The water-cooled ceramic breeder blanket (WCCB) is one of the blanket candidates for the Chinese fusion engineering test reactor (CFETR). The conceptual of WCCB for CFETR under 200-MW fusion power has been designed based on pressurized water-cooled reactor technology. RELAP5 code, which is mature and often used in transient thermal-hydraulic analysis in pressurized water reactor, was selected as the simulation tool. In this paper, the nodal model for RELAP5 was developed corresponding to typical WCCB module, i.e., the coolant passages inside the module were nodalized as hydrodynamic components, and the associated module components were simulated with 1-D heat structures. The steady-state characteristic under full power was analyzed. The stable fluid, wall temperature distributions, and pressure drops were studied. The results were compared with those of the 2-D and 3-D computational fluid dynamics analyses by FLUENT. Furthermore, the transient characteristics under three accidental scenarios, in-vessel loss of coolant accident (LOCA), in-box LOCA, and ex-vessel LOCA, were analyzed, respectively. Simulation results show that the cooling of stiffening plates and side walls for breeder zone is very important for the blanket module. All the pressurization of the related volumes is within the design limits. The temperature of the structures does not exceed the limits for a relatively long time that allows mitigation measures to be taken. As for in-box LOCA, the exclusion of Be-water reaction makes the temperature nonconservative and still needs further study.

The departure from nuclear boiling (DNB) is an essential point for the heating channel with water flowing through, because when it happens, the water near the heated wall can be dried out, which will cause the material temperature exceeding the upper limits. Presently, the blanket is under design phase, and some essential parameters are uncertain, including the heat flux on the first wall (FW). For the sake of thermal safety, the occurrence conditions of DNB are analyzed solely, regardless whether material temperature exceeds the limits or not, in the FW of water-cooled ceramic breeder blanket for Chinese Fusion Engineering Reactor. This paper is useful for further blanket thermal design. Based on the lookup table that is summarized by experiments for the uniformed heating circular tube of 8 mm diameter, the local critical volumetric fraction of vapor, which acts as the evaluation criteria for the U-shaped FW of square channel with one-sided heating, is obtained using a computational fluid dynamics approach under different DNB operating conditions. After the comparison of phase distribution between different turbulence models, the K-$\Omega $ model is selected to do the calculation. The effects of coolant inlet temperature, mass flow rate, and operating pressure on DNB value are evaluated. Under the same operating pressure, either increasing mass flux or decreasing inlet temperature can reduce the critical vapor fraction. On the contrary, the DNB is enlarged effectively. Under the same inlet conditions, the lower operating pressure can increase DNB because of the higher latent heat of vaporization.

A new type of Water Lead Lithium Cooled (WLLC) blanket that adopts the modular design scheme, water cooling the structure components, liquid PbLi as breeder and coolant, and SiC as the thermal insulator between PbLi and structures is under development as a candidate blanket concept for the Chinese Fusion Engineering Test Reactor (CFETR). Based on a poloidal-radial slice model, thermal hydraulic analysis is performed for this blanket to validate the feasibility of design goals. Results show that the present design can achieve the outlet temperature in the range of 600–700 °C, with all the material temperatures safely below the upper limits. A series of sensitivity analyses are also carried out. It indicates that the thermal conductivity (TC) of SiC would have a significant influence on the temperature field, streamlines and pressure drop; that is, lower TC of SiC can maintain the temperature of PbLi at a high level, and induce an increased number of vortices in the liquid PbLi flow as well as a larger pressure drop. On this basis, the joint effects of the TC of SiC and inlet velocity on the performance of blanket thermal hydraulics are analyzed, then the so-called “attainable region” is proposed. Finally, optimization design studies are carried out by decreasing the width of the front channel. Comparison results show that the present design is the most reasonable.

The supercritical carbon dioxide (S-CO2) cOoled Lithium-Lead (COOL) blanket is under development for China Fusion Engineering Test Reactor (CFETR). As a key component of the blanket, the First Wall (FW) is subjected to high heat flux and plasma sputtering, requiring the simultaneous satisfaction of stringent thermal and structural requirements. To reduce the prohibitive computational cost of high-fidelity simulations when exploring vast design spaces, a thermo-mechanical coupled surrogate model is developed, which integrates the FW geometry, heat loads and boundary conditions as parametric inputs. By combining thermal balance theory, empirical correlations and 1D/2D hybrid analytical heat conduction model, the surrogate model enables the rapid prediction of key thermal-hydraulic responses, including coolant outlet temperature, pressure drop and temperature distribution of RAFM steel. Based on the temperature distribution, the corresponding stress quantities are evaluated using generalized Hooke’s law, beam theory and plate theory. To improve the consistency of thermo-mechanical stress prediction, FEM-derived stress linearization results are further used to correct the analytical stress quantities, leading to a corrected thermo-mechanical surrogate model. Through consistency assessment against CFD/FEM simulations and FEM-based correction, the corrected surrogate model shows improved agreement with numerical results while retaining sub-second computational performance, making it suitable for rapid pre-design screening within the investigated parameter range. On this basis, a multi-objective optimization framework employing the Non-dominated Sorting Genetic Algorithm II (NSGA-II) for FW design is established. Taking the equatorial unit #3 of COOL blanket as an example, the framework is applied to optimize the coolant channel geometry and mass flow rate, with the objectives of maximizing outlet temperature and minimizing the flow-resistance power loss associated with the FW pressure drop to improve the thermal-to-electric conversion efficiency under multi-physics constraints. The optimization result is a nonlinear Pareto-Front curve describing the trade-off between these competing objectives. Two representative solutions on the curve are selected for detailed comparison with the baseline design: one design maintains a similar outlet temperature while reducing flow-resistance power loss by 22.67%, whereas the other maintains comparable flow-resistance power loss but increases the outlet temperature by 8.31 ℃. Moreover, all solutions between these two points on the Pareto-Front outperform the baseline design in both objectives. Overall, the proposed surrogate-based optimization framework demonstrates its capability to efficiently identify high-performance designs via balancing competing objectives and provides a flexible and systematic tool for thermo-mechanical pre-design screening and optimization of the CFETR COOL blanket FW.