Territory contamination with the radionuclides representing the fuel component of Chernobyl fallout

Title: Territory contamination with the radionuclides representing the fuel component of Chernobyl fallout

Author: V.A Kashparov, S.M Lundin, S.I Zvarych, V.I Yoshchenko, S.E Levchuk, Y.V Khomutinin, I.M Maloshtan, V.P Protsak

Reference: Science of The Total Environment, Volume 317, Issues 1–3, 30 December 2003, Pages 105-119

DOI: http://dx.doi.org/10.1016/S0048-9697(03)00336-X

Keywords: Chernobyl accident; Terrestrial density of contamination; Plutonium; Radioactive fallout; Fuel particles

Abstract: The data obtained through a series of experiments were used to specify the correlation of activities of the fuel component radionuclides of Chernobyl fallout and to create the maps of the 30-km Chernobyl zone terrestrial density of contamination with ¹⁵⁴Eu, ²³⁸Pu, ^239+240Pu and ²⁴¹Am (on 01.01.2000). In the year 2000, total inventories of the fuel component radionuclides in the upper 30-cm soil layer of the 30-km Chernobyl zone in Ukraine (outside the ChNPP industrial site, excluding the activity located in the radioactive waste storages and in the cooling pond) were estimated as: ⁹⁰Sr—7.7×10¹⁴ Bq; ¹³⁷Cs—2.8×10¹⁵ Bq; ¹⁵⁴Eu—1.4×10¹³ Bq; ²³⁸Pu—7.2×10¹² Bq; ^239+240Pu—1.5×10¹³ Bq; ²⁴¹Am—1.8×10¹³ Bq. These values correspond to 0.4–0.5% of their amounts in the ChNPP unit 4 at the moment of the accident. The current estimate is 3 times lower than the previous widely-cited estimates. Inventories of the fuel component radionuclides were also estimated in other objects within the 30-km zone and outside it. This allowed more accurate data to be obtained on the magnitude of a relative release of radionuclides in the fuel particles (FP) matrix during the Chernobyl accident outside the ChNPP industrial site. It amounts to 1.5±0.5% of these radionuclides in the reactor, which is 2 times lower than the previous estimates. Two-thirds of the radionuclides release in the FP was deposited on the territory of Ukraine.

URL: http://www.sciencedirect.com/science/article/pii/S004896970300336X

Fuel particles in the Chernobyl cooling pond: current state and prediction for remediation options

Title: Fuel particles in the Chernobyl cooling pond: current state and prediction for remediation options

Author: A. Bulgakov, A. Konoplev, J. Smith, G. Laptev, O. Voitsekhovich

Reference: Journal of Environmental Radioactivity, Volume 100, Issue 4, April 2009, Pages 329-332

DOI: http://dx.doi.org/10.1016/j.jenvrad.2008.12.012

Keywords: Chernobyl; Cooling pond; Fuel particles; ⁹⁰Sr; Dissolution; Remediation

Abstract: During the coming years, a management and remediation strategy for the Chernobyl cooling pond (CP) will be implemented. Remediation options include a controlled reduction in surface water level of the cooling pond and stabilisation of exposed sediments. In terrestrial soils, fuel particles deposited during the Chernobyl accident have now almost completely disintegrated. However, in the CP sediments the majority of ⁹⁰Sr activity is still in the form of fuel particles. Due to the low dissolved oxygen concentration and high pH, dissolution of fuel particles in the CP sediments is significantly slower than in soils. After the planned cessation of water pumping from the Pripyat River to the Pond, significant areas of sediments will be drained and exposed to the air. This will significantly enhance the dissolution rate and, correspondingly, the mobility and bioavailability of radionuclides will increase with time. The rate of acidification of exposed bottom sediments was predicted on the basis of acidification of similar soils after liming. Using empirical equations relating the fuel particle dissolution rate to soil and sediment pH allowed prediction of fuel particle dissolution and ⁹⁰Sr mobilisation for different remediation scenarios. It is shown that in exposed sediments, fuel particles will be almost completely dissolved in 15–25 years, while in parts of the cooling pond which remain flooded, fuel particle dissolution will take about a century.

URL: http://www.sciencedirect.com/science/article/pii/S0265931X08002324

90Sr migration to the geo-sphere from a waste burial in the Chernobyl exclusion zone

Title: 90Sr migration to the geo-sphere from a waste burial in the Chernobyl exclusion zone

Author: L Dewiere, D Bugai, C Grenier, V Kashparov, N Ahamdach

Reference: Journal of Environmental Radioactivity, Volume 74, Issues 1–3, 2004, Pages 139-150

DOI: http://dx.doi.org/10.1016/j.jenvrad.2004.01.019

Keywords: Chernobyl; Strontium-90; Fuel particles; Groundwater; Retardation; Sorption; Hydro-dispersion

Abstract: Results are presented from an ongoing field-scale experimental study (namely the Chernobyl Pilot Site project) aimed at characterization of processes controlling ⁹⁰Sr releases from a shallow trench containing nuclear fuel particles, and subsequent radionuclide transport in the underlying sandy aquifer at the Chernobyl nuclear power plant site. Microscopic analyses of waste material and leaching experiments have shown that 10–30% of the radioactive inventory is associated with chemically extra-stable Zr–U–O particles. The largest fraction of ⁹⁰Sr activity in the trench (≈30–60%) is currently associated with relatively slowly dissolving non-oxidized UO₂ matrix fuel particles. The ⁹⁰Sr migration velocity in the eolian sand aquifer is retarded by sorption to ≈9% of groundwater flow velocity (K_d ≈ 2 ml/g). The dispersivity values for non-reactive solute transport in the aquifer predicted by geostatistics (i.e. 0.8 6 cm) were confirmed by a natural gradient tracer test using ³⁶Cl. The observed negative correlation between hydraulic conductivity and K_d of aquifer sediments suggests that ⁹⁰Sr could be subjected to larger dispersion in the subsurface compared with ³⁶Cl.

URL: http://www.sciencedirect.com/science/article/pii/S0265931X04000244

Kinetics of dissolution of Chernobyl fuel particles in soil in natural conditions

Keywords: Chernobyl; Fuel particles; Dissolution kinetics; Sr-90; Mobility; Soil

Abstract: Kinetic of fuel particles dissolution under natural environmental conditions has been investigated using the data on ⁹⁰Sr speciation in soils collected from 1995 to 1997 within the Chernobyl nuclear power plant 50 km zone. The dependency of fuel particles dissolution constants on the soil acidity (pH=4–7) has been obtained on the basis of large and statistically reliable experimental data. Results show that between 2 and 21% of ⁹⁰Sr activity is associated with weathering resistant fuel particles. Therefore, these particles would not influence the radiological situation in the near future. The map of the main agrochemical characteristics and the map of the fuel particles dissolution constants have been created for the 30-km zone territory. According to the prognosis of dynamics of fuel particles dissolution in the investigated zone, a radiological situation along the fuel paths of radioactive fallout in present time reached a stable state. An increasing in absolute contents of ⁹⁰Sr mobile forms in neutral soils will be observed in the next 10–20 yr. However, the difference between the maximum level of mobile forms contents and their existing contents will not exceed 20%.