Coupled system dynamics and computational fluid dynamics simulation of plant transients in sodium cooled fast reactors

Highlights: • Traditionally plant dynamics codes adopt one dimensional modeling for entire plant. • This approach fail to address stratification effects in hot pool of fast reactor. • A hybrid combining CFD based model along with system dynamics is presented. - Abstract: Analysis of transient thermal hydraulic behavior of the plant during various design basis events is important for (i) demonstrating safety, (ii) design of plant protection system, (iii) deciding safety parameters, (iv) design specification on response time of systems and instruments, (v) estimation of transient thermal loading on various structures and (vi) meticulous planning of plant operating strategy. Traditionally these studies are carried out using one-dimensional system dynamics models. Due to the presence of large sodium pools in the primary circuit of prototype fast reactors, there is a possibility of significant stratification effects which may govern the transient under certain plant conditions. Traditionally, sodium pools are treated as single well mixed volumes or network of one dimensional control volumes in system dynamics models. One-dimensional models fail to simulate stratification effects leading to unrealistic transient simulation. An integrated code system with coupling of one dimensional and multi-dimensional models is an optimum approach to overcome this difficulty. This paper discusses development of multi-dimensional transient CFD code for turbulent flow simulations in stratified sodium pool of a fast reactor and integration of the same with one dimensional system dynamics models for the rest of the plant. The predictions of the improved code are compared against those of system dynamics model of entire plant.