SMR startup simulation (outdated)

Overview

In order to test and demonstrate the time dependent calculation capabilities of the Kraken framework in a reasonably realistic context, a time dependent simulation was conducted of the initial rise to power of a small modular reactor (SMR) core. The simulation used the Ants nodal neutronics code to resolve the evolution of neutronics and the xenon fission poison chain in the system and the SUBCHANFLOW thermal hydraulics code to solve the coolant flow and heat transfer in fuel rods.

The modelled SMR is the same 37 assembly Er-UO₂ fuelled core that has been previously used for the demonstration of the depletion capabilities of Kraken:

The transient starts from critical hot zero power (HZP) conditions (actually from 1 % power level) with all control rod banks at approximately 38 % insertion. The boron concentration in the coolant corresponds to the critical boron at all rods out (ARO) hot full power (HFP) conditions. The control rods are withdrawn from the core in a stepwise manner over 38 hours to allow for the accumulation of xenon in the core. To reformulate the simulation setup:

• Evaluate (in a time-independent simulation) critical boron at hot full power all rods out conditions with convergence in
  • Neutronics
  • Thermal hydraulics
  • Fuel temperature
  • Xenon
• Using that critical boron, evaluate (in a time-independent simulation) critical control rod position at 1 % power level with convergence in
  • Neutronics
  • Thermal hydraulics
  • Fuel temperature
  • Xenon
• Save initial conditions from the 1 % power level time-independent calculation.
• Start a time dependent simulation from 1 % power level and slowly withdraw the control rods fully from the core.

If the time-independent and time-dependent calculation methodologies produce equivalent steady state solutions and have been correctly implemented, the simulation should (in the end) end up in the same state as the time-independent HFP ARO calculation.