Conference Agenda

Direct Air Capture (DAC) is a technology that separates and captures CO₂ contained in trace amounts in the atmosphere. It is the only existing CO₂ capture process with a negative net emission and is receiving attention as an active CO₂ removal technology (Carbon Dioxide Removal (CDR)) to achieve net zero. Currently, DAC has low technological maturity overall, and the large amount of air intake requirement and the large amount of heat energy consumption for regeneration are pointed out as major bottlenecks in technology commercialization. Linking with nuclear power, a carbon-free power/heat energy source, is one of the effective strategies to resolve the technological bottleneck of DAC, but the research and development for this is still in the basic development stage. In this paper, at first, it is explored the concept development research of the nuclear power-DAC combined system currently in progress and evaluate the development level. In addition, it will review the technical feasibility of the DAC system, development of the system, the current level of technological development, and propose technology candidates for linking with nuclear power.

In the Republic of Korea, the development of the innovative Small Modular Reactor (i-SMR) is ongoing. The i-SMR will be equipped with the following three passive safety systems to replace the active safety systems of existing commercial nuclear power plants: Passive Emergency Core Cooling System (PECCS), Passive Auxiliary Feedwater System (PAFS), and Passive Containment Cooling System (PCCS). The PECCS performs the core makeup/cooling function, the PAFS removes residual heat with theby steam generator (SG) cooling, and the PCCS conducts the heat removal from the containment vessel (CV) atmosphere. Since the passive safety system can carry out safety functions by natural forces without continuous power supply or any operator action, it is expected to dramatically improve the safety of nuclear power plants (NPP). In this paper, we present the design status of the passive safety systems in the i-SMR and the performance analysis results using MARS-KS.

This paper extends the evaluation of an adaptive algorithm for estimating decay heat in transient scenarios with steadily decreasing reactor power. The previously introduced approach offers a low-cost alternative with simpler implementation to traditional methods that typically rely on extensive nuclide tracking or standardized procedures. The adaptive algorithm utilizes precomputed decay heat curves from SCRAM scenarios, and enables real-time decay heat estimation during simulation while dynamically adjusting to varying power levels without requiring detailed nuclide tracking.
This study applies the adaptive algorithm to additional non-SCRAM shutdown scenarios in a sodium-cooled fast reactor, demonstrating its flexibility in handling diverse transient conditions. Verification is performed by comparing results with Monte Carlo depletion calculations using Serpent, confirming high accuracy. Furthermore, the model is successfully applied to FFTF LOFWOS Test #13, showing good agreement with experimental decay heat data. These results demonstrate the potential of the adaptive method as an accurate decay heat estimation approach for real-time transient simulations of advanced reactors.

The water-based Natural convection Shutdown heat removal Test Facility (NSTF) at Argonne National Laboratory is a large-scale test facility built to study passive decay heat removal performance of one Reactor Cavity Cooling System (RCCS) concept for advanced nuclear reactors. The inventory fill within the primary water tank is known to have an impact on the natural circulation thermal hydraulics and two-phase phenomena development, including instabilities such as startup oscillations. Six inventory levels, from 20% to 80% initial fill, were examined. The facility was heated from room temperature to an input power corresponding to 2.1 MW_t full-scale (51.6 kW_t NSTF-scale) and operated at saturation conditions for at least four hours, uninterrupted. While minor changes to integral thermal hydraulic characteristics and instabilities were observed, ultimate heat removal performance was not impacted by decreasing inventory. Following the last 20% fill test, a depletion scenario was performed where the facility continued operating at saturation conditions with boil-off until reaching critical levels where natural circulation flow stagnated. Comparisons were made to similar, previous inventory parametric series and depletion tests. The height of the tank inlet has an impact on the development and suppression of the natural circulation instabilities as well as natural circulation stagnation conditions. However, the lower tank inlet resulted in significant increase in available inventory prior to stagnation in a boiloff scenario. Additionally, no short-circuiting effects between the hot and cold legs were observed as a result of the lower tank inlet.

The objective of the present study is to investigate the effects of varying decay heat loads and tank inlet elevation on the performance of a large-scale water-based Reactor Cavity Cooling System (RCCS). The water-based Natural convection Shutdown heat removal Test Facility (NSTF) at Argonne represents a ½ axial scale and 12.5° sector slice of the full-scale Framatome 625 MWt SC-HTGR RCCS concept. A power parametric series with prototypic decay heat loads of 1.4, 1.75, 2.1, and 2.4 MWt (34.4, 43.0, 51.6, and 58.5 kWt scaled) with the lower tank inlet configuration was first discussed. System performance metrics at the two-phase quasi-steady state were compared, mainly the system flow, steam generation rate, system pressure, and liquid and structure temperatures. The effect of the decay heat power level on the boiling front progression was also investigated. It was found that lower decay heat loads would cause delayed boiling front progression. Results were then compared to previous data sets collected at identical testing condition but with chimney pipnig configured at the mid tank elevation configuration. Overall, the tank inlet elevation did not significantly influence the system two-phase quasi-steady-state performance at the studied decay heat levels. However, the tank inlet elevation was found to have significant impacts on the two-phase flow instability characteristics and the boiling front propagation. At the lowest power of 1.4 MWt with the lower tank inlet configuration, boiling never propagated from the tank to the upper chimney, while boiling propagation to the upper chimney was observed in the mid tank inlet configuration.