Four-Phase C5G7 Transient Benchmark for Neutron Transport

Problem description

A multi-group small PWR-type reactor featuring four different transient phases driven by time-dependent source and continuous movements of control rods.

The geometry model and material cross-sections are based on the C5G7-TD benchmark [link]. A neutron source, uniformly distributed in the center pin cell of Assembly 4 (South-East), isotropically emits neutrons of the highest-speed energy group within the time t = 0 to t = 15 s. The problem features continuously moving control rods and is simulated up to t = 20 s.

The assembly-wise movements of the control rods (CRs) are shown in the file control-rod-position.png. The time-dependent source and the movements of the control rods result in the four transient phases:

• Phase 1 (0 to 5 seconds): source-driven deeply subcritical system, reaching a steady state;
• Phase 2 (5 to 10 seconds): gradual withdrawal of CRs, manifesting the S-shaped curve of reactivity worth in the total fission rate evolution;
• Phase 3 (10 to 15 seconds): reactivity excursion, exhibiting rapid population growth;
• Phase 4 (15 to 20 seconds): shutdown, followed by significant delayed neutron effects.

The quantity of interest is the 4D fission rate distribution binned into pitch-sized uniform spatial mesh (1.26 cm x 1.26 cm x 1.26 cm) in the core active region and 0.1 s uniform time mesh, resulting in 200 x (17x2) x (17x2) x (17x6) mesh bins.

Data provided

• build-xml.py: OpenMC XML input builder script
• output_*.h5: OpenMC Statepoint results run with increasing numbers of source particles per batch (over 30 batches)
• MGXS-C5G7.h5: Multigroup cross-section data of the C5G7-TD model
• control-rod-position.png: positions of the four control rod banks in time
• mean.gif and sdev.gif: Visualizations of the quantity of interest from output_4.h5 data
• difference.gif: Relative difference between MC/DC and OpenMC results
• convergence.png: Convergence of the 2-norm of the relative difference between MC/DC and OpenMC results

The OpenMC results were generated using the following release.