Qualification of an out-of-pile Thermohydraulic test Bench (BETHY) developed to calibrate calorimetric cells under specific JHR experimental conditions

Online in-pile measurement methods are crucial during irradiations in material testing reactors to better understand the behavior of materials under accelerated ageing conditions and of nuclear fuels under high irradiation levels. Thus, the construction of a new Material Testing Reactor such as the Jules Horowitz Reactor (JHR) leads to new research and development programs devoted to innovative instrumentation and measurement methods. The presented works are performed in the framework of the IN-CORE program, 'Instrumentation for Nuclear radiations and Calorimetry Online in Reactor', between CEA and Aix-Marseille University. The program aim is to develop experimental devices and test bench to quantify more precisely the nuclear heating parameter in the JHR experimental channels. This in-pile parameter is usually measured by means of calorimeter or gamma thermometer. This paper focuses on a new out-of-pile test bench called BETHY. This bench was developed to study the response of a differential calorimeter during its preliminary calibration step according to specific thermal and hydraulic conditions occurring inside one type of JHR core channel. The first section of this paper is dedicated to a detailed description of the bench. The second part presents the study of the thermal characteristics established in the bench for two main thermal running modes. The last one concerns the calibration curve of the reference cell of the differential calorimeter in the case of homogenous temperature. (authors)