Three-dimensional coupled kinetics/thermal- hydraulic benchmark TRIGA experiments

This research project provides separate e€ects tests in order to benchmark neutron kinetics models coupled with thermal-hydraulic (T/H) models used in best-estimate codes such as the Nuclear Regulatory Commissionʹs (NRC) RELAP and TRAC code series and industrial codes such as RETRAN. Before this research project was initiated, no adequate experimental data existed for reactivity initiated transients that could be used to assess coupled three-dimensional (3D) kinetics and 3D T/H codes which have been, or are being developed around the world. Using various Test Reactor Isotope General Atomic (TRIGA) reactor core con®gurations at the Penn State Breazeale Reactor (PSBR), it is possible to determine the level of neutronics modeling required to describe kinetics and T/H feedback interactions. This research demon- strates that the small compact PSBR TRIGA core does not necessarily behave as a point kinetics reactor, but that this TRIGA can provide actual test results for 3D kinetics code benchmark e€orts. This research focused on developing in-reactor tests that exhibited 3D neutronics e€ects coupled with 3D T/H feedback. A variety of pulses were used to evaluate the level of kinetics modeling needed for prompt temperature feedback in the fuel. Ramps and square waves were used to evaluate the detail of modeling needed for the delayed T/H feedback of the coolant. A stepped ramp was performed to evaluate and verify the derived thermal con- stants for the speci®c PSBR TRIGA core loading pattern. As part of the analytical benchmark research, the STAR 3D kinetics code (Weader, 1992, STAR: Space and time analysis of reac- tors, Version 5, Level 3, Users Guide, Yankee Atomic Electric Company, YEAC 1758, Bolton, MA) was used to model the transient experiments. The STAR models were coupled with the one-dimensional (1D) WIGL and LRA and 3D COBRA (Rowe, 1973, COBRA IIIC: A digital computer program for steady-state and transient thermal-hydraulic analysis of rod bundle nuclear fuel elements, Battelle Institute, Richland, WA). T/H models to determine the level of T/H modeling required to accurately describe the behaviour of the PSBR TRIGA core during these transient conditions. STARʹs 1D T/H models (WIGL and LRA) were adequate for the rapid pulse events, when accurate temperature-dependent fuel thermal constants were used and the reactor coolant feedback mechanism was small. However, the longer transients (i.e. ramps, square waves) necessitated the use of the COBRA 3D ¯uid ¯ow analysis coupled with the 3D STAR kinetics model.