L. I. Pavlovskyi1, V. M. Rudko1, D. V. Fedorchenko1,2, V. M. Antropov3,
O. G. Tretyak3
1Institute for Safety Problems of Nuclear Power Plants, NAS of Ukraine, 36a, Kirova st., Chornobyl, 07270, Ukraine
2National Science Center “Kharkiv Institute of Physics and Technology, NAS of Ukraine”, 1, Academichna st., Kharkiv, 61000, Ukraine
3State Specialized Enterprise “Centralized Enterprise for the Processing of Radioactive Waste”, 52, Kirova st., Chornobyl, 07270, Ukraine
Radioactive waste disposal site “Pidlisnyi” was commissioned in December, 1986. It is a surface storage facility with modular type design. Modules are formed by walls built from concrete blocks placed on common background of 1.5 m thick concrete slab. The storage facility was intended for disposal of radioactive waste with exposure rate from 5 R/h to 250 R/h. The A1 module survey of 2018 included studies of surface dose rates and also gamma ray well logging. During the survey, 16 wells were drilled down to the radioactive waste layer. Analysis of the drilling results revealed that thickness of radioactive waste layer varies from 0.7 to 2 m across the A1 module. Activity distribution in the radioactive waste layer is essentially nonuniform. According to the well logging data dose rate inside the well is within 7.5 to 130 mSv/h range. For the calculations, we developed spatial model of the storage facility based on the survey data. The model describes profiles of radioactive waste layer, concrete layer and gravel-sand covering. To build the model we divided module area into 16 rectangular fragments. For each fragment thicknesses of the corresponding layers were constant and defined by the drilling results. To assess the fuel amount and total radioactive waste activity for the A1 module of “Pidlisnyi” disposal site we used Monte Carlo simulation with MCNP5 transport code. The calculated value of the total activity of about 1.1 • 1015 Bq is close to the value obtained in the previous paper using simplified model and MicroShield code. We also performed assessment of the fuel amount inside the module using various approaches and found it to be below 0.8 % from total fuel amount in the Chor-nobyl NPP unit 4 before the accident.
Keywords: radioactive waste disposal site “Pidlisnyi”, radioactive waste, Monte Carlo method.
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