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

During the physical start-up of the IVG.1M research reactor, which involved the conversion to low-enriched uranium fuel, various studies were conducted using physical mock-ups of the fuel assemblies. The mock-up consisted of 468 model low-enriched uranium fuel elements that were cut into three sections without end coatings at the cut locations. This configuration allowed for the simulation of fuel element decompression and the experimental determination of fission product release into the coolant. The coolant samples obtained from the mock-up were analyzed using a gamma-spectrometer equipped 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 product release were determined. The relative release is defined as the ratio of the release rate of reference fission products to its birth rate. For the first time, fission product release was experimentally obtained in a situation simulating the decompression of IVG.1M fuel cladding.

Experimental studies of power distribution in LEU-fuel of the IVG.1M reactor.

For the past ten years, the IVG.1M research reactor has been converted from high-enriched uranium (HEU) fuel to low-enriched uranium (LEU) fuel. Currently, the final stages of the IVG.M reactor conversion, including physical and energy start-ups, are underway. As part of the physical start-up, one of the objectives was to conduct physical studies on the power distribution across the radius and height of the fuel assemblies in water-cooled technological channels. Studies were carried out using the activation gamma-spectrometric method based on correspondence between energy release and measured gamma-radiation activity of fission or activation products. The ENREDI program was used to determine the detailed relative power distribution over radial cross section of fuel assembly. During these experimental studies, relative power distribution along the height and radial cross section of the IVG.1M fuel assembly, as well as power peaking factors were obtained. These studies will make it possible to evaluate the changes in the IVG.1M reactor fuel power profile after the fuel enrichment reduction, and to verify the accuracy of neutronic simulations.

Methods to study power density distribution in the IVG.1M research reactor after conversion.

In the Republic of Kazakhstan, within the framework of international initiatives on the non-proliferation of nuclear weapons, the IVG.1M research reactor is being converted to low enriched fuel. Due to the change in the fuel composition, it becomes necessary to assess the power density distribution in the fuel assemblies and in the core altogether. Close attention to this parameter is explained by the fact that the non-uniformity of the radial and axial power density fields determines the operating parameters of the reactor, its power, the core resource and the efficiency of fuel utilization. The purpose of this work is approbation of the activation gamma-spectrometry method for determining the power density distribution in the fuel of the IVG.1M research reactor after conversion. Additionally, for a preliminary assessment of the experimental outcomes, the paper presents the MCNP6 calculation results for the power distribution in fuel assemblies and the peaking factors.