Developed Data Acquisition System Research Articles

Measurement and analysis of low energy neutron spectrum in a large cylindrical iron assembly bombarded by D- T neutrons

The experimental measurement of low energy neutron spectra in a large iron assembly is essential to examine nuclear data and neutron transport codes for nuclear heating estimations in the superconducting magnet of a fusion reactor as well as shielding design. In-situ neutron spectra between a few keV and 1 MeV in a 0.95 m thick cylindrical iron assembly, bombarded with D-T neutrons, have been measured, using a proton recoil gas proportional counter (PRC). A newly developed data acquisition system for PRC was adopted, where high voltage varies continuously in ramped shape during acquisition. Experimental analyses were performed by the DOT3.5 and MCNP codes with cross section sets based on the JENDL-3 nuclear data library. From the comparison between the measured and calculated neutron spectra, the following facts were obtained. The calculation by DOT3.5 overestimated the experiment by a factor of about 2 for the flux below 500 keV in the front parts of the iron assembly and underestimated by more than a factor of 2 for the flux above 500 keV in the rear parts. The calculation by MCNP gave a general agreement with the measurement, but the discrepancy above 100 keV increased as the detector position moved deeper into the assembly. The calculation above 500 keV underestimated the measured spectrum by more than 30% at the 0.81 m depth.