The design and construction of a collimator holder to equip beam tube D of the Tehran research reactor

Abstract

The continued safe and efficient operation of a research reactor depends on the behavior of the structural materials making up its main components. Many of these materials are difficult to replace in view of hard-to-reach locations after installation or even storage after years of use due to radiation from high exposure to neutrons inside the research reactor structure. The neutron collimator is a major part of the beam-related devices used in a research reactor. This device is installed in the beam tube via a holder. The collimator holder used as a structural component of beam tube D in the Tehran Research Reactor (TRR) has been made of cast iron. This component has been installed inside the beam tube and subjected to irradiation for 30 years. As a result, it has become severely damaged and must be transferred to radioactive waste storage. A necessary measure to recommission beam tube D in TRR is selecting a replacement with higher quality. Suitable candidates for this purpose would be materials that retain the neutron beam quality in addition to being adequate for long lifetime management. In this case, lower induced activity, shorter half-life of produced radioisotopes, and shorter cooling time are desirable. The present work used ORIGEN2 and MCNPX2.6 computational codes to compare various materials, such as barite concrete (type BA), Portland iron concrete, and stainless steel (316), in terms of the induced activity for various reactor operation periods, radiation level for various cooling periods, and neutron and photon beam parameters at the beam tube nozzles. The results indicated that replacing cast iron with Barite concrete (type BA) retains the quality of the neutron beam. In addition, 11.2, 2.81, and 3.63 times more activity was induced in stainless steel, Portland iron concrete, and cast iron, respectively, compared to type-BA barite concrete after 30 years under identical conditions. Since barite concrete is economical and simpler to manufacture, it was a suitable replacement for cast iron as the material for the collimator holder in beam tube D in TRR. In addition, Barite concrete holder was constructed based on the calculations made in this research. The results showed a good agreement between dosimetry experimental data and calculation results with a 3 % error.