A. A. Tutnov

Pulsar-2: Mathematical modeling of thermophysical and thermomechanical processes in the fuel elements

A method for modeling thermophysical, strength, and reliability characteristics of fuel elements during quasistationary, transitional, and maneuvering reactor operating modes is described. Calculations were performed on a full-scale model of a cylindrical fuel element from a power reactor. Processes described mathematically included thermoelastic expansion of fuel and cladding; creep of fuel and cladding; plastic deformation of cladding when the fuel element reaches nominal power and during maneuvering of the power; swelling of the fuel; radiation-induced additional sintering of fuel pellets; radiation growth of the cladding; release of gaseous and volatile fission products under the fuel element cladding; cracking and fragmentation of UO{sub 2} pellets; restructuring of the fuel molecular, contact, and radiation conductivity of the gas gap; mechanical interaction of the fuel column with the cladding damage and cracking resistance of cladding material under conditions of corrosion under stress; and heat emission at the fuel element outer surface. The empirical PULSAR-2 code, which incorporates three models of fuel-cladding mechanical interactions, was used to calculate the deformation of fuel due to swelling. Results of mathematical modeling are summarized and compared with experiment results for BBER-440 fuel elements; computational results are in good agreement with experimental data. 14 refs., 7 figs.

A calculated basis for the strength and failureprobability of VVÉR contaiment

Basic features are presented on the calculation method for determining the strength and failure probability of a VVÉR containment vessel. A description is given of the computational method, which handles five related tasks: simulating the coolant convection in an accident involving the cooling water in the body of the reactor; calculating the nonstationary temperature patterns in the body; simulating the state of stress and strain in it; calculating the cracking resistance (brittle strength); and quantitative probabilistic analysis of containment failure hazard.

Verification of PULSAR+software

Experiments on shell oxidation in fuel-element simulators have been conducted at several organizations: the Kurchatovskii Institute Russian Scientific Center (RSC) [3], the A. A. Bochvar All-Russian Scientific-Research Institute of Nuclear Materials (ASINMi [4], and the All-Russian Institute of Atomic Materials (AIAM). Very different experimental techniques were used. For example, at the Kurchatovskii Institute RSC, the samples were heated by electric-current transmission, The apparatus permitted the creation of both internal and external pressure for the simulator of fuel-element shells for VVI~R and RBMK reactors. At ASINM, the oxidation of short samples of VVI~R shell tubes was studied on equipment with indirect heating in a flow of hot steam, and no pressure difference was applied to the samples. In the present work, verification is based solely on experimental data from the Kurchatovskii Institute RSC and AIAM. Comparison shows that results calculated on the basis of the mathematical model developed at the Kurchatovskii Institute RSC are in good agreement with the experimental data (Table 1).