Wednesday, June 17, 2009

Large vs. Small LFTR Reactors

Large vs. Small Nuclear Reactors

A comradely debate and discussion has been going on for a number of years over on the web site, the pre-eminent web site for all things concerning the Liquid Fluoride Thorium Reactor.

This contribution to that discussion will focus on the LFTR but a few other items of important to note.

This week, Babcock and Wilcox announced their new mPower reactor. It's a light water, pressurized water reactor like almost all currently running reactors but they are very, very small: 125MW modularly build, sited underground, reactors. B&W is suggesting that costs will run between $4,000 and $5,000 a KW installed, or, about $1 billion and change for one of these modules.

B&W joins a host of other companies and proposals for small reactors that include:

Hyperion Power Generations [] Hyperion Power Module, designed for process heat (approx 70MW thermal) and 30 MWs of electricity if hooked up to turbine generator stet.

Toshiba's 4S (Super Safe, Small and Simple) reactor. [] This power plant is designed to provide 10 Megawatts of electrical power.

Even the Russians have developed one off of their advanced lead-cooled submarine reactors: The The SVBR-100 reactor. []

Lastly, but certainly not least, Rod Adams, from Adam's Atomic Engines, also has a very small reactor design using a brayton cycle gas turbine with nitrogen as it's cooling source for the reactor and the propulsion for the turbine.

Modular Construction

All these reactors offer modular construction, transportability of those modules or even whole units to a siting, simplified and passive intrinsically safe designs, and affordability, items that for the most part the larger 1000+ reactors currently being deployed cannot, for the most past, offer.

Before getting into the question of 'large' vs. 'small' reactors, we need to parse out what the various reactors can be used for based on their 'product' and use and how the LFTR fits into all this.


The LFTR is unique from all of the above because it is amazingly scalable...there is no real downward or upward limit to the size or use a LFTR can be employed in. Say, from a small LFTR 'battery' of 20 MWs to a large, base load plant offering 1800 MWs gross base-load power to the grid.

It is my contention that there will be a 'market' for all these sizes. We should first review what these markets are.

On the smaller end, the LFTR, as a high temperature reactor, can provide process heat. A small chemical plant, requiring thousands of tons of steam an hour, can use a LFTR to provide this heat and, to electrically power the plant. A slightly larger version may be able to provide power and vast qualities of heat to an oil refinery or a tar-sands operation thus providing carbon-free process heat to what otherwise would be a huge carbon-spewing operation.

These smaller LFTRs, from 20 to 200 MWs could provide, also, site specific load balancing for a grid that has a lot of load in place but generation many hundreds of miles away. Using a 200 MW LFTR to 'anchor' the grid would be very helpful to any utility. Additionally these smaller LFTRs could be plopped down in various transmission substations to provide quick, peaking power or variable load changing that responds to frequency changes throughout the day.

Additionally, along the process heat scenarios, these small and, larger LFTRs can be used to cheaply crack sea water into various products including and most desirably, hundred of thousands of cubic meters of fresh, potable water for drinking and agriculture, thus allowing a huge increase in agricultural output in drier climates, like California, Egypt or Tunisia. Thus electrical generation would be, or could be, the co-generation product of such plants. Additionally, another such product from process heat could be the cracking of hydrogen from water using high-temperature electrolysis, thus providing yet another alternative fuel for automotive transport.

Larger LFTR units could be would be used for base-load generation. Phasing out gas and coal plants with big 1000+ MW units.

There are many uses for all sizes of LFTRs that are all designed basically the same. has papers and discussion on how all this works, so I won't go into basic LFTR technology here.

One thing that is important for this discussion to note, however, is that LFTRs, from the get go, are cheaper to produce, having a much higher power density than any currently running or under-construction Generation II or III Light Water Reactors. From the reactor core itself to the turbine, size is about 1/2 to 2/3 smaller, thus allowing for a cheaper, and therefore far more efficient, product based on size/cost per MW output. We are looking at, generally a similar ratio in cost reduction. the meat of the issue

It is my contention, or thesis, that there is a use for both the smaller scale, sub-300 MW LFTR units AND the larger, up though 1800MW LFTRs as well.

The argument is poised this way: is it cheaper (safer, easier, efficient, etc etc) to build, for example, 15 100 MW LFTRs vs one 1500 MW LFTR to achieve a 1500 MW requirement for a single location? This is the heart of the debate.

Charles Barton over at and a keen observer of nuclear and 'renewable' energy costs. Many nuclear bloggers have as well. I'm not an economist, financial expert or engineer. My experience is simply one of a interested observer, and commentator, on energy issues. Charles is an advocate of the LFTR deployment being one of small reactors. He has many blog posts on this question and I urge all left-atomics readers to go to his site and look for these posts.

Advantages of Smaller LFTRs...

So...what ARE the advantages of a small, sub-300 MW, or sub-100 MW LFTR? Because the overall size of a LFTR is at least 1/2 the size of the equivalent LWR to start with, and these smaller lifters are 2/3 to 1/10 the out put, small LFTRs may able to be transported, in total, on three tractor-trailers or rail cars (reactor core/housing, turbine, generator). Given that construction costs of large, LWR amount to almost half the costs of a large reactor today, this is a tremendous savings.

Additionally, almost the entire module assemblies may well be assembled in a factory, on a production line similar to that of the building of passenger and cargo aircraft today. Production costs for smaller, but quantitatively greater, components ARE the cheaper form of production based on economy of scale.

The reality, however, is that even for larger reactors of the LFTR variety, almost all their components are also factor built, just like in today's' fleet of reactors. There is something of a 'production myth' that these large reactors are somehow built more primitively. Almost every single component in a modern nuclear reactors is built 'on a line'. But even small pumps, motor, controls, etc are built 'by hand', albeit in a factory. A 100 HP pump is hand assembled for the most part, albeit the parts that compose the whole pump are more likely to be manufactured on a true assembly line process.

I suspect as we parse out the true production costs for larger and small components, even the smaller ones for the small LFTRs that the costs are not that different from the larger units.

The advantage for the smaller LFTR is that many more modules for different aspects of the plant can be cobbled together in a factory as opposed to hand assembled on site. Generally, the rule holds that a system that comes 'ready-to-install' it is cheaper than one assembled by hand on site. A CO2 fire suppression system is an example of this. While the pipe runs to each piece of electrical equipment has to be hand run, the CO2 discharge assembly, composed of dozens of small, say 1" diameter, pipe runs, regulators, pilot and stop valves, on unit that is, say, 10 feet by 10 feet, can easily be built in a factory and shipped to the site. But in a bigger plant, where you need pipe discharge valves and runs that use use, say, 2 and 3" diameter pipe and valves, and is 20 feet by 15 feet, then assembly on site may have to occur. Thus an increase in expense.

But If...

But if...and this is the big "IF", this bigger assembly which can service a 1000 MW plant is more expensive per unit, say by a factor of 3 (for the labor it takes to assemble it on site as opposed to a factory, and the large individual sub-components cost more as well), but you need 10 of the smaller cheaper assemblies for the 10 separate LFTR units, then those cost savings for the 10 smaller units disappear and are actually more expensive by a factor of 3.

So, what all of us need to do, and it would help if actual operations engineers, construction engineers, and manufacturing engineers chimed in here, is actually parse out the true costs of a complete, say, 100MW LFTR and that of a 1800MW LFTR. I argue that it will be *impossible* to determine until all sized units are built in mockups to scale, during the R&D that precedes actual deployment. We simply will not know.

Some more things to think about. A big expense for any reactor and turbine generator set are controls. This including things like monitoring radiation, temperatures throughout the reactor-to-heat exchanger loops to the turbine and, of course, volts/amps/watts on the generator. A generator, regardless of the size, has a voltage relay device that reads the system voltage and the voltage of the generator. A set of leads from the high and low side of the transformer banks "potential transformers" (PTs) runs back to a relay and monitor in the plant's control room. There are *hundreds* of these sorts of systems on any modern power plant, regardless if they are geothermal, conventional steam plants or hydro units.

The PTs generally are all the same size and installation uses the same methods. Their testing, 'stressing' and maintenance are all the same based on conditions at the plant. So, regardless of the size of the LFTR, they will all get the same sort of PTs and all the costs associated with them. So, for 1500 MW plant, the costs for 15 100 MW LFTRs for the PT sets required are *likely* to be 15 times more expensive than for the 1500 MW unit (to be fair, there may be a larger redundancy for the larger units as they often have more than one transformer bank). But even if divided by 2, the costs, or "economy of scale", is now reversed and favor the single larger 1500 MW unit.

And this, fellow nukes, is my point. All these factors have to be taken into account when supplying what the customer wants in terms of gross MWs installed in a single location.

To be fair, this is VERY, very simplified presentation of counter-positions. But this does need to be seriously parsed out, eventually.

I believe the real advantage of the smaller units will be it's flexibility in installations, where they can be located, how, etc. Many times utilities want the bigger units because the are compelled by many reasons to group their "MWs together" in one big unit. The smaller LFTR modules can be "distributed" for, in some/many cases, a more reliable grid. Thus the same 1500 MWs the big public utility may want can now be distributed over a greater, and therefore more reliable area. Because the price difference and environmental impact for doing this with conventional fossil plants was prohibitive, you did not see this occur. Thus the LFTR gives advantage because if it's "infinite scalability" to distribute it's power production.

Secondly, and more importantly, while I will continue to put an "equal sign" between the big and small versions of the LFTRs that will be deployed in the future, for many, perhaps most, parts of the world, the smaller LFTR versions will be highly desirable. Many countries have electric grids that have, because of the legacy of colonialism and imperialism, war and revolution, dilapidated, incomplete or basically retarded development and mass under or non-electrified sections of their countries. This is one of the reasons why India is still interested in nuclear energy in *under* 700 MW units.

A grid that is relying on 200 MWs of diesel powered in 10 locations and subject to blackouts, fuel shortages, can add, for example, as part of a rural and small town electrification program, a set of, say, 3 100 MW LFTRs to boost over all capacity to 500 MWs while load increases from 200 to, say, 300 over a year or two. Multiple non-joined grids could be developed this way and then joined as transmission finally ties the country or region together. Smaller, 50 MW LFTRs can be installed incrementally. Eventually you'd have a larger, regional grid composed of about a dozen or more variable sized LFTRs. As the economy improves because of the addition to the *physical* economy of the nation gets stronger, larger LFTR units could be installed in more centralized locations with the smaller ones previously installed used to balance frequency/voltage and provide peaking power.


Marcel F. Williams said...

I think if you can build at least six or more large (1GWe plus) nuclear power plants at one site, then they would have an economic advantage over building small 150 GWe or less centrally manufactured reactors since the large reactors could take advantage of both economies of scale and mass production. Subsequent reactors should be a lot cheaper than the first reactor built on site (first of a kind cost).

However, such large nuclear sites would only be advantageous if they were mostly producing hydrocarbon synfuels.

But if we're only going to build nuclear reactors purely for domestic electricity production then small centrally mass produced reactors probably have the economic advantage.

Jason Ribeiro said...

Reactors that come in the current jumbo size are only suitable for certain areas where cooling resources and grid infrastructure can handle. There are so many "small" sized coal plants in this country that could be replaced by say 1-3 modular smaller sized nuclear units so that a campaign to rid us of coal would be much more feasible.

But of course there is also the regulatory infrastructure issues which would need to change to make this is a reality.

Left Atomics said...

Don't forget, Jason, that the LFTR, regardless of the size, using only about 1/3 the amount of cooling since it doesn't need a large heat sink/or delta t of temperature co-efficient. The Brayton cycle engines need very little cooling in general. This makes the LFTR, of any, size, far more water efficient than anyother type of reactor.

Left Atomics said...

There is not question that a large number of larger reactors can save on Balance-of-Plant resources. But as Jason points out, not all power is bested sited per this criteria.

The advantage of smaller units is that they can be used far more effectively for grid blanance, peaking power, voltage and frequency control when used closest to the load or decentralized.

The ideal grid, IMHO, is one where you do have a number of large "nuplexes" but balanced with a diffuse spread of large and small reactors through the load area.


Joel Upchurch said...

The trouble is that the NRC distorts the economics, because the site license isn't any cheaper for a small reactor.

With large reactors, if you build enough of them, can have economies of scale. The AP1000 has a modular design, so much of the components would be built in a factory in any case.

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jane said...

Distributed energy is best; so factory build and sealed and shipped at less than shipping container size is the only way to go; centralized combos have had their chance and blew it; end of story

David said...

A 125 MW power plant that cost a billion dollars has about a ten year payback, depending on the interest rate of the funds, at a 10cent KWH retail cost.

This means that people with funds to invest will be able to totally recoup that investment in a reasonable time and will gain a strong profit on that afterward.

A smaller unit makes more sense because a modular small unit needs less capital than a large unit and can begin producing electricity sooner so that the time between investment and return is much less.

Also, if we use a distributed system, the line losses can be eliminated or reduced considerably so that a 125 MWe reactor place close to the point of use will be the equivalent of a 300 MWe plant at a distance.

In this way 7 small 125MW reactors could replace a 2000 MW large reactor for far less cost, faster time to initial use, and better load following. It also distributes the jobs involved.

The main problems here are regulatory. Can and will the NRC allow such a distributed system?

This kind of investment would attract capital if the risk of government regulations changing while the plants are built could be eliminated.

Economies of scale have more to do with volume manufactured than with the size of manufacture.

Also, because a small power plant about 100MWt is about the size needed to power a ship or other large vessel, the potential market for a smaller size could be much larger than the electricity market. This is Rod Adam's contention.

I think it is a valid contention. This scale of production will compete very well on a price basis with any fossil fuel, leaving the technical challenges of U233 as the main issues.

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I also used the Boeing example and MIT's modularization of the pebble bed reactor in the blog
but more R&D is needed on the LFTR to validate your idea. Are you and Kirk Sorenson able to influence the direction of the Gen IV international effort on molten salt reactors?
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John in the Lot said...

In our collective enthusiasm for modular LFTR designs we should not forgot that a major objection to nuclear energy from the green lobby is the waste issue. Among some of my green acquaintances this seems to be as important as the risk of explosion associated with PWRs. Now I know that LFTRs produce enormously less radioactive waste material, which has a much shorter half-life than the waste products of the uranium plutonium fuel cycle, but when smaller distributed reactors are proposed for process heat or desalination, what about the decommissioning issues. Process industries respond rapidly to market changes and are very cost sensitive. Their life is often relatively short and plants open and close depending on the demand for their products and their profitability. If small LFTRs are used to power such industries there is likely to be a significant number of shut down nuclear plants to manage. The ORNL MSRE plant required a highly expensive decommissioning project to make it safe many years after it was shutdown. It would significantly skew the economics of process heat reactors if the decommissioning costs were included. Unless, of course, decommissioning can also be tackled in a more modular way!

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The manufacturing process lends itself to repeating operations. It is very challenging to run a six-sigma/lean operation in a one-off/job shop/custom configuration operation. The opportunity for and isolation of error grows with the Root of the Sum of the Squares. Simply - the more parts, the more opportunity there is for error. Diminishing Returns would play the key role in scalability. Say 1kW units can be bundled this way to 500kw before losses overcome benefits. These breakpoints would determine module sizes or Product Families - think 'AAA' 'AA' 'C' 'D' batteries. Manufacturing is an exercise in Eating the Elephant one bite at a time. The operations are broken into 'bite sized' pieces to manage complexities, then can be further modified to balance operation timing cycles to produce at rate/on-demand. Personally I'd love to be the Manufacturing Engineer over development of this kind of power generation. The advantages simply out weigh the disadvantages.

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