RELAP 5 pre-test analysis on the HELENA facility for operational transients

This work concerns the thermal-hydraulic pre-test analysis carried out to study the operational transients of the HELENA facility, designed at ENEA Brasimone Research Centre to qualify the structural material proposed for the impeller of the centrifugal pump foreseen in LFRs. The simuiations were pertormed using a version of the RELAP5/Mod.3.3 code purposely modified to account for Iead properties and behavior. In the first part of the work the general characteristics of the nodalization set-up for the HELENA loop are described, trying to give particular attention to the implementation of the pump component. The second part of the activity deals with the analysis of results obtained by the code in relation to two different operational transients characterized by the different value of the friction loss coefficient of the calibrated orifice present inside the primary loop. The obtained results suggest a possible start-up procedure of the HELENA facility and a first indication of its thermal-hydraulic behaviour.