Validation of the Griffin application for TREAT transient modeling and simulation

•TREAT benchmark of Griffin results to experimental measurements.•Serpent Neutron transport data for a Griffin transient multiphysics model.•Comparison to 2018 transient prescription and MARCH-SETH experiments.•Improved energy deposition predictions with transient dynamic effects. The Transient Reactor Test Facility (TREAT) at Idaho National Laboratory is a graphite-moderated, air-cooled facility that was restarted in 2018 and is specifically built to conduct transient reactor tests. The Department of Energy focused modeling and simulation efforts between 2015 and 2019 on obtaining multiphysics solutions using the Griffin reactor physics application. This research has: (1) developed a consistent analysis method that automatically maps the neutronics data generated with Serpent onto the Griffin model, (2) improved the predictive capability of the traditional MCNP and Point Kinetics models that are commonly used in TREAT modeling and the preparation of engineering calculations, (3) determined the average recoverable energy in TREAT fuel per fission event, and (4) calculated a dynamic energy coupling factor that demonstrates the dependency of the energy deposition in the experiments during transients. Three experiments conducted in 2018 form the basis for the validation of Griffin for the transient modeling of TREAT. The first two experiments are 1.5% and 2.6% Δk/k transient prescription experiments with flux wires placed in the M8CAL test rig. The third experiment is a 0.6% Δk/k with the Minimal Activation Retrievable Capsule Holder (MARCH) test rig and the Separate Effect Test Holder (SETH) capsule, a light-water reactor rodlet in dry conditions. The core behavior predicted by Griffin for the transient prescription transients agrees well with the measured core power, peak power, and reactor feedback. The exception is the total energy deposition, which is underpredicted. The core behavior for the MARCH-SETH transient is significantly influenced by delayed neutrons since the reactivity insertion is delayed critical (i.e. ρ