Conducting in-reactor studies of objects the length of which exceeds the height of the IVV-2M reactor core

Abstract

When solving several research problems, the need arises for reactor testing of non-standard objects. The IVV-2M reactor is a pool, heterogeneous, light-water reactor. The 500 mm-high reactor core comprises six sections of six fuel assemblies (FA) with central water traps and a water trap in the center of the core. The personnel of INM JSC were tasked with testing an object whose length exceeded the height of the IVV-2M reactor core. A non-standard core layout was developed with six sections of seven fuel assemblies to accomplish this task.. The test object is located in the center of the core, surrounded by special aluminum blocks. Several fuel assemblies are installed on special supports, which allow the fuel assemblies to be installed 200 mm higher. Shim rods have been moved to the center of the sections. The safety of the developed arrangement was confirmed by neutron-physical calculations using the certified MCU-PTR software tool. Calculations have shown that the maximum maximum power in the fuel assembly is 236 kW, which is 50% less than the permissible value. To confirm the safety of the layout and ensure the required test conditions, tests of a mock-up of the object were carried out. The efficiency of the control members was experimentally determined. The overall efficiency of the control members was 4.85% ∆k/k, the physical weight of the object was 1.46% ∆k/k. Based on the requirements of the Nuclear Safety Rules for Research Reactors, the test duration is no more than three days. The distribution of neutron flux density over the height of the core was determined using indium neutron activation detectors. The developed design solutions made it possible to form a unique IVV-2M reactor core layout for testing objects exceeding its height.. Neutron-physical calculations and tests of the irradiated device mock-up confirmed the safety and performance of this core arrangement.