The MCU-PTR program with a MDBPTR50 database has been developed. The purpose of this program is to perform high-precision mathematical modeling of nuclear reactors and to calculate their neutronphysical characteristics. The program uses the Monte-Carlo method to solve the equations governing n, γ radiation transfer and uses evaluated data describing the interaction of neutrons and photons with matter. The change of the isotopic composition of the reactor materials during the operation of the reactor is taken into account. The organization of the program makes it possible to organize parallel computation and perform the calculations on super and personal computers with multinuclear processes. The dynamical distribution of the memory removes the restrictions on the mathematic models of the reactor. The program is intended for computational tracking of the operation of research reactors, validating upgraded designs of reactors, planning, and optimizing experimental conditions with respect to nuclear physics, radiation materials science, creating optimal conditions for producing radionuclides, and solving nuclear and radiological safety questions for operating and shutting down reactors.The MCU project started at the Russian Science Center Kurchatov Institute in 1982. The problem was to develop high-precision reactor programs which rely on evaluated data on the interaction of radiation with matter and using the Monte Carlo method to solve the transport equations governing the transfer of neutrons and other forms of radiation. Over this period of time the family of MCU programs was developed and put into operation [1].The work on the MCU-4 package was completed in 2004 [1]. Several working programs certified by Rostekhnadzor for various applications were built from MCU-4 modules. The programs MCU-RR and MCU-RR/P were developed for the research reactors at the Scientific-Research Institute of Nuclear Reactors [2, 3].The last version MCU-5 differs radically from its predecessors: it permits organizing a parallel calculation at all stages of the operation of the program and performing the calculations on super and personal computers with multinuclear processors. This gives a real possibility of performing massive high-precision calculations of full-scale models of reactors. The dynamical distribution of memory optimizes the use of the computer's operational memory and makes it possible to expand substantially the parameters of the mathematical model.The physical, geometric, and transport modules in MCU-5 are a modification of the MCU-4 modules. The detection module is written from scratch. The burnup module is reworked considerably and the constants base is updated.The modules in the MCU-5 package have been used to develop the MCU-PTR program with the MDBPTR50 database. Its purpose is to perform calculations of the effective neutron multiplication coefficients k eff , the spatial-energy dis-UDC 621.039.5.
The objective of this conference was to exchange information and prepare further collaboration concerning the program of lowering the fuel enrichment of research and tests reactors.In 1994, a program for developing fuel elements and fuel assemblies for research reactors using fuel with 20% 235 U enrichment was initiated, which is part of the US program on lowering fuel enrichment used in research reactors. The Russian part of the program included the continuation of the development of fuel elements and assemblies for VVR-M2, IRT-3M, and MR with uranium dioxide fuel, development of high-density fuel, as well as fuel elements and assemblies of VVR-M5, IRT-3M, and IVV-10 reactors with such fuel [1].Development of IRT-4M Type Fuel Elements and Assemblies with Uranium Dioxide Fuel Enriched with 235 U to 19.7%. When decreasing the fuel enrichment to 19.7%, the 235 U content must be increased as compared with 36% enrichment fuel. To this end, in 1994 the Kurchatov Institute started the development of IRT-4M fuel assemblies, which are similar to IRT-3M assemblies, in which the widths of the fuel assemblies were increased from 1.4 to 1.6 mm, and the widths of the gaps between them were decreased from 2.05 to 1.85 mm, respectively. For this gap width, the water velocity in them will decrease by no more than 5%. The kernel thickness was increased from 0.4 to 0.7 mm, and the nominal cladding thickness is 0.45 mm, which is adequate for maintaining seal tightness [2]. For 400 g 235 U content in the eight-tube IRT-4M fuel assembly, the uranium content in the kernel is 3.85 g/cm 3 (Fig. 1).In May 1996, testing of individual size-types of fuel elements, perfected by the Novosibirsk Chemical Concentrates Works, as part of an experimental fuel assembly (Table 1) began in IR-8 without waiting for the technology for fuel elements of all sizes for IRT-4M fuel assemblies to be perfected. The tests were performed under the following conditions:
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...
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