Thermal Properties of Simulated High Burn up Nitride Fuels and Nitride ADS Targets
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1043-T13-03
Thermal Properties of Simulated High Burn up Nitride Fuels and Nitride ADS Targets Masayoshi Uno1, Ken Kurosaki1, Shinsuke Yamanaka1, and Kazuo Minato2 1 Division of Sustainable Energy and Environmental Engineering, Osaka University, Yamadaoka 2-1, Suita.Osaka, 565-0871, Japan 2 Japan Atomic Energy Agency, Tokai-Mura, Naka-gun, Ibaraki, 319-1195, Japan ABSTRACT We made various nitride fuels containing simulated FP elements and evaluated the effect of these FP elements on the properties of the nitrides. For Uranium Neodymium nitride solid solution the lattice parameter increased with Nd content, thermal expansion coefficient did not change and thermal conductivity decreased with Nd content. The thermal expansion for UN containing Pd, where Pd precipitated as UPd3 in the grain boundaries of UN, was nearly the same as that of UN and the thermal conductivity of UN containing Pd decreased with Pd content. For UN containing Mo Molybdenum precipitated as pure metal isotropically. Both the thermal expansion and thermal conductivity did not vary with Mo content. This might result from the low Mo contents at these simulated burnups. INTRODUCTION Nitride fuels are under consideration as the advanced fuel of FBR [1,2] and the targets of Accelerate Driven System (ADS) [3,4] because of their superior thermal, neutronic properties and so on. However, there is few data for the properties of nitride fuels at high burn-up. In the present study, we made various nitride fuels containing simulated FP elements and evaluate the effect of these additives on the properties of the nitrides. EXPERIMENTAL PROCEDURE Powder sample of UN or (U,Nd) solid solution was prepared by a carbothermic reduction of uranium dioxide (UO2) or the mixture of UO2 and Nd2O3 at 1773K under N2 or N2and 5%H2 gas. Pd or Mo as FP element was mixed with the nitride powder, pressed and heat treated at 2073K under Ar atmosphere. The amount of the FP element was determined so that the simulated burnup was to be 50 and 200 GWd/tU. The composition of the samples is shown in Table 1 where Nd, Pd or Mo simulates the FP elements, which form the solid solutions with UN, which form the intermetallic compounds with U or which precipitate as the pure metals, respectively. Table 1 The composition of the sample Added FP element Nd Chemical form
(U,Nd)N
Pd
Mo
UN+UPd3
UN+Mo
Simulated burnup(MWd/t)
50
200
50
200
50
200
Added amount (mol%)
2.7
12.2
2.2
11.2
1.6
7.1
The thermal expansion, heat capacity and thermal diffusivity of the samples were measured using the thermal dilatometer, DSC and laser-flash method, respectively. The thermal conductivity was calculated from thus obtained capacity, thermal diffusion data and the density. The estimated thermal conductivity was further normalized to that of the sample with 100% theoretical density using Maxwell-Eucken’s equation[5,6], κ (P ) = κ (0)
1− P 1 + βP
where κ is thermal conductivity, ρ is volume fraction of porosity and β is unity. RESULTS AND DISCUSSION (U,Nd)N X-ray diffraction analysis showed th
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