Numerical simulation of the open-pool reactor coolant system using a multi-domain approach

Abstract

The computational simulation of large-scale reactors is currently limited by the high computational cost. The system codes allow addressing these problems, although with the well-known loss of local information. The use of coupling domains to reduce the problems looks like a proper alternative to settle this issue. In the present paper, a multi-domain coupling 3-dimensional/0-dimensional method to solve the thermal hydraulics of the TRIGA Mark I IPR-R1 reactor was implemented into a Finite Volume suite. Despite of the broadly literature about coupling methods, even in the nuclear engineering community, most of them manage with different codes in a fully explicit way. In the other hand, the benefit of solve different domain approaches inside the same software is in the use of monolithic algorithms. The proposed method consists on using 3-dimensional full CFD to simulate the reactor pool and 0-dimensional modelling for the external cooling loop. This is made by implementing a set of ad hoc dynamics boundary conditions to model the momentum and energy balances along the pipeline. This strategy was used to perform long-time steady state simulations of the reactor at the design power of 100 kW as well as for the repowering up to 265 kW. The results demonstrated that the core is efficiently cooled at the higher power without need to increase the coolant mass flow rate of the external system. Moreover, two accidental events were simulated: the first case was the Station Black Out at full power of 265 kW. The results indicated that the loss of the external heat sink led to a slow pool heating, but the core remains being cooled by the natural circulation in the pool. In fact, the mass flow rate through the core is only reduced in 15% by the loss of the external loop circulation. Finally, a large-Loss of Coolant Accident for the operational power of 100 kW and keeping the pump running is performed. In this case, the pool is quickly empty if safety systems do not take action and the core is uncovered after 450 s completely losing the core cooling capacity.