Experimental studies of fission product release from model fuel rods at the physical start-up of the IVG.1M research reactor

During the conversion of the IVG.1M research reactor to low-enrichment fuel, various studies were conducted with a physical mock-up of a water-cooled technological channel. One of the points of the study was to assess the release of fission products by sampling coolant from a physical mock-up of a water-cooled technological channel. The fuel assembly of the physical mock-up consists of 468 model low-enriched uranium fuel rods, which are cut into three sections (upper, measuring, and lower) that have no end coating in the cut locations. This made it possible to simulate the decompression situation and experimentally determine the release of fission products into the coolant. The fuel element of the IVG.1M reactor is a spiral rod with a two-blade profile with a core of U-Zr fuel, a zirconium cladding, and a nickel end coating. The core is a matrix of zirconium with axially oriented uranium filaments placed in it. The coolant samples were measured by gamma spectrometry using a gamma-spectrometer with a high-purity germanium detector. As a result of the studies, the activities of fission products in the coolant and the averaged relative fission products release, which is the ratio of the release rate of the reference fission products to their birth rate, were determined. For the first time, fission product release was experimentally obtained in a situation simulating an accident with decompression of fuel cladding. (author)