimental studies performed on plants and animals. Whether the observed cytogenetic anomalies have any detrimental biological significance is not known.
At the present time, the most remarkable effect on non-human biota is due to the absence of human pressure on the ecological system within the 30 km zone. Plant and animal species are flourishing.
7.ENVIRONMENTAL ASPECTS OF THE DISMANTLING OF THE CHERNOBYL SHELTER AND RADIOACTIVE WASTE MANAGEMENT
Construction of a shelter over the reactor between May and November 1986 was aimed at environmental containment of the damaged reactor, reduction of radiation levels on-site and the prevention of further release of radionuclides off-site. The shelter was erected in an extremely short period of time under conditions of severe radiation exposure to personnel. As a result, the measures taken to save time and cost during the construction led to imperfection in the newly constructed shelter as well as to a lack of comprehensive data on the stability of the damaged Unit 4 structures. The main potential hazard associated with the shelter is a possible collapse of its top structures and release of radioactive dust into the environment.
In order to avoid the effects of a potential collapse of the shelter in the future, measures are planned to strengthen unstable structures. In addition, an NSC with more than 100 years of service life is planned to be built as a cover over the existing shelter as a longer term solution. A rendition of the NSC is shown in Fig. 12. The construction of the NSC is expected to allow for the dismantlement of the current shelter, removal of highly radioactive fuel
69
ANSPAUGH
FIG. 12. Planned New Safe Confinement (NSC).
containing mass (FCM) from Unit 4, and the eventual decommissioning of the damaged reactor.
Both at the Chernobyl nuclear power plant site and its vicinity, large volumes of radioactive waste were generated, as a result of the cleanup of contaminated areas, and placed in temporary near surface waste storage and disposal facilities. These facilities were established without proper design documentation, engineered barriers or hydrogeological investigations and do not meet current waste safety requirements.
More radioactive waste is expected in the years to come. Waste will be generated during the construction of the NSC, possible dismantling of the original shelter, removal of FCM and decommissioning of Unit 4. This waste will consist of different categories, and waste of each category must be properly managed.
According to the Ukrainian National Programme on radioactive waste management, the long lived waste is planned to be placed in interim storage. Different storage options are being considered, and a decision has not yet been made. After construction of the NSC and decommissioning of the shelter facilities, it is envisaged that shelter dismantling and further removal of FCM will occur. High level radioactive waste is planned to be partially processed in
70
SESSION 1
place and then stored at a temporary storage site until a deep geologic disposal site is ready.
The future development of the exclusion zone as an industrial site or natural reserve depends on the future strategy for conversion of Unit 4 into an ecologically safe system, i.e. the development of the NSC, the dismantlement of the current shelter, the removal of FCM and the eventual decommissioning of the Unit 4 reactor site.
8.GENERIC RECOMMENDATIONS FOR FUTURE RESEARCH, REMEDIATION AND MONITORING
8.1. Radioactive contamination of the environment
Various ecosystems considered in the present report have been intensively monitored and studied during the years after the Chernobyl accident; the transfer and bioaccumulation of the more important long term contaminants, 137Cs and 90Sr, are now generally well understood. There is, therefore, little urgent need for major new research programmes on radionuclides in ecosystems; there is, however, a requirement for continued, but more limited, targeted monitoring of the environments, and for further research in some specific areas, as detailed below.
As activity concentrations in environmental compartments are now in quasi equilibrium and changing slowly, the number and frequency of sampling and measurements performed in monitoring and research programmes can be substantially reduced compared with the early years after the Chernobyl accident.
The deposits of 137Cs and a number of other long lived radionuclides in the 30 km zone should be used for radioecological studies of various ecosystems located in this highly contaminated area. Such studies are, except for very small scale experiments, not possible or difficult to perform elsewhere.
8.2. Countermeasures
Long term remediation measures and countermeasures should be applied in the areas contaminated with radionuclides, if they are radiologically justified and optimized.
Members of the general public should be informed, along with the authorities, about the existing radiation risk factors and the technological possibilities to reduce them in the long term by remediation and countermeasures. Members of the public should be involved in discussion and decision making.
71
ANSPAUGH
In the long term, after the Chernobyl accident, remediation measures and countermeasures remain efficient and justified — mainly in the agricultural areas with poor (sandy and peaty) soils, where high radionuclide transfer from soil to plants can occur. Particular attention must be given to the subsistence farming of several hundred settlements and about 50 intensive farms in Belarus, the Russian Federation and Ukraine, where radionuclide concentrations in milk still exceed national action levels.
Among long term remediation measures, radical improvement of pastures and grasslands, as well as the draining of wet peaty areas, is highly efficient. The more efficient agricultural countermeasures are pre-slaughter clean feeding of animals accompanied by in vivo monitoring; application of Prussian Blue to cattle; and enhanced application of mineral fertilizers.
Restricting harvesting by the public of wild food products, such as game, berries, mushrooms and fish from closed lakes may still be needed in areas where radionuclide activity concentrations exceed national action levels.
Advice should continue to be given on individual diets as a way of reducing consumption of highly contaminated wild food products, and on simple cooking procedures to remove radioactive caesium.
The unique experience of countermeasure application after the Chernobyl accident should be carefully documented and used for the preparation of international and national guidance for authorities and experts responsible for radiation protection of the public and the environment.
Recommendations for decontamination of the urban environment in the event of large scale radioactive contamination should be distributed to the management of nuclear facilities having the potential for substantial accidental radioactive release (nuclear power plants and reprocessing plants) and to authorities in adjacent regions.
An important issue that requires more sociological research is the perception by the public of the introduction, performance and withdrawal of countermeasures in the event of emergencies, as well as the development of social measures aimed at involving the public in these processes at all stages, beginning with the decision making process.
There still is substantial diversity in the international and national radiological criteria and safety standards applicable to the remediation of areas affected by environmental contamination with radionuclides. The Chernobyl experience has clearly shown the need for further international harmonization of appropriate radiological criteria and safety standards.
72
SESSION 1
8.3. Human exposure
Large scale monitoring of foodstuffs, whole body counting of individuals and provision of thermoluminescent detectors to members of the general population are no longer necessary. The critical groups in areas of high contamination and/or high transfer of radiocaesium to foods are known. Representative members of these critical groups should be monitored by dosimeters for external dose and by whole body counting for internal dose.
Sentinel or marker individuals in more highly contaminated areas not scheduled for further remediation might be identified for continued periodic whole body counting and monitoring for external dose. The goal would be to follow the expected continued decrease in external and internal dose rate, and to determine whether such decreases are due to radioactive decay alone or to further ecological elimination.
8.4. Radiation-induced effects on plants and animals
In order to develop a system of environmental protection against radiation, the long term impact of radiation on plant and animal populations should be further investigated in the exclusion zone of the Chernobyl accident; this is a unique area for radioecological and radiobiological research in an otherwise natural setting.
In particular, multigenerational studies of radiation effects on the genetic structure of plant and animal populations might bring fundamentally new scientific information.
There is a need to develop standardized methods for the reconstruction of dose to non-human biota, e.g. in the form of a unified dosimetric protocol.
Protective actions for farm animals in the event of a radiological emergency should be developed and internationally harmonized based on modern radiobiological data, including the experience gained in the Chernobyl exclusion zone.
It is likely that any technologically based remediation actions aimed at improving the radiological conditions for plants and animals in the exclusion zone of the Chernobyl nuclear power plant would have adverse impacts to biota.
8.5.Environmental aspects of dismantling the Chernobyl shelter and radioactive waste management
Because safety and environmental assessments have only been performed for individual facilities at and around the Chernobyl nuclear power
73