Feasibility Assessment of a Natural-Circulation Salt Irradiation Loop in the Advanced Test Reactor

Abstract

Molten-salt reactors (MSRs) will likely require some level of irradiation testing as part of their licensing basis. An ideal experiment would consider the integrated effect of neutron flux and fission product generation in addition to circulating flow conditions. The feasibility of a natural-circulation irradiation salt loop in the Advanced Test Reactor (ATR) is assessed here. The flow is induced by the innovative combination of gas-gaps and fin-gaps along the capsule wall to finetune radial heat conductance and therefore drive an axial temperature gradient across the experiment height. Following multiple design optimizations, a promising configuration was identified. The 45-kW experiment would generate a 0.15 m/s flow velocity with 6 kg of fuel-bearing salt. This demonstrates the possibility of generating appreciable flow rates within manageable experimental conditions (e.g., total size and heat generation). An initial assessment of species mass tracking inside the experiment was also performed to gain an understanding of radionuclide behavior within the system. Results showed that significant quantities of Xe can be extracted in the off-gas (1.7 kCi) for 8% bubble removal efficiency rate. These results highlight the potential value of such experiments. Further work will involve detailed engineering drawings and analyses of the loop, as well as more computationally expensive modeling of species mass tracking.

State of Knowledge on Aerosols and Bubble Transport for Mechanistic Source Term Analysis of Molten Salt Reactors

“…A vertical orientation of the test section was found to be necessary to minimize bubble stratification for low and moderate Re numbers [41]. A natural circulation fueled-salt test loop was proposed to be built within the Advanced Test Reactor at Idaho National Laboratory (INL) to investigate radionuclide production and transport within the loop and to a connected off-gas system [121]. Such an integral effects test would shed light on bubble transport phenomena relevant to source term, especially for less-common salt mixtures such as chlorides.…”

Application of NEAMS Codes to Capture MSR Phenomena

“…This provides yet another example of the importance of multiphysics experimental investigations. A natural circulation molten salt loop of fuel-bearing salt in a neutron irradiation environment is planned and will hopefully result in irradiated corrosion experimental data [30].…”

“…Nonetheless, the impact of thermophysical properties on nearly every aspect of reactor design and safety analysis motivates research from both approaches in parallel. Additionally, recent planning for a natural circulation molten salt flow loop will aim to provide data on thermophysical property monitoring for a fuel-bearing salt in an irradiation environment [30].…”

“…Species transport modeling has many applications including modeling the impact of certain fission products on reactivity [2,37], the impact of certain salt components on redox control, and thus corrosion [22,25], and impact on source term of the transport of various phases containing radionuclides (e.g., salt, bubble, aerosol, etc.) [30,38,39], especially including the transport of tritium [24]. A brief discussion is provided below on several applications of species transport modeling and the functionalities needed for the type of simulation.…”

“…Nonetheless, validation data derived from modern experiments and measuring tools will still be needed. An example is seen by the ongoing planning for a fuelbearing molten salt loop to be irradiated in the Advanced Test Reactor (ATR) [30]. This will hopefully provide the necessary experimental data on noble metal and bubble transport and how it impacts source term assessments and other applications of fission product transport in molten salts.…”