UDC:

УДК 621.039.586

Abstract:

A rather complete mathematical model for calculation analysis of severe beyond-design accidents in sodium cooled fast reactorshas been developed for the first time. Unlike the current models, the model developed enables one to answer the question of the possibility of containing melted fuel in the reactor vessel. The computational domain under consideration is multiply connected. The mathematical si¬mulation of sub-domains as porous bodies was performed using mass, momentum, and energy conservationlaws, written in the form of continuity, motion, and energy equations in two-dimensional cylindrical coordinates. The problem of heat-generating layer formation on the bottom end-shield was solved. The zones of heat-generating layer were simulated. In particular, the melting of steel particles, and then those of fuel, was included by simulating the heat sinks in the heat-generating layer. The formula for heat sinks in the heat exchangers zone was derived.

The developed analytical model is implemented in the form of the BRUT computer code. Veri¬fication of individual blocks of the code showed satisfactory agreement of the calculation results with the available experimental data as well as with the results of analytical solution. A calculation analysis of a severe accident in a high power fast reactor was performed with the use of the BRUT code. The analysis considers a complete melting of fuel assemblies in the center of the reactor core and a partial melting of peripheral assemblies. Melting of assemblies results in formation of two heat-generating layers, located on the bottom end-shield of the blanket region. As the heat-generating layers heat up the bottom end-shield of the blanket region melts first with subsequent slow melting of the headers. After the headers and the pressure chamber upper plate melt-through the central heat-generating layer proceeds to the lower plate of the pressure chamber. The melt front comes to rest and heat-generating layer starts to cool off.

Using the BRUT code it was shown that in a severe accident, considered in the paper, melted fuel was contained in the reactor vessel without its destruction.

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