Computational investigation of the temperature and geometric characteristics of VVÉR fuel in the Kozlodui nuclear power plant (Bulgaria) under normal operating conditions

Abstract

A method of performing stationary thermomechanical calculations of VVÉR-440 and -1000 fuel elements, using the TRANSURANUS computer code to obtain the dependence of the temperature and radius of the fuel elements on the lineal power ensity and burnup, is described. These dependences are intended for use in neutron-physical calculations of the VVÉR reactor at the Kozlodui nuclear power plant in stationary and transient regimes. The results obtained with this computer program are compared with calculations performed using the certified TOPRA-s code. The comparison shows reasonable agreement between the results of calculations of the fuel temperature.Three-dimensional calculations of the core in stationary and transient regimes, performed using neutron-physical, thermohydraulic, and thermomechanical programs, based on a realistic representation and description of the state of the fuel for any moment of operation, are necessary for analyzing the physics and safety of VVÉR reactors. The real state of the fuel is determined by the instantaneous thermophysical and deformational characteristics of the fuel elements, varying as a result of complex intercoupled radiative, thermal, mechanical, and other processes. Models, computational approximations, and correlations are becoming increasingly more accurate because of the need to describe the fuel characteristics more accurately during operation in a reactor.The present paper describes a method for performing stationary thermomechanical calculations of VVÉR-440 and -1000 fuel elements using the TRANSURANUS program [1] to obtain the dependence of the temperature and radius of fuel elements on the liineal power density and fuel burnup. These dependences are used in neutron-physical calculations of VVÉR reactors at the Kozlodui nuclear power plant in stationary and transient regimes. The results obtained with this computer program are compared with calculations performed with the TOPRA-s computer program [2, 3] (certificate No. 126, April 12, 2001, from the Scientific-Technical Center of the Nuclear and Radiation Safety of the State Atomic Inspection Agency of the Russian Federation). The data from the comparison show reasonable agreement between the calculations of the fuel temperature.Determination of the Computational Characteristics of VVÉR Fuel Elements. Many parameters determine the dependences of the temperature and radius of a fuel kernel on the power and burnup: the irradiation history (time dependence

Precision Calculations of Some Neutron-Physical Characteristics of VVER-1000 Using the MCU Code

“…The feedback on fuel temperature and equilibrium concentration of xenon nuclei was taken into account separately for each fuel material. The TPA module implemented a new procedure for calculating the fuel temperature, viz., the use of a quintic polynomial approximation of the fuel temperature from the specifi c power as an alternative to the integrated quantity in the module of the certifi ed TOPRA-s code [4]. The alternative method makes it possible to calculate the fuel temperature for new fuel assembly designs, for which there are no initial data in the TOPRA-s code.…”