Comparison of experimental data and PULSAR-2 calculations for different fuel assemblies and reactors

Abstract

The PULSAR-2 code is intended for modeling the behavior of thermophysical, strength, and deformation characteristics of fuel elements of power reactors operating in quasistationary, transient, and maneuvering modes [1]. In 1996 the code became the first mechanical-thermophysical code, certified at the Georgian Academy of Sciences of the Russian Federation, for modeling fuel elements of power reactors. The present paper presents examples of verification of the code on experimental data.Comparison of Modeling Results with Experimental Data for Fuel Elements of the 13624637 Fuel Assembly Which Operated for Three Fuel Runs in the VVER-440 Reactor at the Lovis-2 Nuclear Power Plant (Finland). Fuel assemblies with this factory number were removed from the reactor in 1991 for comprehensive inspection [2]. It contained 12 well-inspected fuel elements arranged along the periphery of the assembly. Pelleted fuel with density 10.55-10.63 g/cm 3 was used in the fuel elements. The pellets had beveled edges and central openings. The fuel assembly reached an average burnup of 43.7 MW.days/kg. The maximum linear thermal power averaged over the assembly was reached at the beginning of the first year of irradiation and equaled 192 W/cm.Six fuel elements were subjected to post-reactor investigations and computational analysis. Their characteristics corresponded to VVI~R-440 standards; the initial helium pressure beneath the jacket equaled 0.63 MPa. The fuel pellets possessed a 1.4 mm in diameter opening at the center. The enrichment equaled 3.6%. The fuel elements were 2530 mm long, including a 90-ram compensator. Post-reactor investigations included data on the vertical distribution of the residual changes in the jacket diameter, the residual elongation of the elements, and the change in structure of the fuel pellets. Investigations showed that the fuel in the fuel elements broke up into fragments in a region located at the vertical center. The calculations showed a similar picture. Experimental investigations did not show any changes in the fuel microstructure. Therefore the temperature did not exceed 1500"C. Modeling gave the same result (Fig. 1). Figure 2 shows good agreement between the experimental and computed distributions of the change in diameter over the height of the fuel element. Modeling showed that the residual elongation of the fuel elements (creep + radiation growth) fluctuates in the range 6.5-9 mm; the experimental elongation is 7-9 ram.Comparison of Modeling Results with Experimental Data for Fuel Elements of the 13624638 Fuel Assembly Which Completed Four Runs in the V'VI~R-440 Reactor of the Lovis-2 Nuclear Power Plant. The fuel assembly was removed from the reactor in 1992 [3]. The fuel elements of this fuel assembly differed from those of the preceding assembly by the thermal power history and burnup. The general characteristics of the fuel elements of both fuel assemblies are the same. The maximum linear thermal power, averaged over the fuel assembly, was reached during the second year of irradiation and equ...