Experimental and numerical investigation of SGTR event for HLM reactors

In the framework of EC funded THINS, LEADER and MAXSIMA projects the water/LBE interaction was investigated experimentally and numerically, aiming to improve the knowledge of the physical behaviour and the understanding of the postulated SGTR event, in relevant configurations for HLMFRs. Two experimental campaigns were carried out in the separate effect LIFUS5/Mod2 facility at ENEA CR Brasimone. Ten tests THINS were performed aiming to characterize the water/LBE interaction injecting water at 16 and 40 bar into a pool of 100 L partially filled by LBE at 400°C. The experiments showed low pressure peaks at the injection instant and final pressurizations comparable to that of injection. The vapour cloud into the melt was mapped according to the temperature field by thermocouples. Seven tests LEADER studied the water injection (180 bar) in the centre of a tube bundle of 188 tubes, immersed in LBE at 400°C, for studying the effect of the SGTR event in the spiral tube steam generator of ELFR. The domino effect on the surrounding tubes did not occur. High quality data were acquired during both THINS and LEADER campaign for code validation and database enlargement. A post-test analysis of the overall THINS campaign was performed by the SIMMER-III code, highlighting the importance of the two-phase flow in the injection line, the code capabilities of simulating the pressurization transient, final plateaux in the reaction vessel, injected water mass flow rate and code limitations. The first test of the LEADER was numerically investigated by SIMMER-III code on the base of the initial condition provided by the RELAP5-3.3 calculations. It showed the importance of the phenomenology occurring in the injection line and the prediction of the first pressure peak in agreement with the experimental data, besides the pressurization transient and injected water. The design of a test section to be implemented in CIRCE facility at CR Brasimone, simulating a full scale portion of the primary heat exchanger of MYRRHA reactor, was carried out for analysing the postulated SGTR scenario. Four tests were scheduled to be performed, studying two different positions of tube rupture. A preliminary pre-test analysis, of the SGTR event in CIRCE facility, was carried out by SIMMER-III code on the base of a simplified test section configuration. It provided useful data (e.g. number and size of rupture disks, grace period without safety system activation, cover gas volume) for the execution of the final design of the test section. The design was completed and on its final configuration the pre-test analysis was performed by a complex model realized adopting the 3D SIMMER-IV code. Both the SGTR scenarios were simulated, guarantying safe execution of the experimental tests. The test section construction was completed and the execution of the experimental run will be accordingly the time schedule.