OSIRIS REACTOR - Centre de Cadarache - CEA

EXPERIMENTAL DEVICESNUCLEAR ENERGY AUTHORITY ••• CEA29Qualificationof the instrumentationThe qualification under irradiation ofthe instrumentation is a crucial stageof its development. This qualificationconcerns for example: the mobile calorimetry device, whichcan measure the nuclear heating in allthe experimental positions of OSIRIS.This tool enables a vertical examinationover the entire height of the core andthe upper parts of the irradiationdevices, the pressure transmitter of fissiongases, the new type of high-temperaturethermocouple containing molybdenumand niobium, designed and developedspecifically by the CEA in closecooperation with an industrial specializedin thermometry for the nuclear powerindustry.QUALIFICATION OF THERMOCOUPLESAT HIGH TEMPERATUREHigh temperatures (above 1200°C) during the irradiation ofmaterials or fuels are measured using C-type thermocouples.The prolonged use of C-type thermocouples (W/Re) undera neutron flux induces a drift caused by an irreversible modificationin their thermoelectric capacity because of the transmutationof metals constituting these couples.Mo/Nb thermocouples have a response similar to thoseof other couples of the C type and in theory are not affected bythe phenomena of transmutation. Qualification of the Mo/Nbthermocouples consists in quantifying their drift under flux andat high temperatures in relation to the fluence receivedand to compare it with that other couples of the C or K type.The fixed point principle (the melting point of copper) is used tomeasure the change in the signals caused by the neutron fluence.The thermocouples are inserted into a graphite core in a copperreceptacle equipped with heating elements. The assembly isembedded in a graphite barrel and introduced into an irradiationdevice of the CHOUCA type.QUALIFICATION OFA PRESSURE PICK-UPThe qualification in operation underirradiation of the “backpressure”pressure pick-up takes place whilemounting the sensor on a false fuelelement, the internal pressure of whichis controlled and measured via apressurized circuit. Qualification isbased on the comparison between thepressure injected into the fuel elementand that provided by the sensor.The performance characteristics aretested at high temperature andthroughout the effective range.Because of its design, no drift inmeasurement in the nuclearenvironment is observed.Sensor measurment (bar)Zoomed areaInjected fuel rod pressure (bar)