Water velocity determination in the gaps of irt-3M, -4M fuel assemblies

Abstract

Experiments on measuring the water velocity in the gaps between the fuel elements of an IRT-3M eight-tube fuel assembly with 90% fuel enrichment, used in pool and tank research reactors, are described. The experiments were performed on a hydraulic facility at the National Research Center Kurchatov Institute. The velocity was determined from the dynamic head in the gaps of a model fuel assembly. These velocities were used as a basis for determining the water flow rate in each gap and the total flow rate through a fuel assembly. Comparative hydraulic calculations of IRT-3M fuel assemblies with 90% fuel enrichment and IRT-4M fuel assemblies with 19.7% enrichment, developed as a replacement for IRT-3M, are described. It is shown that if the IRT-4M gaps decrease to 1.85 mm, then the water velocity in them will decrease by only 5% as compared with IRT-3M.The development in 1963 of tubular fuel elements with a square cross section for the IRT subsequently continued to improve. Initially, the IRT-M fuel assemblies consisted of three tubes [1]. The fabrication of four-tube IRT-2M fuel assemblies was perfected in 1968 [2]. The IRT-3M fuel assemblies for pool and tank IRT and VVR-S research reactors were developed by 1979 to replace IRT-2M fuel assemblies with fuel assemblies having an extended heat-emission surface [3]. These fuel assemblies with 90% fuel enrichment were first used as regular assemblies in the IR-8 at the Kurchatov Institute in 1981 and subsequently in the IRT at the Moscow Engineering-Physics Institute (MIFI) and IRT-T in Tomsk. Later, a modification of these assemblies was developed with fuel enrichment 36%, which started to be used in VVR-SM in Tashkent [4].IRT-4M fuel assemblies with 19.7% enrichment were developed because it was necessary to lower the fuel enrichment for research reactors [5]. These fuel assemblies are similar to the IRT-3M fuel assemblies, but their fuel elements and kernels are thicker and the gap between the fuel elements is smaller. The development work was completed in 2004. The IRT-4M fuel assemblies started to be used in VVR-SM, IRT-1, and VR-1 in Uzbekistan, Libya, and Czechoslovakia, respectively.In 1973, experiments to determine the water velocity in the gaps between fuel elements as a function of the pressure differential in IRT-2M fuel assemblies were performed at the Kurchatov Institute [6]. In 1978, similar experiments were performed for IRT-3M fuel assemblies. In the process of developing the IRT-4M fuel assemblies, comparative hydraulic calculations were performed for IRT-3M and -4M; these calculations permitted making a final choice of the IRT-4M gap and to determine the hydraulic characteristics. These experiments and calculations are described in the present article.Description of the Geometry. The IRT-2M, -3M, and -4M fuel assemblies consist of coaxial tubular fuel elements with a square cross section with rounded corners, secured on the top and bottom end pieces. Each fuel element is three-layered and consists of a kernel and cladding. The kernel is 600 mm long an...

SUBSALS: a subchannel thermal-hydraulic code for IRT type fuel analysis

“…In 1979 a new generation, the IRT-3M was developed with an enhanced heat transfer area. Finally in 2004, the IRT-4M (Figure 1) design motivated by the RERTR program was completed [1]. Currently the IRT type fuel is used in two research reactors in Czech Republic (LVR-15 and VR-1), two research reactors in Russia (IR-8 and IRT-T) and one research reactor in Uzbekistan (VVR-SM) [2].…”