By Dr. Nick Touran, Ph.D., P.E., 2023-04-16 , Reading time: 6 minutes
The term advanced in nuclear is used loosely to mean “reactors that are better than ones you’re worried about”. Due to the fact that a huge number of somewhat exotic reactor types were built and tested in the 1950s and 1960s, the term is somewhat misleading and complex. Depending on who you talk to, advanced reactors can mean a number of quite different things:
These advanced reactors have incorporated real-world, experience-informed lessons learned from previous versions of any given reactor make into newer, better, more optimized models. They generally have been built before, have existing supply chains, have licenses from the regulators, and are sitting around ready for people to purchase them. Examples:
These advanced reactors have characteristics designed to enhance the performance beyond the (already stellar) capabilities of the workhorse reactor fleet of light-water reactors (LWRs). Such advancements may include:
Related to definition 2, in 2000, experts in the international nuclear power community came together in the Generation-IV International Forum (GIF) to help guide the industry’s path forward. Over 100 experts looked through 130 reactor types proposed and chose the 6 most promising reactor types that they agreed had high potential to reach higher performance in 8 specific technology goals, listed here.
The discussion around nuclear reactors types has struggled since the early 1950s to differentiate between the purported benefits of conceptual reactors and the actual performance of built-and-operating real reactors. Admiral Rickover most famously summarized the situation in his paper reactors vs. practical reactors memo, which sharply criticized people who promoted the hypothetical benefits of reactors that were not yet built over reactor projects that were in construction or operation.
In many senses, advanced reactors as used in modern discussions are basically identical to the academic reactors Rickover referred to way back in 1953.
Basically, anyone can say that their reactor is way better than others that people have tried, but there’s no reason to believe them even a little until they can point to one that’s operating and show you how well it works. This is easy to forget in a world with significant VC energy funding.
Some countries have written legal definitions of advanced reactors as part of providing government support to some reactors but not others. For example, the USA’s Nuclear Energy Innovation and Modernization Act defines advanced nuclear reactors as follows:
The term advanced nuclear reactor means a nuclear fission or fusion reactor, including a prototype plant (as defined in sections 50.2 and 52.1 of title 10, Code of Federal Regulations (as in effect on the date of enactment of this Act)), with significant improvements compared to commercial nuclear reactors under construction as of the date of enactment of this Act, including improvements such as
As described in the reactors page, there are literally millions of different types of reactors. Which ones are advanced and which ones are not is pretty subjective.
graph TD TRL([Choose\ntechnology\nreadiness\nlevel]) --> High --> Construction TRL --> MedT[Medium] --> Construction TRL --> Low --> Construction Construction([Choose\nconstruction\nstyle]) --> Modular --> Size Construction --> Stick --> Size Size([Choose\nsize]) --> Micro --> Cycle Size --> Small --> Cycle Size --> Medium --> Cycle Size --> Large --> Cycle Size --> Gargantuan --> Cycle Cycle([Choose\npower cycle]) --> Rankine --> Moderator Cycle --> Brayton -->Moderator Cycle --> Stirling -->Moderator Cycle --> Piston --> Moderator Cycle --> Chemical --> Moderator Cycle --> Thermionic --> Moderator Cycle --> Ion[Ion capture] --> Moderator Cycle --> Inturbine[In-\nturbine\ncombustion] --> Moderator Cycle --> Other --> Moderator Moderator([Choose\nmoderator]) --> MWater[Water] --> FFM Moderator --> MHW[Heavy Water] --> FFM Moderator --> None --> FFM Moderator --> Graphite --> FFM Moderator --> Beryllium --> FFM Moderator --> MOrganic[Organic] --> FFM Moderator --> Hydride --> FFM FFM([Choose\nfuel\nform]) --> Oxide --> FC FFM --> Metal --> FC FFM --> Nitride --> FC FFM --> Carbide --> FC FFM --> TRISO --> FC FFM --> MSF[Molten salt] --> FC FFM --> LMF[Liquid metal] --> FC FC([Choose\nfuel\ncycle]) --> LEU[LEU converter] --> Coolant FC --> NU[Natural uranium\nconverter] --> Coolant FC --> HALEU[HALEU converter] --> Coolant FC --> HEU[HEU burner] --> Coolant FC --> PU[Plutonium burner] --> Coolant FC --> UPU[U-Pu breeder] --> Coolant FC --> THU[Th-U breeder] --> Coolant Coolant([Choose\ncoolant]) --> Gas --> CO2 Gas --> Nitrogen Gas --> He Gas --> Air Coolant --> Water --> LW["Light\nwater"] --> BWR LW --> PWR LW --> Steam Water --> HW["Heavy\nwater"] Coolant --> LM[Liquid Metal] --> Na["Sodium/\nNaK"] LM --> Lead["Lead/\nPbBi"] LM --> Mercury Coolant --> Salt["Molten\nSalt"] Salt --> Fluoride Salt --> Chloride Coolant --> Organic Coolant --> Sulfur Coolant --> LH["Liquid\nHydrogen"] Coolant --> HP["Heat\nPipe"] Coolant --> OTH["Other\n(Sulfate,\nplasma,\ndust)"]
Given these, many useful quantities can be computed for comparison, such as mined uranium and SWUs needed per kWh.
|Make||Organization that designed the plant||KEPCO, EDF, Westinghouse, GEH|
|Model||Trade name of the reactor type||APR-1400, AP1000, ABWR, BWR-4|
|Plant||Individual plant name (if applicable), N/A if just talking about a design||Diablo Canyon|
|Unit||Individual unit name in a given plant (if applicable), N/A if just talking about a design||Unit 2|
|Rated thermal power||Peak thermal power of the core||To know how much heat it can make, roughly correlated with size||MW (thermal)|
|Rated electric power||Peak electric power of the power conversion cycle (if any)||To know how much electricity it can make, important for end use||MW (electric)|
|Utilized heat rate||How much thermal power is utilized for a productive process (e.g. industrial heat, desalination, hydrogen)||To know how much of the total power is being actually used rather than wasted to ambient||BTU/hour (thermal)|
|Date announced||When the design/reactor was first announced||To know what era it's from, to make timelines||1962-05-12|
|Date licensed||The date that license to operate was first granted (blank if none)||To know if and when it has regulatory certification||1962-05-12|
|Date operational||The date that the first of these first entered production||To know if and when it started operating||1966-05-13|
|Availability factor||Fraction of the time that the plant is not in an outage (e.g. at any power). Not to be confused with capacity factor.||To know how long outages are||percent||93%|
|Average Power Fraction||Average fraction of total rated power that is generated when operational.||To know how much load following is occurring, and to compute total capacity factor||percent||96%|
|Fuel form||What the fuel is made of||Basic||UO2, carbide, molten salt, metal|
|Moderator||What moderator (if any) is used in the core?||Basic||Water, heavy water, graphite, beryllium|
|Average reload fissile fraction||Average fissile fraction of reload fuel in equilibrium (enrichment)||Important factor in fuel cycle practicality, sustainability, and economics||Mass percent||3.2%|
|Average initial fissile fraction||Average fissile fraction of initial core (enrichment)||Important factor in fuel cycle practicality, sustainability, and economics||Mass percent||4.5%|
|Initial heavy metal mass||Total heavy metal mass loaded into reactor at startup||Combined with fissile fraction, determines cost and resource needs of a new unit||metric tonnes of heavy metal (e.g. of uranium)||20 MT|
|Average reload HM mass||Rate at which heavy metal mass is loaded into the core.||Sustainability and economics assessments||metric tonnes of heavy metal per full-power year||3 MT|
|Initial fuel source||Where the initial fuel is coming from in the fuel cycle||To understand the fuel cycle||Mined, recycled, downblended|
|Reload fuel source||Where the reload fuel is coming from in the fuel cycle||To understand the fuel cycle||Mined, recycled, downblended|
|Average core height||Average height of the core||To know the size||m||4.2 m|
|Average core radius||Average radius of the core||To know the size||m||4.2 m|
|Cycle length||Average time between startup and shutdown (e.g. for maintenance and/or refueling)||Needed for economics comparisons and operational assessments||months||18 months|
|Primary coolant||What material transfers heat between the splitting atoms and the first heat exchanger/steam generator?||Basic||Water (PWR and BWR), sodium metal, helium, enriched chloride salt|
|Secondary coolant||What material transfers heat between the first heat exchanger and the second heat exchanger/steam generator (if applicable)?||Basic||Water (PWR), sodium metal, fluoride salt|
|Tertiary coolant||What material transfers heat between the second and third heat exchanger/steam generator (if applicable)?||Basic||Water, nitrate salt|
|Quaternary coolant||What material transfers heat between the third and fourth heat exchanger/steam generator (if applicable)?||Basic||Water|
|Primary coolant pressure||The average pressure of the primary coolant.||To understand the containment/cooling needs after depressurization||kPa||16000 kPa|
|Power cycle||What kind of power conversion system is in place?||To know overall capabilities||Steam Rankine, Gas Brayton, Stirling, thermoelectric, endothermic chemical reaction|
|Average coolant temperature at plant output||Average coolant temperature at inlet to turbine (or other process)||To know which end uses of the heat are available, and to know material choices||°C||500 °C|
Special thanks to Brett Rampal and Adam Stein for discussing this with “us” here.