ICONE15-10808 Scaled Experimental Modeling of VHTR Plenum Flows

Abstract

The Very High Temperature Reactor (VHTR) is the leading candidate for the Next Generation Nuclear Power (NGNP) Project in the U.S. Various scaled heated and unheated gas and water flow facilities were investigated for modeling VHTR upper and lower plenum flows during the decay heat portion of a pressurized conduction-cooldown scenario and for modeling thermal mixing and stratification ("thermal striping") in the lower plenum during normal operation. It was concluded, based on phenomena scaling and instrumentation and other practical considerations, that a heated water flow scale model facility is preferable to a heated gas flow facility and to unheated facilities which use fluids with ranges of density to simulate the buoyancy effect of heating. For a heated water flow lower plenum model, both the Richardson numbers and Reynolds numbers may be approximately matched for conduction-cooldown natural circulation conditions. Thermal mixing during normal operation may be simulated but at lower, but still fully turbulent, Reynolds numbers than in the prototype. Natural circulation flows in the upper plenum may also be simulated in a separate heated water flow facility that uses the same plumbing as the lower plenum model. However, scaling distortions will occur due primarily to the necessity of using a reduced number of channels connected to the upper plenum than in the prototype in an otherwise geometrically scaled model.Experiments conducted in either or both facilities will meet the objectives of providing benchmark data for the validation of codes proposed for NGNP designs and safety studies, as well as providing a better understanding of the complex flow phenomena in the plenums. Power (NGNP) Project in the U.S., according to MacDonald et al., 2003. The NGNP project has the goal of demonstrating the production of emissions free electricity and hydrogen by 2015. The NGNP reactor core could be either a prismatic graphite block type core or a pebble bed core. The use of a molten-salt coolant is also being evaluated. One of the great challenges of studying, designing, and licensing the NGNP is to verify that the intended NGNP computer code analysis tools can be used with confidence to make decisions and to assure all that the reactor systems are safe and meet their performance objectives. Comparison of computer code calculations with experimental data is the key component of code verification. This paper addresses experimental modeling of lower and upper plenum flow and thermal mixing phenomena of importance during normal operation and during a loss of forced reactor cooling (pressurized conduction cooldown) scenario. A prismatic core gas-cooled reactor following the Gas Turbine-Modular Helium Reactor (GT-MHR) design from General Atomics [GA

Modeling and Simulations of Thermal-Fluid Phenomena Related to Pressurized Conduction Cooldown in High Temperature Gas Reactor

“…For safety and licensing purposes, we must analyze the transient response of high-temperature gas cooled reactors (HTGR) to hypothetical accident scenarios including Pressure Conduction Cooldown (PCC) [1][2]. The PCC is often associated with a loss of offsite electrical power resulting in failure of the blower to force coolant into the core, the reactor is scrammed and structural integrity remains intact such that there is no loss of coolant mass.…”

INL Experimental Program Roadmap for Thermal Hydraulic Code Validation

“…Similarity is more easily achieved in a steady flow and heat transfer process than in a dynamic process, such as a blowdown following a Loss of Coolant Accident (LOCA). Geometric similarity of model and prototype is often employed where three-dimensional velocity profiles are to be simulated, such as in a model of natural circulation in a pool of a fast reactor or the lower plenum flow of a VHTR (McCreery, et al, 2007). Geometric similarity has been less often employed in light-water reactor integral experiments where it is often more important to preserve pressure, including hydrostatic pressure, for component flows that are essentially one-dimensional.…”