Conjugated heat transfer analysis of the Start-Up Monitoring Module (STUMM) for IFMIF-DONES including heat generation mapping

Abstract

The Start-Up Monitoring Module (STUMM) is designed for the commissioning phase of the IFMIF-DONES (International Fusion Materials Irradiation Facility – Demo Oriented NEutron Source). The main aim is the detailed characterization of the irradiation field in space for the validation of the nuclear models. The thermo-hydraulic analysis of the STUMM was carried-out in the Ansys FLUENT software predicting the steady-state temperature distribution in the full range of the allowable inlet temperatures (15–60 °C), inlet pressures (3–3.5 bar), and the maximum allowable helium flow rate of 0.18 kg/s. The heat generation maps obtained from MCNP analyses were mapped on the CFD mesh via the in-build FLUENT functionality of “profiles”. To ensure the conservation of the global heat generation a correction coefficient αcorr was introduced to modify the MCNP profiles before the import to CFD: qCFD(x,y,z)=αcorr qMCNP(x,y,z). A dedicated test case of a cylinder subjected to a point irradiation source was studied, confirming the convergence of the global heat with a refinement of the MCNP and CFD discretization, where the MCNP model was discretized with cuboid cells and the CFD with a polyhedral. The global STUMM model was solved with 5 MCNP profiles with cell sizes from 5 mm to 1 mm (0.2–23.3 mln data points). Even though the smallest feature of the global CFD model was 0.5 mm (thickness of a detector wall) the MCNP profile with ∼4 mm cuboid cells gave almost identical results to the finest 1 mm profile, confirming the precision of the method and no need of solving very finely discretized MCNP models. With the direct transfer of results between MCNP and CFD model with the in-build FLUENT functionality of “profiles”, the simulation set-up was fast. A negligible impact of the internal radiation heat transfer on the temperatures was found (with the Discrete Ordinates (DO) model). Two possible flow directions of the helium were analysed for the worst-case scenarios. With the maximum pressure drop of 4.12 kPa, the maximum helium outlet temperature of 71.6 °C, and the max temperature of the detectors of 157.5 °C all the design requirements were satisfied, as values were far from the limits of 60–80 kPa, 150 °C and 250 °C respectively.