Manufacturing of an Iridium-192 Ionizing Radiation Source for Nondestructive Testing

Abstract

The optimal modes of irradiation of metal disks of natural iridium with thermal neutrons from the VVR-SM reactor were found, and the ¹⁹²Ir radionuclide with a high specific activity (up to 250 Ci/g) was obtained. The flux of thermal neutrons and their distribution along the vertical channel were determined using a TND-2.0 thermal neutron detector and ⁵⁹Co monitors in the form of a foil disk (∅ = 3.0 mm, h = 0.2 mm, m = 3.0 mg) containing an Al–⁵⁹Co (0.01%) alloy. The maximum values of the potential difference and thermal neutron fluxes are observed 35–45 cm below the top point of the vertical channel (or 35–45 cm below the top point of the IRT-4M fuel assembly head). The observed high values of cadmium ratios show that neutron activation of natural iridium is mainly due to thermal neutrons. With an increase in the thickness of the iridium disk, the yield of the induced activity of ¹⁹²Ir decreases. Packages of natural iridium disks were irradiated with thermal neutrons in the vertical channel of the reactor and radiochemically processed, and ¹⁹²Ir ionizing radiation sources with an activity of 50–20 Ci were manufactured and leak-tested by the immersion method. A nondestructive test of the welding quality of a metal pipe with a diameter of 219.0 mm and a wall thickness of 8.0 mm with a welded seam, carried out with an ¹⁹²Ir radiation source through two walls, showed a good result, and the obtained gamma-ray images matched in terms of sensitivity and quality the requirements of GOST-7512-82 “Nondestructive Control. Welded Joints” (Russia) and ASME (USA). ¹⁹²Ir sources with Gammarid-192/120M gamma-ray flaw detectors were used for nondestructive testing of the quality of welded seams of pipelines at the construction sites of the Talimarjan and Takhiyatash thermal power plants and the Kandym Gas Processing Plant of the Republic of Uzbekistan.