The Water-Cooled Lithium–Lead (WCLL) is one of the most promising technologies for power conversion and tritium production in future fusion-powered reactors; it will be implemented in one of the Test Breeding Modules (TBM) inside the ITER reactor and the DEMO EU reactor. However, the simultaneous presence in the system of high-temperature PbLi and high-pressure water poses significant safety issues in the event of an in-box LOCA (Loss Of Coolant Accident). For this reason, a complete understanding of the system response is crucial to avoid extensive damage in such a scenario. This paper describes the status and design features of the LIFUS5/Mod4 facility, an experimental plant that is currently being designed and constructed at ENEA CR Brasimone in the framework of the FP9 EUROfusion Horizon Europe to address these issues. This facility aims at being representative of the geometry and operational conditions of the Test Breeding System (TBS) to allow the precise reproduction of its behavior under simulated incidental scenarios. For this reason, peculiar design choices have been made, which will be extensively discussed throughout this work and which will allow the generation of high-quality data useful for the TBS development. Moreover, the facility is expected to become a test stand for the implementation of different safety functions, to identify the best accident-mitigation strategy. Possible upgrade plans for the facility are described as well, with the chance for it to become a fully functional test stand for any component of the TBS in their operative conditions.

In the framework of the ITER (International Thermonuclear Experimental Reactor) project, one of the key components of the reactor is the ECRH (Electron Cyclotron Resonance Heating). This system has the duty to heat the plasma inside the tokamak, using high frequency and power radio waves, produced by sets of 1MW gyrotrons. One of the main issues related to the gyrotron operation is the output power drop that happens right after the beginning of a pulse. In this work, we study the underlying phenomena that cause the power drop, focusing on the gyrotron’s MIG (Magnetron Injection Gun) of the 1MW, 170 GHz European Gyrotron prototype for ITER. It is shown how the current emission and the temperature of the emitter are tightly bound, and how their interaction causes the power drop, observed experimentally. Furthermore, a simple yet effective lumped-parameter model to describe the MIG’s cathode thermal dynamics is developed, which is able to predict the power output of the gyrotron by simulating the propagation of the heat inside this component. The model is validated against test results, showing a good capability to reproduce the measured behavior of the system, while still being open to further improvements.

The in-box LOCA (Loss of Coolant Accident) represents a major safety concern to be addressed in the design of the WCLL-BB (water-cooled lead-lithium breeding blanket). Research activities are ongoing to master the phenomena and processes that occur during the postulated accident, to enhance the predictive capability and reliability of numerical tools, and to validate computer models, codes, and procedures for their applications. Following these objectives, ENEA designed and built the new separate effects test facility LIFUS5/Mod3. Two experimental campaigns (Series D and Series E) were executed by injecting water at high pressure into a pool of PbLi in WCLL-BB-relevant parameter ranges. The obtained experimental data were used to check the capabilities of the RELAP5 system code to reproduce the pressure transient of a water system, to validate the chemical model of PbLi/water reactions implemented in the modified version of SIMMER codes for fusion application, to investigate the dynamic effects of energy release on the structures, and to provide relevant feedback for the follow-up experimental campaigns. This work presents the experimental data and the numerical simulations of Test E4.1. The results of the test are presented and critically discussed. The code simulations highlight that SIMMER code is able to reproduce the phenomena connected to PbLi/water interaction, and the relevant test parameters are in agreement with the acquired experimental signals. Moreover, the results obtained by the first approach to SIMMER-RELAP5 code-coupling demonstrate its capability of and strength for predicting the transient scenario in complex geometries, considering multiple physical phenomena and minimizing the computational cost.

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