Radiological Conditions of the Western Kara Sea
Assessment of the radiological impact of the dumping of radioactive waste in the Arctic Seas
Background and project set-up - Rumours surfaced in 1992 that the former Soviet Union had, for over three decades, dumped radioactive wastes in the shallow waters of the Arctic Seas. The news caused great concern in many countries, especially those having an Arctic coastline.
In early 1993 the Office of President of Russia published a document with detailed information on the past dumping operations of the former Soviet Union. According to that document, the items dumped in the Arctic Seas included six nuclear submarine reactors containing spent fuel; a shielding assembly from an icebreaker reactor containing spent fuel; ten nuclear reactors without fuel; and solid and liquid low-level waste.
The solid high- and low-level wastes were dumped in the Kara Sea, mainly in the shallow fjords of Novaya Zemlya, where the depths of the dumping sites range from 12 to 135 meters and in the Novaya Zemlya Trough at depths of up to 380 meters. Liquid low-level wastes were released in the open Barents and Kara Seas.
In 1993, the IAEA responded to the concern of its Member States and the request of the Contracting Parties to the Convention on Prevention of Marine Pollution by Dumping of Wastes and Other Matter by launching the International Arctic Seas Assessment Project (IASAP). It had two objectives:
- To assess the risks to human health and to the environment associated with the radioactive wastes dumped in the Kara and Barents Seas
- To examine possible remedial actions related to the dumped wastes and to advise on their necessity and justification
The Project involved more than fifty experts from fourteen countries and was steered by an International Advisory Group. Its working areas consisted of:
- Examination of the radiological situation in Arctic waters
- Prediction of potential future releases from the dumped wastes
- Modelling of environmental transport of released nuclides and assessing the associated radiological impact on humans and biota
- Examination of the feasibility, costs and benefits of possible remedial measures
Current radiological situation
In the Project, information based on reactor operating histories and calculated neutron spectra were used to provide estimated radionuclide inventories of the dumped reactors and fuel assemblies. It was concluded that the total inventory of the high-level radioactive waste objects at the time of dumping was 37 PBq, and was estimated to be 4.9 PBq in 1994.
The open Kara Sea is relatively uncontaminated compared with some other marine areas. The main contributors to its artificial radionuclide content are direct atmospheric deposition and runoff of global fallout from nuclear weapon tests, discharges from reprocessing plants in western Europe and fallout from the Chernobyl accident.
Elevated concentrations of certain radionuclides were detected in sediments within a few meters of the low-level waste containers, suggesting that the containers have leaked. However, these leakages have not led to a measurable increase of radionuclides in the outer parts of the fjords or in the open Kara Sea.
Future radiological situation
The release rates of radionuclides to the environment depend upon the integrity of materials forming the reactor structure, the barriers added prior to dumping and the nuclear fuel itself. For each of the dumped high-level waste objects, the construction and composition of barriers were investigated in detail, and the best estimates of the corrosion rates and barrier lifetimes were used in the calculation of release rates. External events, such as collision with ships or, more generally, global cooling followed by glacial scouring of the fjords, could also damage the containment.
Three scenarios of radionuclide releases were considered:
- A best estimate scenario where release occurs via the gradual corrosion of the barriers, waste containers and the fuel itself
- Two catastrophic scenarios, causing at certain time points instant or accelerated release of the remaining radionuclide inventory
- The release rates were then used with mathematical models of the environmental behaviour of radionuclides to estimate radiation doses for selected population groups, for the world population, and for flora and fauna
For estimation of doses to individuals three population groups were considered: extreme seafood consumers, average North-east Russian population and a hypothetical group of military personnel patrolling the foreshore of the fjords. Calculations of individual doses were undertaken for time periods covering the peak individual dose rates for each of the three release scenarios.
According to all three scenarios the maximum annual individual doses for members of the public are small (less than 1 microSv) and very much less than variations in natural background doses. Doses to the hypothetical critical group of military personnel patrolling the fjords are higher but, nevertheless, comparable to natural background radiation doses (on average 2400 microSv)
Collective doses were estimated only for the best estimate release rate scenario. The total collective dose to the world’s population over the next 1000 years would be of the order of 10 man.Sv, about 90 % of which will be attributed to carbon-14.
The radiation dose rates to a range of populations of wild organisms, from zooplankton to whales, were found to be very low.
Project Conclusions
The Project reached a number of conclusions:
- Monitoring has shown that releases from identified dumped objects are small and localized to the immediate vicinity of the dumping sites
- Projected future doses to members of the public in typical local population groups arising from radioactive wastes dumped in the Kara Sea are very small, less than one microSv per year. Projected future doses to a hypothetical group of military personnel patrolling the foreshore of the fjords in which wastes have been dumped are higher, up to 4000 microSv per year but still of the same order as the average annual natural background dose
- Doses to marine fauna are insignificant, orders of magnitude below those at which detrimental effects on fauna populations might be expected to occur
- On radiological grounds remedial actions are not warranted.
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