Development of the DNAA System for Screening Environmental Samples to Measure fissile Material

The DNAA system made up of pneumatic transport system, neutron detector assembly, and signal processing equipment was installed in the High-flux Advanced Neutron Application Reactor (HANARO). The optimized position of the detector in the delayed neutron counting (DNC) system was evaluated at a distance 15.1 cm from center of the DNC system with 18 He-3 detectors using MCNP simulation. The system shows excellent linearity from 0.67 ng to 713 ng U-235, and reproducibility of 1.26% standard deviation for the various mass groups of U-235 samples. The DNAA system shows detection efficiency of ~30 % and U-235 detection limit of 1ng. This system can be used on a screening method to assist the environmental sample analysis and to protect the clean room from elevated levels of fissile material that might be in routine samples.