Comparative Study of Cold Ramp Tests Simulations with the Thermo-Mechanical Code TESPA-ROD and the Subchannel Code CTF

Abstract

The OECD/NEA published the Multi-physics Pellet Cladding Mechanical Interaction Validation (MPCMIV) Benchmark (here Rev. 3 of the specifications). This benchmark is based on experimental data from the R2 research reactor in which nearly 150 ramp tests were specifically designed for PCI/PCMI problems. While the benchmark is aimed mainly at the validation of multi-physics phenomena, the so-called “Tier 4” exercises focus on the validation of traditional fuel performance codes, using boundary conditions from measurements, namely the coolant pressure, mass-flow and inlet temperature, and the axial linear heat rate.

The CTF code is an advanced version of the well-known subchannel code COBRA-TF, co-developed at the North Carolina State University (NCSU) and Oak Ridge National Laboratory (ORNL). In the last decade the fuel model in the thermal-hydraulics subchannel code COBRA-TF has been further developed and improved. However, it remains a simplified model compared the ones found in dedicated codes. The TESPA-ROD code analyses the thermo-mechanical behavior of the fuel rod for RIA-transients, LOCA-transients, PCMI-transients, and interim storage. The fuel rod is represented in a 1½ dimensional spatial resolution.

The first and second cold ramp tests of the Benchmark are simulated with both codes and their results compared. The parameters of interest are the fuel rodlet gap width, the centerline temperature, and the radial temperature distribution. The comparison allows to identify differences in the models and correlation used in the rod models of CTF and TESPA-ROD.

This work is the first step toward a tri-code multi-physics coupling between neutronics, thermal-hydraulics and thermo-mechanics. The next step will be the offline coupling between CTF and TESPA-ROD.