A Neutron Measurement System Design for Pulsed Triga Reactor Experiment at Texas A&M University

Abstract

This thesis focuses on designing, building, and analyzing a neutron detection system to measure neutron fluxes of a TRIGA reactor at Texas A&M University to verify newly developed simulation codes. Such a system must be designed to cover a wide range of neutron fluxes in transient power surges (up to 1015 neutrons/cm2/s, lasting 20 to 50 ms) and in steady-state operations (1013 neutrons/cm2/s at full power of one megawatt). The size of the detector is limited to a maximum of 9.525 mm outer diameter including housing. The detection system consisted of slow neutron detectors, associated electronics, data acquisition and storage equipment, and an analysis software. The detector used boron- 10 to capture slow neutrons, generating charged particles within an ionization chamber filled with air. Due to the low Q-value of the reaction, a high gain charge-sensitive preamplifier, which was a part of a miniature 16.9 mm x 298.5 mm electronic package, was placed within 1.7 m of the detector to minimize noise level. The preamplifier was designed to offer pulse mode, current mode, and high voltage current mode of operation. Experimental data were acquired at 20 MHz using a solid-state drive for data storage and were subjected to 250 MHz for up to eight-hour continuous operation using an array of five three-TB hard drives. Data analysis software was programmed using MATLAB. In addition to analysis using the shaping amplifier’s output, an algorithm to generate a radiation pulse from the directly digitized preamplifier signal was proposed and tested with test pulses simulating neutron events. The detection system was tested with isotopic sources and in a dry tube located near the TRIGA reactor. The latter showed an increase in the number of gamma events with the reactor power, whereas the number of neutron events was also proportional to the power. In addition, a trial run of in-core measurements was performed. The results suggested that high gamma radiation present in the core interfered with the neutron signal. Suggestions was made for modification of the mechanical assembly of the system, compensation for gamma signals, and additional tests to improve analysis of the neutron signal.