Coupling the GUARDYAN code to subchanflow

GUARDYAN is a GPU-based dynamic Monte Carlo code developed at the Budapest University of Technology and Economics, Hungary. Dynamic Monte Carlo computes the neutron population evolution by calculating the direct time dependence of the neutron histories in multiplying systems. Some well-established Monte Carlo codes have DMC versions with coupling to Thermal-Hydraulic solvers. GUARDYAN has the computational advantage of applying GPUs, thus calculation burden can be carried by commonly available hardware, and is capable of handling power plant size systems for kinetics problems. GUARDYAN has been recently coupled to the subchannel thermal-hydraulics code SUBCHANFLOW in order to carry out dynamic calculations with TH feedback. This paper describes some convergence studies regarding reaching the initial equilibrium state. A literature-suggested set of TH input settings and high sample numbers resulted in very low statistical errors of the power estimates and stable global measures (L2) of power release, fuel, and coolant temperatures for both static and dynamic convergence. Dynamic mode low-sample simulations provided surprisingly stable global L2 measures, correct fuel temperatures, and power release, while coolant temperatures were off, without any indication of the incorrectness of the result. Static convergence showed an alternating, fluctuating L2 behavior that did not affect the final stable state.