Analysis of vanadium Self Powered Neutron Detector’s signal

Abstract

Self Powered Neutron Detectors (SPNDs) have been widely used for monitoring the neutron flux, either in Nuclear Power Plants (NPPs) as well as in irradiation facilities and medical treatments. Nevertheless, the physical meaning of the parameter used to relate the detector signal (an electric current) to the neutron flux, i.e., the detector sensitivity, was not sufficiently analysed. Since the sensitivity, defined as ∊=iϕ, is calculated for given reactor conditions, thermal neutron flux at room temperature, it does not take into account the deviation originated at higher temperature conditions, like are found in nuclear reactors at NPPs, for example. The aim of this work is to explicitly exhibit the nonproportionality between the detector current signal and the neutron flux at different temperatures. The calculation of the neutron flux weighted microscopic cross section, definedσˆ=∫dεσϕ∫dεϕ,for a temperature interval has revealed the nonconstant behaviour of the sensitivity as a function of the temperature, showing the problem that SPNDs have to represent the neutron flux of a nuclear reactor at a NPP. As a consequence of this fact, it is not possible to use the sensibility as an absolute constant, but rather it must be calculated for each nuclear reactor and corrected under determined conditions.