International audienceNuclear heating measurements in Material Testing Reactors are crucial for the design of the experimental devices and the prediction of the temperature of the hosted samples. Indeed, nuclear heating is a key input data for the computer codes which simulate temperature reached by samples under irradiation. In the Jules Horowitz Reactor under construction at the CEA Cadarache, the maximal expected nuclear heating levels will be about 15 to 18 W/g and it will be necessary to measure this key parameter with the best accuracy. An experiment was led at the OSIRIS reactor to compare the measurements between the two most appropriate sensors for measuring nuclear heating in MTR; a differential calorimeter and a gamma thermometer. A specific differential calorimeter was designed for low nuclear heating and a standard gamma thermometer was used. Experimental results and Monte-Carlo simulations show that the two sensors are suitable even if the measured energy deposit is different in the two sensors. Finally, these comparisons between the measurements recall that it is primordial to precise in which material and environment the nuclear heating is measured to use this key parameter for designing experimental devices in MTR

Abstract-The nuclear radiation energy deposition rate (unit usually employed: W.g -1 ) is a key parameter for the thermal design of experiments on materials and nuclear fuel carried out in experimental channels of irradiation reactors, such as the French reactor in Saclay called OSIRIS or the Polish reactor named MARIA. In particular the quantification of nuclear heating allows the prediction of heat and thermal conditions induced in irradiated devices and/or structural materials. Various sensors are used to quantify this parameter, in particular radiometric calorimeters, also known as in-pile calorimeters. Two main kinds of in-pile calorimeter exist possessing two geometries and two measurement principles: the single-cell calorimeter and the differential calorimeter. The present work focuses on specific examples of these calorimeter types, from the step of their out-of-pile calibration (transient and steady experiments respectively) to the comparison between numerical and experimental results obtained from two irradiation campaigns (French and Polish reactors). The main aim of this paper is to propose a steady numerical approach to estimate the single-cell calorimeter response under irradiation conditions.

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Four grades of commercial PZT materials have been exposed to nuclear radiation during five months in an irradiation channel of the BR1 research reactor at SCK•CEN (Belgium). This experimental study was performed in the framework of the Joint Instrumentation Laboratory with the CEA French Commission of Atomic Energy to validate these materials for future applications in severe conditions such as online measurements in irradiation experiments performed in research reactors. For this purpose, thin piezoelectric discs were irradiated while a remote network analyser continuously monitored the frequency response of their electrical impedance. The total neutron dose has reached a level of 1.5.10 17 neutrons/cm 2. Positive and negative shifts of the peak resonance frequency have been recorded but in any case with a variation lower than 1%. On the other hand, the amplitude of the electrical impedance at resonance frequency has largely decreased with even a reduction by factor two or three for some piezoelectric cells. Transitory effects have also been detected for these two parameters as function of the reactor activity. Additional thermal and gamma radiation effect have been investigated. Similarly, some piezoelectric cells glued on glass delay line have been tested with satisfactory results to these stresses.

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