Analysis of Isotopic Contributions to Doppler Coefficients of Inert Matrix Fuels

The Minor Actinides (MA) generated by nowadays PWRs fleet has significant impact on environment and biosphere. Inert Matrix Fuels (IMF) is a possible way to reduce the production and hazard of MA in recent. From neutronic aspect, using the MCNP code with temperature related continuous neutron data, the present paper analyses the isotopic contributions to the Doppler Coefficients of certain types IMF fuels. It is concluded that, the Doppler Coefficients of Al₂O₃+ZrO₂+MgO and ZrO₂ based IMF fuels are much smaller than those containing ThO₂, since the low neutron absorptions and lacking of resonance broadening of Al, Zr, Mg and O elements. For the same Inert Matrix, Reactor Grade Plutonium (RG-Pu) IMF fuels have more negative Doppler Coefficients than Weapon Grade Plutonium (WG-Pu) IMF fuels, which induce by the more abundance of resonance isotopes ²⁴⁰Pu, ²⁴²Pu in RG-Pu. Since the different neutron absorption cross-section profiles, the Er₂O₃ burnable poison has negative contribution to the Doppler Coefficient, however ¹⁰B, a typical 1/v absorber, is on the contrary way.