Characterization of Low Level Wastes: a new design for calorimetric measurement

Kévin Galliez,Alain Godot,Christophe Mathonat,Guillaume Jossens,A Lyoussi,M Giot,P Le Dû,M Schyns,L Vermeeren,C Reynard-Carette,M Carette

doi:10.1051/epjconf/201817007003

Abstract

Calorimetry is one of the best solutions to estimate the overall quantity of nuclear material on a wide range of masses, from a few milligrams up to kilograms of radionuclides, by measuring the overall thermal power due to the radioactive decay coming from the waste contained in a metallic drum or a different type of container. It has many advantages as it features a non-destructive method which remains independent of matrix effect or the chemical composition. Until now, calorimetry allows to measure at the lowest 0.5 to 1 mW for samples up to 385 liters. But nowadays, thanks to new technological breakthroughs, KEP-Technologies calorimeters are able to measure as low as 50 μW for 40 liters samples. The μLVC is based on a new design with twin cells, a new temperature regulation loop and a heat-flow measurement system inside a vacuum chamber (Patent deposit P005299 LA/VL). The μLVC is a differential heat-flow calorimeter for precise measurement independent of the residual fluctuations caused by environmental changes. The new calorimeter is an industrial product able to work in environmental conditions with wide temperature variations. The first results have shown a great improvement in the detection of very low thermal effect thanks to the thermal noise reduction. The paper presents the developments in Large Volume Calorimetry as a new tool for quantification of nuclear material to characterize Pu-Am samples, i-graphite, and low tritium samples with high precision and reliability.

Highlights

Calorimetry is used as a non-destructive assay technique to determine alpha or beta emitters inventories
It is one of the best solutions to estimate the overall quantity of nuclear material on a wide range of mass, from a few milligrams up to kilograms of radionuclides with a good precision
The advantage of calorimetry towards other techniques is that the measurement is independent of the matrix, only the thermal conductivity of the sample matters, which influences the measurement time

Summary

INTRODUCTION

The calorimetric signal results from the measurement of the heat flow between the measurement cell containing the radioactive sample and the thermal block. The temperature of the thermal bloc is maintained constant thanks to resistive heater This thermal heat flow generates a signal (μV) based on time which is recorded by a data acquisition system. The heat flow between the calorimetric bloc and a mass of high thermal inertia - which serves as a reference of temperature - is regulated. The signal coming from the thermopile is kept constant and close to zero in order to bring the calorimeter at its thermal equilibrium This principle allows achieving high temperature stability and a very precise regulation. The heat flow generated between the sample and the thermal block is measured and can be compared with the heat flow measured between the reference cell and the calorimetry block. The use of several Peltier modules for the same measurement of a heat flow makes it possible to increase the sensitivity of the measurement

Thermal bloc Insulation chamber External bloc

RESULTS AND DISCUSSION

Si with

TABLE I DETECTION LIMITS FOR COMMON RADIONUCLIDES USING THE μLVC