Economies of Scale in Nuclear Power
Energy from Thorium blog cites Rod Adams in saying Small is better for getting down the nuclear power experience curve. I had my own comment.
I hit on these factors: Thermal efficiency; operating costs/kwh; materials cost per Kilowatt; Lower fuel costs via higher burnup rates and simpler fuel cycles; Lower engineering costs per Kwh via repeatable and simplified design. I said "It may be neither big nor small that is the issue but - repeatable, simple, high efficiency /high temp, high power density, inherently safe/easier to run, better fuel burnup - that are the factors. If a smaller design hits those points - then it wins."
It occured to me that many are touting solar and wind as CO2 mitigation solutions, and are expecting an 'experience curve' and technology improvement benefit in these technologies to make them cost-competitive. They are not economically competitive today. Yet nuclear technology could be on such a curve, although it's 1970s technologies like PWR and BWR that are the workhorses even today for nuclear reactors. Nuclear's future may lie with different technologies: Pebble-bed, molten-salt and lead-cooled reactors, for example. The Energy from Thorium blog has a lot of outside-the-box thinking about nuclear power that may be essential for a 21st century nuclear power technology base.
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Small reactors can be built in factories and transported to working sites. Large reactors must be custom built on site. All of the points you raise are points whichI intend to address in subsequent posts. My intent is to argue that small LFTRs are capable at operating at far higher levels of Freedom's thermal efficiency that current large LWRs, That materials costs can be substantually lowered by by the use of exotic aero-space materials in reactor construction, plus the compactness and safety advantages of the LFTR requires smaller and less robust structures. The LFTR has a burnup rate of 98%, at any size. There are considerable potentials for lowering operating cost, not the least which is a requirement for fewer operating personnel. Serial production of small reactors in factories would lead in urn to serial production of standardized parts.
Factory serial production of reactors would distribute engineering cost over hundreds and even thousands of reactors.
Thanks for coming to my site!
I am today reading up on STAR-LM and other lead-cooled reactors. I am thinking that such technology is the way to go. the amazing advantages in safety of a liquid pool reactor versus high-pressure vessel is clear. The idea of a liquid fuel is fascinating and I see advantages in it. I have many questions and will take a look at your blog and followup.
I must point out that the USS Nimitz, the nuclear-powered Navy aircraft carrier, was refueled 4 years ago for the first time. It went into service nearly 30 years ago. One refueling each 25 years...that is energy efficiency and independence!
The high temperature gas reactors that fascinate me provide the opportunity for significant cost reductions by taking advantage of several of the concepts that you mention.
The efficiency of any heat engine has a strong relationship to the total temperature difference available in the cycle. As far as I can tell, the graphite moderated TRISO based fuels for pebble beds and prismatic cores allow the highest temperatures of any proposed cycle. Both the lead cooled reactors and the molten salt cores that Charles Barton and Kirk Sorensen discuss have somewhat lower temperatures at the top end of the cycle.
With gas cooled reactors using direct cycle gas turbine heat engines, it is also possible to eliminate a number of expensive operationally challenging components like heat exchangers and after shutdown heating systems. Both liquid metal cooled and fluid core reactors still include those components that might add significantly to the initial capital cost and the long term operations and maintenance costs.
With gas turbine (Brayton cycle) heat engines, the turbine exhaust temperature is still high enough for a bottoming Rankine cycle similar to the ones used in modern combined cycle plants. If process heat is needed, a better choice might be a cogeneration plant that uses the turbine exhaust heat to heat a secondary heat distribution system.
I love the fact that more and more people are beginning to challenge the bigger is better mantra and thinking of ways to apply the lessons from other industries to nuclear fission power. Please understand that I am not trying to criticize the other ways of doing this, just to explain why I have chosen the course that Adams Atomic Engines, Inc. continues to pursue.
BTW - if any of you do develop a fission system that can provide a turbine inlet temperatures of 800-900 C, let's talk. My main effort is to work on lowering the overall cost of constructing and operating the BOP systems. That is where my real interest lies.
" As far as I can tell, the graphite moderated TRISO based fuels for pebble beds and prismatic cores allow the highest temperatures of any proposed cycle. Both the lead cooled reactors and the molten salt cores that Charles Barton and Kirk Sorensen discuss have somewhat lower temperatures at the top end of the cycle."
In looking at the literature, the early experience with lead-cooled reactors is limited to Russian experience, and corrosion was a factor limiting temperature to around 550C. Now, with newer research studies, there are paper designs going higher, including to temps like 800C for hydrogen production. there are corrosion controls and methods, eg, SiC or Aluminizing or use ZrN or TiN, or oxide control, that can take you up to higher temps, and lead itself can go to 1700C before boiling so is an incredibly stable environment for nuclear reactor, beating sodium, PWR, BWR and even HGTR in safety margins. prototypes and experience is what is needed to prove it out.
Further, I've read some ICAPP presentations that indiciate a 650C outlet temperature combined with a supercritical CO2 turbine cycle can acheive 48% efficiency, which is equivalent to the efficiency of the HGTR and helium at higher temperatures.
So higher temperatures is a key thing but not the only thing. How many heat exchangers? Good advantage to gas cooled, but the flipside disadvantage is that there is one more barrier to radiation release in lead-cooled and lead is a great gamma barrier.
"if any of you do develop a fission system that can provide a turbine inlet temperatures of 800-900 C, let's talk. My main effort is to work on lowering the overall cost of constructing and operating the BOP systems. That is where my real interest lies."
Myanswer: Yes, lead-cooled systems can get that high in temp, there are hydrogen-gen designs at that level. it needs to be proven out but the ideas are out there. ANd using some tricks where the vessel walls will be much lower than that outlet temp in operating conditions can keep the temp issue lessened.
And here's the good part - we dont even need 800-900C to crack 50% efficiency! 700C plus supercritical CO2 is sufficient. The architecture of such a system? There are many small modular lead-cooled systems - ENHS, STAR-LM, LSPR, PEACER, that leverage the modular concepts for various reasons... And for a larger configuration, Look here:
http://www.inspi.ufl.edu/icapp08/program/abstracts/8309.pdf
I see distinct advantages to different types of reactors. HGTR and pebbles and/or ENHS are best for proliferation. Lead-cooled are very flexible and good at burning actinides and/or having super-long burnup cycles (look up 'CANDLE burnup'), so they can help us minimize nuclear waste and/or recycle SNF.
In any case, nuclear is more than PWRs.
Freedom's truth:
One thing that I have learned in 30+ years in and around government is that you can find many reports and papers with "optimistic" numbers presented as reality.
When it comes to building machines in series production, you have to have a bit more than projections; basically you have to be like those wonderful people from Missouri who ask "show me."
There is a history with the high temperature gas reactor fuels that dates back to the early 1960s. You can see where the initial fuel designs had weaknesses and understand what the engineers did to correct those. You can find documentation of the testing and the post reactor physical evaluations showing detailed photos of the particles after various amounts of exposure and fission.
800-900 C is well within the operational experience envelope; testing has also be done up to about 1300 C with reasonably good results and accident analysis shows that damage only begins at 1650 C for an extended period of time. Complete fuel breakdown does not start until 2500-3300 C. When it comes to the working fluid - the gas is already boiled and has no other state to reach.
I can also point to tens of thousands - perhaps millions - of Brayton cycle gas turbines operating at even higher temperatures than those used by Adams Engines. Those machines use air and a mixture of air and combustion products, so I am pretty confident that I understand what will happen chemically and physically with N2 as the working fluid in our machines.
Though I am interested in research on a personal level, when it comes to building machines I need for the research to be essentially complete with results in hand before I can even order the detailed design for the machines that the factory will build. Changes after the fact are simply too expensive and risky.
Keep up the good work in surveying the literature, but keep a skeptical eye and dig to find out the complete results from the experimentation supporting the papers.
freedom's truth:
PS - I am not a big believer in the concept of maximizing efficiency, especially when the process requires additional components or stretching physical limits.
Remember, the big cost driver in today's nuclear systems is the capital cost - compared to fossil fuel systems, nuclear fuel is cheap, cheap, cheap.
Rod, thanks for your comments and thoughts. I'd say the one thing going for lead-cooled in real-world is the Russian sub experience, which in turn shows lead-cooled (LBE for them more specifically but I think lead is superior because LBE create Polonium) can work as an inherently safe and in small reactor format.
"Brayton cycle gas turbines" is the way to go.
"I am not a big believer in the concept of maximizing efficiency,"
Then why the interest in 800-900C? The main benefit is higher efficiency, which in turn helps capital cost/kilowatt.
Bit if your main point is simpler=better, I agree.
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