Yu. A. Olkhovik
SI “The Institute of Environmental Geochemistry of the National Academy of Sciences of Ukraine”, 34a, Palladin ave., Kyiv, 03142, Ukraine
The problems of irradiated reactor graphite conditioning, which make up the active zone of RBMK reactors of Chornobyl NPP Units 1-3, which are decommissioned, are considered. The total volume of graphite blocks is 3 700 m3. The radiological danger of irradiated graphite is due to the presence of long-lived 14C and 36C1 radionuclides, defines the long-term radiological hazard of radioactive waste in the form of reactor graphite. So far, Ukraine has not defined a strategy for the treatment of irradiated reactor graphite. The purpose of this publication is to evaluate the impact of irradiated Chornobyl reactor graphite on the environment under possible scenarios for its disposal. The possible consequences of reactor graphite disposal in a hypothetical surface storage facility organized on the lower floor of a power unit building after the end of the equipment dismantling phase were considered in the event of a decision on site disposal. The carbon leaching rate of irradiated graphite from Magnox (UK), Hanford (USA) and G-2 (France) reactors has been generalized. The estimated leaching rate of 14C from irradiated graphite is 1.65E-6 g/ cm2 • day, which is close to the rate of leakage of radionuclides from the glass matrix. The calculations performed with the involvement of literature data on leaching of radionuclide 14C indicate the likelihood of unacceptable impact of radiocarbon on the environment in the event of the scenario of disposal of irradiated reactor graphite in the surface storage. It is concluded that reactor graphite disposal at the Chornobyl NPP should occur only in geological storage in deep horizons of slow water exchange. Possible technologies of creation of additional engineering protective barriers at disposal of irradiated reactor graphite are considered. A thin layer of the naturally stable material, for example Gold or Carborundum (SiC), applied to a graphite block could serve as an additional engineered barrier for thousands of years.
Keywords: irradiated reactor graphite, disposal, leaching, migration, radiocarbon.
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