Measurement of the Neutron Spectrum inside the Containment of a PWR

Abstract

Abstract Neutron spectra inside the containment building of a PWR at Gosgen, Switzerland have been measured using a high resolution, transportable, neutron spectrometry system based on proportional counters. Small spherical proportional counters, filled with hydrogen to pressures of 100, 300 and 1000 kPa, were used to cover the energy range from 50 keV to 1.5 MeV. A larger cylindrical counter, filled with 600 kPa of 4He plus 400 kPa Ar was used to extend the measurement range up to 16 MeV. Compact electronics provided simultaneous data acquisition for up to four counters allowing spectrum measurements to be performed in dose equivalent rates down to ~50 µSv.h-1. Supporting measurements were made with a multisphere spectrometer to determine the fraction of neutrons below 50 keV. The neutron spectra measured at two positions show a steady rise in the neutron fluence as the neutron energy decreases, with very few neutrons having energies above 700 keV.