Numerical Study on Multiscale Heat Conduction Problems in Very High Temperature Reactor Fuel Pebble Based on OpenFOAM

Pebble bed very high temperature reactor (VHTR) has been identified as one of six Generation-IV (Gen-IV) types of reactor which could operate at a high thermal power. The calculation of the temperature in the fuel pebble is a key part of VHTR thermal hydraulics numerical simulation. However, due to the special structure of the VHTR fuel pebble, the temperature calculation involves a multiscale problem. The multiscale heat conduction model includes mesoscale temperature of fuel pebble and microscale temperature of TRISO fuel particles calculation. To deal with the particularity of temperature calculation of the fuel pebble, this paper presents a multiscale heat conduction model based on an open source CFD package OpenFOAM. Firstly, the quasi steady state heat conduction method (QSSHC) and homogeneous layers method (HL) was verified by a simple multiscale model. The results show that the QSSHC method has a good ability of multiscale temperature prediction. Secondly, the mesoscale temperature distribution and the maximum temperature in the microscale of VHTR fuel pebbled are calculated with QSSHC method based on OpenFOAM. This multiscale solver will be couple with other solvers of OpenFOAM, to provide a new perspective of VHTR simulation.

Characterising U-232 and Tl-208 Buildup and Decay on Thorium-fuelled RGTT200K

Thallium-208 (Tl-208), a decay daughter of uranium-232 (U-232), is a strong 2.6 MeV gamma emitter present in significant amount in thorium fuel cycle. Its existence enhances the anti-proliferation characteristics of thorium fuel cycle, but at the same time complicates the fuel handling system. In order to ensure that radiation hazard is properly contained, the buildup and decay characteristics of both U-232 and Tl-208 need to be understood. This paper aimed to provide a characterisation on U-232 and Tl-208 buildup in the thorium-fuelled RGTT200K, a 200 MWt very high temperature reactor (VHTR) developed by BATAN, using ORIGEN2.1 depletion code. Pure and impure U-233 were used as the fissile nuclide for comparison. The result showed that U-232 buildup rate is faster in pure U-233, but its Tl-208 buildup is slower. Nonetheless, pure U-233 always has its U-232 and Tl-208 activity lower than impure U-233. Accordingly, both U-232 and Tl-208 radioactivity post-discharge in pure U-233 are lower than impure U-233, although the difference become somewhat negligible after 300 years of decay. Tl-208 activity peaked after 10 years of decay, necessitating different approach in managing post-discharge fuel management.

Isochronous Stress-Strain Curves for Alloy 617

Alloy 617 is a high temperature nickel based material that could have significant design advantages when compared to austenitic steels in very high temperature reactor applications. Several high temperature design methods, including Section III, Division 5 of the ASME Boiler & Pressure Vessel Code, require a model for the creep and high temperature plastic deformation of a material, quantified as a set of isochronous stress-strain curves. This paper describes the development of a model for the high temperature deformation of Alloy 617. This model is then used to generate design hot tensile and isochronous stress strain curves suitable for use in Section III, Division 5 and other high temperature design methods.

Experimental Investigation of 14C in the Primary Coolant of the 10 MW High Temperature Gas-Cooled Reactor

ABSTRACTThe very high temperature reactor (VHTR) is a development of the high-temperature gas-cooled reactors (HTGRs) and one of the six proposed Generation IV reactor concept candidates. The 10 MW high temperature gas-cooled reactor (HTR-10) is the first pebble-bed gas-cooled test reactor in China. A sampling system for the measurement of carbon-14 (14C) was established in the helium purification system of the HTR-10 primary loop, which could sample 14C from the coolant at three locations. The results showed that activity concentration of 14C in the HTR-10 primary coolant was 1.2(1) × 102 Bq/m3 (STP). The production mechanisms, distribution characteristics, reduction routes, and release types of 14C in HTR-10 were analyzed and discussed. A theoretical model was built to calculate the amount of 14C in the core of HTR-10 and its concentration in the primary coolant. The activation reaction of 13C has been identified to be the dominant 14C source in the core, whereas in the primary coolant, it is the activation of 14N. These results can supplement important information for the source term analysis of 14C in HTR-10 and promote the study of 14C in HTGRs.