Shielding Design Optimization of the HANARO Cold Neutron Triple-Axis Spectrometer and Radiation Dose Measurement

Abstract

A new cold neutron triple-axis spectrometer (Cold-TAS) was recently constructed at the 30 MW th research reactor, HANARO. The spectrometer, which is composed of neutron optical components and radiation shield, required a redesign of the segmented monochromator shield due to the lack of adequate support of its weight. To shed some weight, lowering the height of the segmented shield was suggested while adding more radiation shield to the top cover of the monochromator chamber. To investigate the radiological effect of such change, we performed MCNPX simulations of a few different configurations of the Cold-TAS monochromator shield and obtained neutron and photon intensities at 5 reference points just outside the shield. Reducing the 35% of the height of the segmented shield and locating lead 10 cm from the bottom of the top cover made of polyethylene was shown to perform just as well as the original configuration as radiation shield excepting gamma flux at two points. Using gamma map by MCNPX, it was checked that is distribution of gamma. Increased flux had direction to the top and it had longer distance from top of segmented shield. However, because of reducing the 35% of the height, height of dissipated gamma was lower than original geometry. Reducing the 35% of the height of the segmented shield and locating lead 10cm from the bottom of the top cover was selected. After changing geometry, radiation dose was measured by TLD for confirming tester's safety at any condition. Neutron(0.21 μSvhr -1 ) and gamma(3.69 μSvhr -1 ) radiation dose were satisfied standard(6.25 μSvhr -1 ).

Improved monochromator concrete shielding for the cold neutron triple-axis spectrometer at HANARO

“…The segmented shield structure of the cold-neutron triple-axis spectrometer (Cold-TAS) was improved, and the sample table and analyzer were simplified in 2013 [2,3]. The concrete shield was transformed downward because of the weight of the segmented lead shield.…”