From left to right: Reflooding facility, STERN lab. In Hamilton (Canada) and COAL test device. Photo: IRSN, France

International Standard Problem (ISP) based on the IRSN reflooding COAL experiments

The IRSN COAL reflooding experiments are based on four 7x7 full-length electrically heated rod bundles. Since 2020, over 75 experiments have been conducted under large and intermediate break LOCA reflooding conditions. The fuel rods correspond to a 17x17 PWR design. Fuel bundle B0 is undeformed, whereas B1, B2, and B3 bundles have 4x4 fuel rods region with clad ballooning and local overpower to simulate the effects of fuel fragmentation and relocation at their middle elevation. The fuel rod geometry as well as the axial power profile remains unchanged during the experiments.

From left to right: Bundle Bo and Bundles B1 to 3. Photo: IRSN, France

The aim of the proposed CAPS is to carry out an International Standard Problem that involves four LOCA reflooding tests conducted using the IRSN COAL device to:

• Perform code-to-experiment comparison between thermal hydraulic computer codes and the COAL reflooding experimental results,
• Assessing the predictability of computer codes in the context of reflooding both intact and ballooned fuel rods requires consideration of the impact of fuel fragmentation and relocation on local overpower conditions.

In line with the goals of the ISP, four reflooding LOCA tests have been chosen:

• Two taken from the B0 undeformed fuel bundle series:
  B0-03-50 performed at a pressure of 3 bar and 50 kg m^-2s^-1 reflooding rate and B0-20-17 performed at 20 bar and 17 kg m^-2 s^-1 reflooding rate

• Two taken from the 90% deformed B2 fuel bundle series:
  B2-03-50 performed at a pressure of 3 bar at 50 kg m^-2s^-1 reflooding rate and B2-20-17 performed at 20 bar and 17 kg m^-2 s^-1 reflooding rate.

The initial phase of the ISP will involve simulating the two B0 undeformed COAL experiments. Comprehensive details on the experiment, including geometry, boundary conditions, and experimental outcomes, will be supplied, making it an "open benchmark."

Concurrently, the second phase of the ISP will involve simulating the two B2 deformed COAL experiments. All details of the experiment, including geometry and boundary conditions, will be supplied, excluding the experimental outcomes. Thus, it will serve as a "blind benchmark."

The third phase of the ISP will involve simulations of the two B2 deformed COAL experiments, incorporating the provided experimental results ("open benchmark").

An uncertainty propagation exercise will be conducted in each phase.