Toward the design validation of water-cooled ceramic Breeder Test Blanket Module in physical mock-up testing

Abstract A large-scale heat flux testing methodology for the water‑cooled ceramic breeder (WCCB) Test Blanket Module (TBM) submodule, the leading blanket concept for Japan’s DEMO reactor, was developed and demonstrated using a newly constructed electron‑beam (EB) heat load facility. To reproduce ITER‑relevant thermal conditions, dedicated calibration techniques were established to determine the net heat flux intensity, EB beam profile, and non‑destructive surface temperature measurement capability. A calorimeter composed of seven F82H heat‑receiving elements was designed to quantify the net heat flux reaching the mock‑up surface. Using this method, the nominal ITER TBM heat flux of 0.30 MW/m² was successfully achieved with a spatial variation within ±0.02 MW/m², establishing optimal EB parameters of Ic = 550 mA and Ub = 30 kV. The EB beam profile, evaluated using a newly developed Faraday cup with adjustable shielding, exhibited a Gaussian distribution with a diameter of 27.6 mm. A non‑contact infrared (IR) temperature measurement technique was developed using a dedicated calibration specimen, achieving agreement with thermocouple measurements within 6.6% up to 550°C. Based on these calibrations, a full‑scale physical mock‑up of the WCCB TBM submodule was irradiated at 0.30 MW/m² for 60 s under PWR‑like coolant conditions (280°C, 15.5 MPa). The measured temperature evolution showed good agreement with transient thermal analysis in the initial heating phase, while steady‑state deviations were attributed to EB‑induced surface emissivity changes and oxidation. Post‑test examinations based on ITER divertor acceptance criteria revealed no melting, coolant leakage, weld detachment, or thermal hot spots. These results demonstrate the validity of both the WCCB TBM design and the developed heat flux testing techniques, establishing a robust foundation for upcoming qualification tests toward ITER installation.