Comparison of the radiological hazard of thorium and uranium spent fuels from VVER-1000 reactor

• Spent thorium and uranium fuel composition in VVER-1000 was calculated by MCNPX.
• Important nuclide 208Tl is not included in the thorium spent fuel composition.
• There are large differences in activity of actinides between spent Th and U fuels.
• Dose rate from spent thorium fuel is increasing during 50 years of decay.
• Tl208 in spent thorium fuel increased the dose rate by several percent.

Thorium fuel is considered as a viable alternative to the uranium fuel used in the current generation of nuclear power plants. Switch from uranium to thorium means a complete change of composition of the spent nuclear fuel produced as a result of the fuel depletion during operation of a reactor. If the Th–U fuel cycle is implemented, production of minor actinides in the spent fuel is negligible. This is favourable for the spent fuel disposal. On the other hand, thorium fuel utilisation is connected with production of 232U, which decays via several alpha decays into a strong gamma emitter 208Tl. Presence of this nuclide might complicate manipulations with the irradiated thorium fuel.Monte-Carlo computation code MCNPX can be used to simulate thorium fuel depletion in a VVER-1000 reactor. The calculated actinide composition will be analysed and dose rate from produced gamma radiation will be calculated. The results will be compared to the reference uranium fuel. Dependence of the dose rate on time of decay after the end of irradiation in the reactor will be analysed. This study will compare the radiological hazard of the spent thorium and uranium fuel handling.