Conference Agenda

In molten salt reactor (MSR) systems, tritium is generated in significantly larger quantities when compared to other reactors. Due to tritium’s high permeability and solubility, tritium must be removed from the molten salts to reduce the associated radiological risk. Gas sparging is used for the online separation and removal of fission products within FLiBe where noble gas is bubbled through the molten salt to remove dissolvable fission gasses. To advance gas sparging technology, we are doing experiments to develop a detailed understanding of gas sparging behavior and create benchmark datasets for Multiphysics Object Oriented Simulation Environment (MOOSE) models. To do this, we have designed and built the Modular Separate Effects Test Facility (MSEFT) - Tritium Removal Investigation of Transport Interactions Using Mass-transfer (TRITIUM) flow loop to observe and measure localized bubbling behavior and integral gas concentrations using surrogate fluids. The Normalized Dissolved Oxygen Concentration (NDOC) within the surrogate fluid will be reported on for different prototypical conditions. The NDOC is used to characterize the liquid-gas mass transfer coefficients of sparging bubbles within water at various glycerol weight percentages used to match relevant non-dimensional numbers of Reynolds, Sherwood, and Weber. The NDOC data will be combined with measurements of relevant local bubble dynamics including average bubble diameter and velocimetry taken with high-speed shadowgraphy and Particle Image Velocity systems. These combined measurements will be useful to inform future design improvements for different MSRs’ gas sparging components.

In prior studies, we introduced an optimized prototypical natural circulation water-based reactor cavity cooling system (RCCS) design for a pebble-bed generic FHR based on 1D modeling and in later work performed more detailed 2D transient performance analyses. The prototypical design was an initial step to facilitate experimentation. Experiments in a university laboratory necessitate downscaling of the prototypical RCCS while maintaining key non-dimensional parameters such as Grashof number, particularly in systems involving natural circulation. The design of the RCCS, core, and the radiated power significantly affect the non-dimensional parameters in the RCCS. Tradeoffs exist between the non-dimensional parameters as a combination of design parameters may yield ideal scaling for one parameter but result in unacceptable scaling for other parameters. In this work, we systematically study the dependence of the relative scaling of the non-dimensional parameters compared to the prototypical case as a function of design and physics parameters using an iteratively refined base case design. These non-dimensional parameters considered herein include Grashof, Reynolds, Nusselt, Prandtl, Rayleigh, Biot, Stanton, Froude, and Richardson numbers. An idealized, downscaled design was obtained based on these analyses and a practical experimental setup was subsequently designed.

Kairos Power recently obtained NRC approval for construction of its high-temperature fluoride-salt cooled pebble bed reactor, Hermes, and is presently working towards submission of its operating license. As part of this activity, Kairos is using the KP-SAM systems code to perform safety analysis of the reactor under transient conditions. As part of the verification & validation (V&V) of this code, Kairos has built and operated a reduced-scale integral effects test (IET) facility which leverages hierarchical two-tiered scaling (H2TS) to simulate a loss of forced circulation (LOFC) in the reactor in which a pump failure leads to the onset of natural circulation. This facility employs a surrogate heat transfer fluid which simultaneously matches several dimensionless numbers – such as the Prandtl number – of molten salt at a significantly reduced temperature and scale, enabling rapid testing with high-fidelity instrumentation. This paper discusses the scaling, testing campaign, results, and future plans for the IET.

We present selected integral effect test results conducted in the STELLA 2 facility on the decay heat removal systems (DHRS), along with numerical analyses with MARS LMR system thermal hydraulics code. STELLA 2 is a large scale sodium test platform modeled after the Korean sodium cooled fast reactor, PGSFR, with a 1/5 scale reduction in length. The facility aims to evaluate the overall plant dynamics and safety aspects of the reactor under long term transient conditions. With equivalent conservation of the reactor components’ shapes and layouts, reactor transients can be investigated while maintaining the integral behavior and interactions of the prototypic reactor’s heat transport systems with minimal distortions. The facility has four individual DHRS loops, comprising two active and two passive loops differentiated by their cooling mechanisms for ultimate heat sinks. The selected tests focus on scenarios where the primary system after reactor shutdown relies solely on two DHRS loops, postulating a loss of offsite power condition. Overall, the system code successfully captured the general transient behaviors in the individual loops, although variations were observed in the peak temperature and the time to reach it, compared to the experimental data. It is believed that discrepancies in local temperature distributions, particularly in larger volumes, are attributed to the system code’s limitations in discretization method and relations.