• HTHL facility
• RELAP5
• Helium
• Thermal-hydraulics

The present work is focused on the thermal-hydraulics analysis of the active channel of the HTHL facility located in Research Center Rez in Czech Republic. The High Temperature Helium Loop (HTHL) facility is designed to offer, in laboratory conditions, analyses of materials under the combination of high temperature gas environment and gamma irradiation effects.
The introduction provides the general structures of the works and the overview of the facility in the framework of the Generation IV. Subsequently the description of the facility is reported with a particular emphasis of the active channel and its major components.
Specific attention has been focused in studying the models used by RELAP5 code for implementing the helium as noncondensable gas. Furthermore, it has been evaluated an alternative solution in order to demonstrate the feasibility of the code for performing calculations with helium as main fluid.
After simplified assessment of the capability of the code, the nodalization of the active channel was developed.
Several calculations have been performed using the RELAP5/Mod3.3js version code owned by U.S. NRC. A preliminary analysis was conducted to obtain the steady state data of the active channel in both configurations (out of pile and in-pile). Subsequently, the results of the steady state have been used as starting conditions for the analyses of several scenarios. In particular, a set of transients representative of operational and accidental conditions, which are particular meaning to draw up the operational procedures of the HTHL facility and for future improvements of the design, were performed.
Nowadays, the facility is currently constructed for out of pile configuration and, at the end of September 2015, the in-pile configuration should be concluded with the insertion of the loop inside the research reactor LVR-15 hosted in Rez.