Instrument for continuous supervision of the radioactivity of CO2 coolant in piles - DCCA -CO2 (1960)

This paper describes an apparatus for continuous measurement of CO2 activity, which can be used on piles cooled by circulation of gas. The first part is devoted mainly to describing the apparatus used and the character of the radioactivity and thermodynamic measurements carried out, and giving the general characteristics of the gas circuit required if the instrument is to be suitably gas-tight. In the second part theoretical calculations are given, particularly on the determination of the ionisation current in an ionisation chamber with circulating gas. Several parameters enter into this determination, such as the mean path of β particles in the ionisation chamber, the linear number of ion pairs formed in the gas by these β particles as a function of their energy, the temperature and pressure of the gas in the ionisation chamber. This part also evaluates the sensitivity areas of the apparatus for measuring the concentrations of radioactive gases such as argon-41 and fission gases from uranium-235 in the CO2 coolant. In the last part are described the results of measurements performed with such an apparatus on the pile EL2, the special investigations carried out on the CO2 coolant of this pile, and the information gained during normal operation and during accidents. The DCCA - CO2 which has just been put in operation at G2 is briefly presented. In the conclusion the possibilities offered by this apparatus are underlined. (author)