Tests and Foreseen Developments of Fibered-OSLD Gamma-Heating Measurements in Low-Power Reactors

Abstract

Abstract-In this paper are presented test measurements of a fibered-OSLD system performed during a dedicated experimental phase in EOLE zero-power reactor. The measurement setup consists of an OSLD crystal connected onto the extremity of an optical fiber and a laser stimulation system, manufactured by the CEA/LIST in Saclay. The OSL sensor is remotely stimulated via an optical fiber using a diode-pumped solid-state laser. The OSL light is collected and guided back along the same fiber to a photomultiplier tube. Results obtained using this system are compared to usual gamma heating measurement protocol using OSLD pellets. The presence of induced radio-luminescence in the OSLD during the irradiation was also observed and could be used to monitor the gamma flux.The feasibility of remote measurements is achieved, whereas further developments could be conducted to improve this technique since the readout procedure still requires to withdraw the OSLD off the gamma flux (hence from the core) on account of the dose rate (around a few Gy.h -1 ), and the readout time remains quite long for on-line applications. Several improvements are foreseen, and will be tested in the forthcoming years.Index Terms-nuclear heating, optical fibers, optically stimulated luminescent dosimeters, remote readout I. INTRODUCTION HE accurate determination of nuclear heating in materials is a major issue for the development of nuclear technology and in particular the design of new core concepts, such as the Jules Horowitz material testing reactor [1].In material testing reactors the neutron and gamma flux levels allow to measure directly the nuclear heating by calorimetry based techniques for instance. In mock-ups or zero-power reactors (ZPRs), such as EOLE and MINERVE reactors at Cadarache [2], the low operating level -typically from some watts to some kilowatts -requires the use of different methods such as dosimetry. In the past few years, several experimental programs [3][4] were devoted to the improvement of gamma heating measurements using thermoluminescent and optically stimulated luminescent dosimeters (TLDs and OSLDs, respectively). However, the main drawback of nuclear heating measurement in low-power reactors remains the off-line gamma heating estimation, given that both TLD and OSLD stimulations (thermal and optical respectively) allowing the readout of the absorbed doses can only be performed after irradiation and out of core. To circumvent this disadvantage, an effort is being made on the development of in situ and on-line measurement of the gamma heating. One of the considered solutions is the use of optical fibered systems.In the first section are presented the main principles of gamma heating measurements in low-power reactors, and especially the system that was used for. In the second section are presented the results of test measurements performed in the EOLE reactor. II. GAMMA HEATING MEASUREMENTS USING OPTICAL FIBERS A. Overview and general principlesNuclear heating in material arises from the local deposition of energy carr...