Kascheev M.V., Sorokin A.P.
A.I. Leypunsky Institute for Physics and Power Engineering, Obninsk, Russia
A mathematical model has been developed for the first time for numerical analysis of severe off-design accidents in sodium cooled fast reactors. Unlike the presently existing models, the developed model enables one to answer the question of the possibility of containment of molten fuel in the reactor vessel.
The computational domain under consideration is multiply connected. The mathematical simulation of sub-domains as porous bodies is performed using the laws of conservation of mass, momentum, and energy, written in the form of equations of continuity, motion, and energy in two-dimensional cylindrical coordinates. The problem of formation of heat-generated layer on the lower end shield has been solved. The zones of heat-generated layer were simulated. There was obtained solution of the problem on the movement of variable mass vapor bubble in liquid. The results have been used to describe the heat sources originated due to vapor condensation above heat-generated layer.
The developed mathematical model is implemented in the form of BRUT computer code. Verification of the code’s individual blocks has revealed an adequate agreement of the calculation results and available experimental data as well as analytical solutions. Using BRUT code there was performed calculation analysis of UTOP accident at BN-type high-power reactor with nitride fuel and MOX-fuel. In all versions melt was contained in the reactor vessel.
To effectuate fast evaluations of parameters and, foremost, time of melt-through of designs there was developed mathematical model in which the task is solved in one-dimensional approach. By the BRUT-O code, developed on the basis of one-dimensional mathematical model, calculation of accident wherein occurs complete melting of fuel subassemblies in the center of the reactor core and partial melting of peripheral fuel subassemblies is carried out. It is shown that time for melt contact with the pressure-header upper plate calculated by the BRUT-O code is less than the similar time obtained by the BRUT code to 10%.
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