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What is an Advanced Reactor?
People and laws mention 'advanced reactors' all the time, which are said to have improvements over non-advanced reactors. This page breaks down the facets of advancement that are being referred to.
nick
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2023-04-16
/img/reactor-type-graph.png

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]({% link reactor-history.md %}), the term is somewhat misleading and complex. Depending on who you talk to, advanced reactors can mean a number of quite different things:

Definition 1: Reactors that incorporated hard-learned lessons from the past into the design

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:

  • GEH's Advanced Boiling Water Reactor (ABWR)
  • Westinghouse's Advanced Passive 1000 (AP1000)
  • KEPCO's Advanced Power Reactor 1400 (APR-1400)

Definition 2: Reactors that, once built, could theoretically have extended capabilities beyond modern LWRs

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:

  • Ability to get more energy out of any given mass of nuclear fuel by [breeding plutonium or U-233]({% link recycling.md %})
    • [Uranium-Plutonium breeders]({% link fast-reactor.md %})
    • [Thorium-Uranium breeders]({% link thorium.md %})
  • Ability to reach higher coolant temperatures to:
    • Have higher heat-to-electricity conversion (thermal efficiency)
    • Supply industrial heat to replace fossil heat sources in hard-to-decarbonize chemical/industrial processes
  • Remove [afterglow heat]({% link decay-heat.html %}) indefinitely after shutdown without any backup power required to improve safety in extreme conditions (e.g. large regional power outages). This generally requires better connections to ambient heat sinks and/or special coolants like liquid metal or molten salt.
  • Ability to be constructed without as many schedule delays or cost overruns, e.g. by incorporating elements of modular construction
    • Large equipment module built in factory and installed at site (e.g. AP1000 modular construction)
    • Reactor systems built in factory and shipped to site and installed in field-constructed buildings (e.g. NuScale SMR)
    • Entire plant systems built in factory and rail/truck shipped to site for turnkey operation (e.g. microreactors like the Army's ML-1)

Generation-IV vs. Advanced

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.

Advanced reactors vs. advanced reactor concepts

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]({% link rickover.md %}), 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.

{% include rickover-memo-excerpt.md %}

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.

Legal definitions of Advanced Reactors

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:

USA NEIMA's definition of *advanced*

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

  • additional inherent safety features;
  • significantly lower levelized cost of electricity;
  • lower waste yields;
  • greater fuel utilization;
  • enhanced reliability;
  • increased proliferation resistance;
  • increased thermal efficiency; or
  • ability to integrate into electric and nonelectric applications.

Chart of reactor design choices

As described in the [reactors page]({% link reactors.md %}), there are literally millions of different types of reactors. Which ones are advanced and which ones are not is pretty subjective.

{% include_relative _reactor-types-mermaid.html %}

Useful reactor metric inputs

Given these, many useful quantities can be computed for comparison, such as mined uranium and SWUs needed per kWh.

{% for section in site.data.metrics %} {% for metric in section.vals %}

{% endfor %} {% endfor %}

Metric Definition Purpose Units Examples
{{ section.name }}
{{ metric.name }} {{ metric.description }} {{ metric.why }} {{ metric.units }} {{ metric.examples }}

Special thanks to Brett Rampal and Adam Stein for discussing this with "us" here.