Improvement of the quality of neutron radiography beamlines in Isfahan MNSR

Abstract

Recently, two external neutron beam lines have been installed in the Isfahan MNSR. This reactor is a tank in pool type with a maximum power of 30 kW, which has been in operation since 1994, and in its original design it did not have a beam tube. These two neutron beam lines are designed and installed out of the reactor tank for irradiation experiments of large objects outside the reactor core, such as neutron radiography. The results of the evaluations in the previous researches showed that these two beam lines have acceptable quality according to the ASTM-E545 standard. However, their gamma contamination were relatively high. In this study calculations and experiments have been done to reduce the gamma content of the neutron beams and to increase the ratio of thermal neutron flux to gamma dose rate. This was done through the design and installation of gamma filters in the beam lines. The results of the evaluations showed that the quality of the neutron beams has been greatly improved in terms of reducing gamma content, so that the quality rating of the beams has increased by at least two ranks.