Background Passive Containment Cooling Systems (PCCSs), which cool down a reactor containment vessel during a loss-of-coolant accident, are important safety elements in nuclear power plants. Previous studies have shown significant degradation of steam condensation heat transfer in the presence of non-condensable gases like air. The performance of PCCS devices under such conditions is important to benchmark NRC safety codes. Methods The single-phase asymmetric water flow inside a generic model of a thermosiphon PCCS was modeled using COMSOL Multiphysics, comparing 3D and 2D axisymmetric model geometries, steam condensation approximations, and buoyancy effects. Results Mesh refinement effects appeared more significant for result accuracy than 3D effects. Variable and constant heat transfer coefficient boundary conditions produced nearly constant heat flux along the surface of the pipe. Examining the impact of buoyancy effects shows that the PCCS system is operating at the point where buoyancy’s impact is heavily dependent on the system flow rate. Conclusion The significance of these results for analyzing data from the OECD/NEA-sponsored PANDA test series is discussed. The constant heat flux approximation appears accurate for future modeling.
The United States leads the world in small modular reactor (SMR) designs and has yet to complete a commercial deployment. Federal awards, hyperscaler agreements, and state funds are now underwriting first units for the leading projects, but serial factory production, the basis of the SMR value proposition, has begun nowhere, because the supply chain has neither a standard to tool against nor firm orders that justify tooling. This article asks what the minimal sufficient intervention is. Comparative analysis of SEMATECH, the French and Korean nuclear programs, and five decades of American standardization and cost-share attempts yields four diagnostic dimensions, and seven candidate instruments are rated against them on a five-point scale. None is sufficient alone. The design that prevails pairs two institutions for light-water SMRs and dominates a SEMATECH-style broad-membership consortium. In consensus standards work, ASME code cases carry vessel and component design rules, an ASTM International subcommittee writes the material, fabrication, and test specifications those rules cite, and the NRC accepts the result through its existing incorporation-by-reference process. A time-limited program in the DOE Office of Nuclear Energy, holding a no-year appropriation, makes fixed milestone payments and commits to buy the unsubscribed share of each qualifying unit’s output, up to a cap, so any design meeting the specifications competes and the purchase commitment pays only where private subscription falls short. The standards make federal demand vendor-neutral, and federal demand makes the standards bankable; neither works alone. The authority sunsets at seven years while obligated contracts remain in force. Coordination is necessary but not sufficient: the framework exists to run the serial-production cost test, not to guarantee its result.
Liquid-fueled molten salt reactors present a complicated modeling problem due to the spatial distribution of radionuclides throughout the system. The mechanisms of transfer for species in the system vary widely depending on the location in the reactor. To accurately model the inventory in an off-gas system, all transfers throughout the system must be considered. In this document, following an introduction to fission products, a review of considerations for this modeling problem is presented. Modeling considerations are detailed, including discussion of the thermophysical properties such as volatility and solubility of species in molten salt. Mass transfer theory and applicable scenarios in molten salt, graphite, and helium bubbles is discussed following this. An extensive list of mass transfer correlations that may be applicable in molten salt reactor systems with explanations provided for each is also provided. The ability to detect species in an off-gas system is also discussed based on historical data. Lastly, a general framework for the numerical solution of the system is suggested along with future steps towards implementation of the methodology discussed.
Liquid-fueled molten salt reactors present a complicated modeling problem due to the spatial distribution of radionuclides throughout the system. The mechanisms of transfer for species in the system vary widely depending on the location in the reactor. To accurately model the inventory in an off-gas system, all transfers throughout the system must be considered. In this document, following an introduction to fission products, a review of considerations for this modeling problem is presented. Modeling considerations are detailed, including discussion of the thermophysical properties such as volatility and solubility of species in molten salt. Mass transfer theory and applicable scenarios in molten salt, graphite, and helium bubbles is discussed following this. An extensive list of mass transfer correlations that may be applicable in molten salt reactor systems with explanations provided for each is also provided. The ability to detect species in an off-gas system is also discussed based on historical data. Lastly, a general framework for the numerical solution of the system is suggested along with future steps towards implementation of the methodology discussed.
Some 43 years have passed since federal legislation established 1998 as the year for the United States Department of Energy (DOE) to begin taking title and possession of used nuclear fuel from commercial nuclear power plants including the now-retired San Onofre Nuclear Generating Station (SONGS). Southern California Edison (SCE) is decommissioning the retired nuclear plant but cannot restore the land until the used fuel is relocated offsite. While used fuel is safely stored at San Onofre, the material eventually must be permanently isolated from the biosphere in a deep geologic repository. Nuclear utility customers who pre-paid billions of dollars for disposal deserve solutions. Although SCE cannot control outcomes, it is catalyzing action. In 2021, SCE published the Strategic Plan for the Relocation of SONGS Spent Nuclear Fuel to an Offsite Storage Facility or a Repository. 1 At that time, SCE partnered with local governments to form Spent Fuel Solutions 2 —an advocacy coalition that has grown to more than 300 members from 18 states. SCE and Spent Fuel Solutions are working to amend federal legislation and establish a more durable used fuel program that includes near-term storage and long-term disposal. Efforts include raising awareness about the issue and supporting DOE initiatives to collaborate with potential host communities for used fuel facilities. The used fuel challenge is an old one, dating to 1982 when the Nuclear Waste Policy Act (NWPA) of 1982 3 was enacted. Legislative reform is difficult, but the current push for energy abundance is bringing renewed attention to the role of commercial nuclear power. The lack of solutions to the back end of the fuel cycle risks impeding the deployment of advanced reactors in the US. SCE is working to navigate a window of opportunity that may finally make away-from-reactor storage and disposal facilities a reality.
