NGNP aims to expand nuclear fission out of its electricity producing niche (box)
The NGNP Alliance recently published a thought provoking blog titled Energy Vs. Electricity and Why We Care that clearly explains the basis for their interest in using high temperature gas cooled reactors. That group of far-sighted organizations was formed in recognition that the energy market is far larger than just producing electricity.
They believe that higher temperature reactors offer a good path for enabling fission energy to serve needs in other segments of the energy market, bringing its energy density and emission free nature to applications like industrial process heat and enhanced resource recovery.
If we moved our electricity production to 100% carbon free sources, like nuclear, hydro, and renewables, we would reduce the use of carbon fuels by only 25%. Basically cutting most coal consumption and reducing natural gas by 30%. But we would still be left huge amounts of petroleum and natural gas being used for industrial and transportation purposes.
The NGNP Alliance is looking at a new kind of reactor, called a High Temperature Gas Reactor (HGTR) that can generate high temperature, high quality heat and do it with true inherent safety. That heat could replace coal, natural gas, and petroleum in many industrial processes including chemical and fertilizer manufacture and hydrogen and synthetic fuel production.
I’ve been interested in expanding atomic fission’s role in the energy market for almost as long as I can remember. My early experience in nuclear energy was in using it to propel ships around the world; electricity production was just an auxiliary task for the reactors I learned to operate.
I’ve never forgotten how the Navy’s propulsion reactors directly replaced diesel engines and large, oil burning steam turbines. That still seems to me to be a huge, untapped commercial opportunity, especially in a world that is so often made to tremble in the face of threats to continued oil abundance.
As I pointed out in a recent post welcoming the NGNP Alliance to the pro-nuclear blogging community, the group has recently opened the comment feature of its blog. That is a big step forward for the rather conservative, large-company members of the Alliance. Not only has the NGNP Alliance enabled comments, they have assigned a technically astute moderator who both keeps out the trolls and engages in thoughtful discussion.
I have taken advantage of the rare opportunity to participate in a publicly accessible conversation with people who are working on technology that has quite a bit more than a prayer of moving beyond the paper reactor stage of development. My latest contribution to the discussion thread was in response to a commenter who was concerned about the fact that helium is a difficult gas to contain. His concern is that a seemingly small leak rate could add up to a substantial issue over the life of the plants.
@Praos
I understand NGNP’s decision to use helium, it has a number of attractive properties that resulted in its selection as the de facto coolant of choice for gas cooled reactors sometime in the late 1950s to early 1960s.
Up until that time, the favored gas was CO2, which was the design choice for the British Magnox and AGR reactors. Though no new CO2 cooled reactors have been built in 30 years, the UK still produces about 10-15% of its electricity each year with CO2 cooled reactors. By far, it is the coolant gas with the most run time in nuclear reactors.
There is one thing we already know about that alternative; CO2 breaks down at too low of a temperature to make it useful for the high temperature reactors that NGNP is planning. It’s maximum temperature limit is somewhere close to 600 C.
Designers looking for a better coolant gas selected helium for Peach Bottom, the AVR and for the Dragon HTR. There were promising results in those small reactors. The challenges associated with helium’s physical properties (monatomic gas with very low specific mass) did not make much of an impact until attempts were made to produce much larger machines and to consider using helium as the working fluid as well as the reactor coolant by directly coupling a gas turbine to the reactor heat source.
Then, factors like leakage and the challenge of completely redesigning turbines and compressors (and building up an entirely new supply chain) became much more important.
In my opinion, helium-related technical challenges have been a primary reason why gas cooled reactors have not had much commercial success, despite their promise and despite the fact that GA once had an order book of more than 10 large units, none of which were ever really started. Helium gas challenges are no more insurmountable than the challenge of using light water as a coolant at temperatures high enough to produce useful steam; the difference is that the LWR hill was climbed in the 1950s. That means there is a knowledge base and a supply chain.
I avoid climbing big hills. I’m a lazy cheap skate (actually, I am just not terribly wealthy, so I needed to find a cheaper way around the issues). Early in my Adams Engines days, I determined that nitrogen gas has “good enough” nuclear properties and with the advantage of having aerodynamic properties that are essentially identical to air. Using N2 allows atomic engine designers to take advantage of the vast technology and knowledge base associated with air breathing combustion turbines.
Aside: I discussed this decision in detail in a post titled Nitrogen (N2) Gas Cooling For a Closed Cycle Nuclear Heated Gas Turbine End Aside.
The market application I was interested in serving is different from the one that NGNP is aiming to serve. Their choice of helium makes perfect sense; there are nuclear related challenges with using nitrogen that cannot be solved, they must instead be mitigated. I think the mitigations will be effective; nitrogen’s inherent neutron absorption and activation issues discourage most nuclear engineers from even considering using it as a coolant gas.
In NGNP’s defense, the technical challenge of preventing leaks in a helium cooled reactor can be solved, my hope is that we have gained enough engineering and manufacturing experience in the 50 years since the ill-fated water cooled reactor coolant pump bearings so that NGNP has more success than Ft. St. Vrain.
I have selfish reasons for wanting NGNP to succeed. Not only do I want more nuclear fission power to replace fossil fuel combustion, but I also want regulatory acceptance and a supply chain to be established for TRISO coated fuel. Those tiny particles are a key building block that just might make it possible for another attempt at building Adams Engines sometime in the distant future.
(Note: I have made some minor edits since my original comment on the NGNP Alliance blog.)
Ron,
I had a similar idea, but used a sealed Molten Salt reactor with heat pipes to transfer the heat to a standard gas turbine.It would use TRISCO fuel pellets. The idea is very similar to the atomic powered bomber developed in the 50’s and 60’s. I cannot find a single reason or problem that will prevent this concept from working. Furthermore the design is very compact which should limit construction and material costs. The unit will air cool in case of an accident and requires no off-site power or ECCS.
My only problem with proposed gas cooled reactors is the size. Gas cooled reactors have very low power density which provides many safety advantages, but the size will have a very negative impact on costs.
GTMHRs coupled to a hydrogen production plant, other SMRs for production of fresh water and district heating. ‘Like’
There are two issues here: the huge potential to apply fission to process heat: refining chemicals, Portland cement production, steel making (don’t know if HTGRs can get up that high, however, though in electric form they can, thus reducing the need for coking coal — maybe; desalination and sewage treatment.
The other issue is the motive gas used in a Brayton cycle turbine. Rod is correct that the turbine tech already out there in terms of blading lengths, casing strengths, etc is already done. What’s not done is the actually *closed cycle* Brayton gas turbine. All tech R&D had been toward combustion turbines that burn gas, diesel and, in the case of Saudi Arabia, raw crude oil. It seems that Brayton tech just makes people run in the other direction.
Cases in point:
The Chinese own HTGR they are building now takes the hot gas and…then they make steam with it to run it through a Rankine once-throught turbine.
Westinghouse, which was working with the large S. African utility on deploying the Pebble Bed Modular Reactor also noted, on Rod’s pod-cast years ago, that the turbine was both their most expensive investment in the project and hardest to overcome. So hard they cut ties with the utility and the project folded.
I’m hoping some entity someplace can really invest in a closed cycle Brayton turbine regardless of the gas they use.
Just on He. Helium is a fossil resource and this is a major problem for a vast deployment of helium cooled SMRs. It was chose originally for the PBMR because of it’s excellent thermal properties AND it being totally inert to radioactivity. I suspect N2 is the same so I look forward to see more R&D on the gas side of this question.
David Walters
@john, You described the PB-AHTR, pebble bed advanced high temperature reactor initially conceived at UC Berkeley. The project has been joined by MIT, UM Madison, and DOE/ORNL. Visit http://pb-ahtr.nuc.berkeley.edu/ for details.
Robert,
Thanks for the info. There are many commonalities. However, my design is simpler, uses no pumps (thermosiphon) or secondary loops and is doubly isolated from the standard gas turbine. It is much simpler and will be much less expensive. No moving parts except the control rods and turbine/generator shaft. No ECCS, just thermostatically controled dampers. A superior design for civilian or military use.
Rod, is there anything going on with NGNP except meetings and press releases. The biggest news is that DOE awarded the industry alliance $1 million, about a factor of 1000 short of being able to accomplish something. I understand the alliance picked the General Atomics design, but is anybody going to build it?
Note that after China announced they had begun construction on their commercial HTGR for 2017 service with a rumored 70% of its output reserved for synfuel production, our passively anti nuclear then energy secretary announced another million for a study of the concept.
Funny how Secretary Chu could spent close to $100B on solar and wind research – ie give the bums all the money they need to build the things no questions asked – but seemed to only have about $250M pa for advanced nuclear the only possible in time solution to AGW.
Maybe Moniz can change it all around but I doubt it.
This century belongs to China. Ironically it was Chu who gave them the keys.
Every time that the issues related to helium (very low MW, very high velocities and compressor/turbine speeds) are considered, I come back to neon. The thermal-neutron cross-section of neon is only about 6x helium’s (0.04 barn vs. 0.007). The atomic weight is 5x greater, nearly as high as air. It cannot break down chemically.
It would seem to solve the issues related to both coolant and working-fluid properties… but it’s not in the running. I’d like to understand why
The NGNP won’t be using helium as a working fluid.
If you say so. But why?
One of the main reasons was that NGNP didn’t feel a helium turbine could be developed within a low risk, reasonable timeframe. Steam turbines are off the shelf.
This says He as the reactor coolant, “steam and/or high-temperature fluid” as the working fluid:
http://www.ngnpalliance.org/images/general_files/HTGR%204%20page%20individual%20040611.pdf
Expensive coolant, lots of pumping losses, high pressure in the reactor vessel.
The advocates of molten-salt coolant seem to have a pretty good case.
@Engineer-Poet
I tentatively agree with you about molten salt having a good case, but there is a fundamental issue associated with that material as a coolant that does not get much play among the enthusiasts.
What happens when you need to perform maintenance on the system that requires temperatures acceptable for human contact? What is the melting point of the salt? How do you get the system cool enough and how do you heat it back up when it is time to start the plant up again. I’m sure these issues have been addressed somewhere, perhaps in those private forums that the LFTR folks like, but as light water reactor specialist who thinks that gas cooled reactors are pretty hot, I just cannot quite get my head around the challenge.
Based on some light research into the field, I found out that, like many other engineering choices, there are tradeoffs. If the fluid has stability at the temperatures I want to use for a closed cycle gas turbine (in excess of 800 C) it has a melting point of perhaps 140 C or greater. (That is way above the boiling point of water and far too hot to touch.)
That means that a complex piping system that moves fission product carrying fluid would be difficult to cool down and reheat because you could not use pumps and conduction for the cool down or heat up.
A molten salt reactor doesn’t need to do that. In stead, it can dump the fuel and coolant – which are the same stuff – together to a holdup tank. Then reactor vessel then is empty of both coolant and fuel. Flush some seperate (clean) salt over it, and you’ve got a quite low radiation dose inside the vessel. Replacing some graphite isn’t hard, compared to shuffling and moving out fuel rods that carry 99% of the radioactivity of the core.
This is a major potential advantage over any solid fuelled reactor, where dumping the coolant would mean overheating the fuel… you could never operate the reactor vessel dry when fuel is in there.
As a bonus, there is no thermal cycling to worry about. Hot manipulation is well established in other industries, such as aluminium and steel.
@Cyril R
Something practical in me says it is not quite that easy. Are there no bends in the pipes and no place where fluid might accumulate? I’ve drained water filled pipes; it’s never as easy as just opening a valve and letting it all flow out.
The flush would have to be done with salt that is clean, but also thermally hot. Where does that come from? What is the heat source? How many flushes are required to get dose rates down?
Hot “manipulation” may be well established, but are you telling me that there is never any role for human maintainers for equipment like valves, pumps, and indication systems? Thermal cycling is not much of an issue as long as you do it at a designed rate so that there is no permanent deformation or working of the materials.
Moving fuel rods might be a bit of a challenge at first, but once we learned how to do it, we seem to be getting pretty good at it. I’ve read about refueling outages lasting as few as 22 days from breaker to breaker.
The design would have to exclude any upward moving bends. That’s obvious.
The flush I’m thinking of is a clean KF-ZrF4 salt, mainly to avoid residual BeF2. ORNL used FLiBe salt. It worked fine for the MSRE. ORNL used electrical heaters to keep the flush salt at temperature, I’m envisaging a buffer salt where all primary loop components are submerged into. The flush is likely a continuous, forced convection system, so just pump till the dose rate is low enough to open the vessel, then drain/pump the flush salt back out again.
There is, it’s just that it’s all being done right now in aluminium electrolysis, iron/steel production, and it was all done in a radioactive environment in the MSRE.
It’s the same for moving hot stuff and keeping hot stuff hot and maintaining the systems. Challenging at first, but perfectly doable, as evidenced by the large number of hot metal industries located all over the world. What helps with molten salt is that everything is at low pressure, so it’s very similar to say an aluminium electrolysis facility (which also handles large amounts of molten fluoride salts at much higher temperatures in fact).
I am not a molten salt cheerleader by any means, but the heat being an impediment to maintenance is just not an issue. There are several processes, most notably in those industries that use molten metal where maintenance is preformed on hot equipment because the time to cool the item is too expensive. Thus there are standard techniques and operating procedures that could be used for molten salt reactors. Combined with commonsense design, hot side maintenance would not be an issue.
Please forgive my ignorance, but it seems to me that the absolute number of metal processing facilities using remote handling and hot manipulation is FAR lower than the number of LFTRs we need. There has got to be some kind of economy of scale associated with the rather expensive systems required to perform the kinds of maintenance that might only be occasionally necessary. Will this equipment be available at all LFTR installations, or will it need to be delivered on demand?
If each site needs the capabilities, does the equipment just sit idle for months to years at a time?
You have to understand that most of the sort of equipment we are talking about is not really that specialized but rather is fairly standard chassis fitted with special tooling and what is known as ‘end-effectors.’ They are used in various hazardous environments other than just hot ones where powering down is something to be avoided. For example I have seen a tractor with the type of arm that one usually sees with a bucket on the end of the sort for digging holes equipped with an apparatus that could be pressed up to a roller bearing in a lumber mill that could press a new bearing in while the line was running.
Considerations like these are not the sexy part of design engineering, and thus are not given much attention when people not directly involved in an industry are looking at it but those that do work in these fields are well aware that all these factors must be taken into account. At any rate it is a given that maintenance equipment is just part of the deal when one is considering a major facility like a power reactor.
Maintenance is the invisible grease that keeps every big system running, and invisible is the way most of those that work in maintenance like it – invisible means you are doing the job of keeping your system running properly. When one does look closely you find that there is not as much idle time as you might think.The downside is John Q Public doesn’t realize you are there most of the time, or realize just how sophisticated the job that you are doing is until something go very wrong and there is an outage or service stops.
@Engineer-Poet
Neon is too rare and expensive for my tastes. It is commercially extracted from the atmosphere where its concentration is 0.0018%. In contrast, N2 also comes from the atmosphere, where its concentration is darned close to 80%.
Ne is absolutely inert, N2 is close enough to inert for government work.
I like nitrogen for reasons that are similar to the reason that Rickover liked water; it is readily available and we have plenty of experience in using it.
Good point about experience, that is also why steam cycles are so popular, even for helium cooled reactors.
But regarding cost of the coolant, how much is it really? With neon costing $100,000/ton in bulk, a 200 (?) ton neon inventory per GWe would cost only $20 million. That’s under 1% of the plant cost. And neon won’t leak out like helium so your makeup costs will be low.
200 tons? At 50 bar, the density of neon would be less than 50 kg/m^3 even at room temperature. I can’t see a reactor core needing more than a few tons of neon even for several GW(th). Multiply by 5 for external volumes and you’re probably still below 20.
IIUC the difficulty with noble gases as working fluids is the high γ forces several intercooling stages in the compression to get good efficiency. Perhaps this could be turned into an advantage, producing low-pressure steam for industrial process heat or district heating. Neon as a coolant wouldn’t have the chemical reactivity issues of water or sodium, and might allow reactors to be built underground below populated areas.
Good, so I was guesstimating rather too much on the safe side. Yes, actually running the numbers (with 1000m3/GWe plus giant steam generators) it’s difficult to see a need for even 20 tonnes.
This proves the point that cost of the coolant inventory isn’t decisive.
By the way, is an group working on neon turbines? This could be a problem.
With a molecular weight of 20, it’s close enough to air that it shouldn’t be a big problem to adapt existing gas turbines to it. The low temperatures relative to combustion turbines and inert nature should make things fairly easy.
Lots of information here, including NRC briefing/training documents regarding NGNP:
https://inlportal.inl.gov/portal/server.pt/community/ngnp_public_documents
wonderful picture – got me reading about operation sea-orbit. Brilliant.
http://en.wikipedia.org/wiki/Operation_Sea_Orbit
is the E=mc2 spelled out with paint or is that the crew? Does anyone know.
It appears to be the crew in dress whites.
You’ve got a better screen than me! But that’s pretty cool if true.
I just used tineye.com to find the biggest copy of the image, and blew it up on my screen.
Argon (Ar) is as chemically inert as He or Ne. It is also nearly 1% of air and an industrial gas. Its neutron absorption is less than that of Nitrogen. It is already being used as the environment over sodium in fast nuclear reactors. Mass of monoatomic Ar is comparable to that of the diatomic gases in the air.
It may be wise to accept it as initial coolant gas till you can get and accept another one.
Funny. I recall Ar-41 being the isotope of concern for any “air accident” in which atmospheric air was introduced into a neutron flux. I do not recall any concern in my training for activation products resulting from neutron absorption in nitrogen, despite the fact that we often used pressurized N2 gas as an inerting gas when performing primary system maintenance and despite the fact that air is about 80% N2 and less than 1% Ar.
It’s got about 1/3 the cross-section of nitrogen (0.675 vs. 1.91 barns), and Ar-41 decays to stable K-41 with a half life of 109 minutes; in other words, essentially gone in a day.
K-41 is stable, but it has a considerable cross section, producing K-42 which is a nasty high energy beta and gamma emitter with a troublesome 12 hour half life.
Yes, but with the tiny cross-section of Ar-40, what’s the rate of production? Minuscule, I’ll bet. The 12-hour half life means K-42 is gone in a week.
I can see two possibilities: either potassium remains mobile in the working fluid, or it doesn’t. If it plates out right away, it is either out of the neutron flux and not a threat, or in the reactor with far nastier stuff. If it’s mobile a “getter” could capture it.
@Engineer-Poet
Despite the relatively large cross-section (which, by the way is an extremely simplified way to describe a complex situation with a single number) nitrogen is still a very simple and cheap solution to converting fission heat into useful motive force.
C-14 has a multi-thousand year half life, but that simply means it is not very radioactive and will not provide much of a dose. It is a manageable issue that allows the use of some terrific machines that have been well tested and are being manufactured TODAY in large quantities.
I’m a lazy cheapskate. I don’t want to do any R&D on argon turbines or spend $20 million to fill my plant when nearly free is the alternative.
Rod, as we discussed before, it’s manageable in today’s reactors because the quantities are very small, because nitrogen is only a trace element in today’s reactor coolants. In a nitrogen cooled reactor you could get over 1 million Curies/GWe-year. That is not easily manageable at all. In fact it is physically large enough (many kilograms) to clog pipes, heat exchangers, the core, and internals.
@Cyril R
Is isotope separation really that simple and cheap? I’m not opposed to it, but I still believe you are seriously overestimating the problem of C-14 production and underestimating the additional cost of using a rare isotope that must be separated from a far more common one.
Would you prefer to spend millions per year to manage the many kilograms of radiocarbon that want to clog up your entire system and risk complete shutdown of the plant? Radioactive solids management is not cheap, especially when it’s clogging up your entire primary loop.
Or would you spend 1% more (at most) on your reactor and have a nitrogen-15 coolant. This could actually save a lot of money in management, removal, and storage of radiocarbon. You will also save money in fuel with less captures to the coolant meaning more power out of your fuel or less fuel for the same power. You could still use the same turbomachinery.
Nitrogen gas is a commercial commodity. Enrichment just means adding a centrifuge or other device to an existing air seperation plant. The only disadvantage is you need a gas, whereas ASUs produce liquid nitrogen. Energy recovery (regenerative) shouldn’t be prohibitive though.
Compared to enriching uranium hexafluoride gas, nitrogen is cheap, doesn’t have to be produced, isn’t corrosive, isn’t radioactive, doesn’t freeze up, isn’t subject to criticality regs or proliferation regs, and can be enriched at lower temperatures.
Gas cooled reactors need loads of tricky expensive uranium enrichment, and they need new enrichment all the time, so I don’t see the problem here. Enriching nitrogen means you lose fewer neutrons, means you need less uranium enrichment.
@Cyril R
Enrichment just means adding a centrifuge or other device to an existing air seperation plant. The only disadvantage is you need a gas, whereas ASUs produce liquid nitrogen. Energy recovery (regenerative) shouldn’t be prohibitive though.
A centrifuge, or a cascade of centrifuges? What is the production rate of each machine? How much does each cost? How many are needed to support the needs of each Adams Engine?
I’m quite willing to consider the suggestion to use enriched N-15 vice natural N if we can get the numbers to compute the overall differences between options. In fact, we will have to be able to make those computations before making much progress towards commercialization.
There are only about 300 megacuries of C-14 in the biosphere (per Wikipedia). Producing megacuries per GW(e)-yr would rapidly raise the concentration to multiples of the natural background level, and it would take tens of thousands of years to return to normal once additions ceased.
There’s nothing particularly special about gas turbines. A different density and ratio of specific heats means a different delta-P and delta-T across a compressor or turbine stage, meaning the size ratio between stages changes a bit and possibly the number of stages changes. Analyzing this stuff is introductory thermo, and I doubt that any gas turbine manufacturer would have any problems with quoting a price for a machine to operate at the mild conditions it would see. I’d bet you could run off-the-shelf turbomachinery on argon or neon at some loss of efficiency due to the off-spec operating conditions.
Can you allow lubricating oil to get into your reactor core? If not, you need a turbine which uses gas bearings. If that’s going to be a custom job, you might as well design for a more suitable working fluid.
I note that if N-15 is converted to C-15 by the (n,p) reaction, it decays right back to N-15 in seconds. This makes it a radiologically superior working fluid to argon, but likely not to neon. It looks like it comes down to price.
Who says we will be releasing C-14 to the biosphere?
@Engineer-Poet
There is nothing special about I-C engines, either. Designing and manufacturing a new variation on an existing design for a multi-megawatt machine can require several billion in capital equipment investment. The manufacturers might amortize that over the first few hundred or even the first few thousand commercial units.
Yes, a closed cycle design might require slightly different bearings. There is a big difference between a tweak and a completely new machine with dozens to hundreds of new parts.
It doesn’t conveniently react to solid products; even CN is a gas. How do you propose to capture it?
Automakers are only spending $500-$600 million for whole new engine plants. GE accepted a contract from India to develop a fighter plane engine, worth just $105 million. I’m finding development cost figures around $60 million for new heavy diesels, such as GM’s new 710G engine.
The blades for the highest performance gas turbines are typically made by investment casting, with each mold individually made. I doubt very much that the demands of a machine operating at 500°C or less need anything like those manufacturing practices. Since the demands on the materials are so low, it should be possible to manufacture the blades and such using commodity machinery and low-cost materials.
The major thermodynamic difference between air and noble gases is the higher Cp/Cv. This creates a greater temperature change for a given change in pressure, so e.g. the size of the compressor stages doesn’t shrink as quickly. There’s nothing mysterious about this, and I’d bet money that the machine can be operated off-spec so long as it’s kept out of the region of e.g. compressor stalls.
@Engineer-Poet
I doubt very much that the demands of a machine operating at 500°C or less need anything like those manufacturing practices.
I expect that the initial engines will operate at an inlet temperature of 800 C or more. The improvement path leads to higher temperatures as we gain more experience with the fuel form.
GE’s combustion turbines are operating at TIT’s up to 1360°C. Materials capable of handling a mere 800°C in a non-corrosive gas stream are not going to be a problem to find these days. They may not even need cooling, which will reduce the manufacturing cost quite a bit (no machining of cooling passages) and also eliminate the parasitic loss of the coolant flow.
Nuclear heat is cheap enough that it may not make sense to push the performance too hard. What you want is low cost, and reliability is going to be better for that than thermal efficiency.
Nuclear heat is cheap enough that it may not make sense to push the performance too hard. What you want is low cost, and reliability is going to be better for that than thermal efficiency.
Now you’re talking. Those are exactly the measures I am trying to maximize. GE has a line of turbo expanders for process heat systems that seem well suited for my needs – they are simple machines designed to operate at moderate temperatures using what would otherwise be wasted heat.
The answer is: a cascade of centrifuges, the production rate is higher than your UF6 enricher working for your Adams Engine, cost is lower than the UF6 enricher, fewer are needed than you need UF6 enrichers. Cost is lower too. The reasons for this are stated earlier: it’s cheaper, more available, nonradioactive, nontoxic, nonproliferative, has a larger mass difference versus U235/238, operates at lower temperatures, is always a gas never a solid, etc. etc.
I don’t quite understand why you think uranium enrichment is perfectly fine (in fact your design needs more enrichment per kWh than a large LWR) but nitrogen enrichment, which is far easier in every single aspect, must be carefully considered.
@Cyril R
I think uranium enrichment is just fine because it is already a commercial process in which someone else has made the capital investment required to supply the market. The nitrogen enrichment that you are suggesting is not a commercial product and has no other potential customers other than my little Adams Engines. In other words, you are suggesting that we take on an uncertain additional capital investment plus an uncertain additional operating cost in order to continuously supply make up coolant and coolant for new engines.
A fundamental design goal of my project is to drive down capital costs – that is the “big noise” that has slowed nuclear energy proliferation around the world. Without a careful accounting of the costs and a reasonable effort to compare the added cost against the cost of taking the path that I have proposed of simply dealing with the C-14 that gets produced, it would be short sighted to assume that your proposal is cheaper.
Nuclear weapons proliferation is not a concern for me, especially with regard to enrichment plants located in countries that are already nuclear weapons states. It is an argument used by antinukes to add cost and schedule burden to nuclear energy projects in order to slow the real proliferation that worries most of them; for various reasons – either competitive or philosophical – they do not like the idea of abundant, cheap, emission-free power that can (and will) replace fossil fuels with superior performance on many measures of effectiveness.
Questions for both of you:
Cyril, most of your N-15 is going to be covalently bonded to N-14 atoms. How do you propose to re-sort it? Perhaps you’d be best advised to use ammonia instead of N2 until the final step of recombination to molecular nitrogen.
Again, how do you propose to capture it? The chemical combination of nitrogen with carbon is a gas. Oxygen and carbon, also gases. It doesn’t lend itself to easy separation. Alkalai metals have the virtue of being highly reactive and forming solid products.
Good point, we need another step. First the centrifuge train does bulk seperation, producing a stream of N2 enriched in N-14-N15 and N15-N-15 pairs. The next step is conversion of of the preseperated enriched nitrogen gas to nitrogen monoxide (NO) and put that through the cascade for final enrichment.
My point wasn’t judgmental, it was simply an observation. Fissile material will be subject to regulations not subject to nitrogen. That’s a fact of life. We can work to make the regulations more reasonable, but fissile enrichment will always be burdened with many more regulations than the simple safe nontoxic noncritical nitrogen enrichment.
I should also point out, that your design needs a higher enrichment than a LWR. Thus it is not as available and marketed as you’d like. You need higher enrichment, so you will have a specialized, additional need that the current market doesn’t have in quantity (only minor special orders of up to 20% enrichment for research and isotope production reactors).
The mass-delta between (N-14)O and (N-15)O is 3.3%. The mass-delta between (N-14)H3 and (N-15)H3 is 5.9%. Furthermore, ammonia is a bulk commodity. You would probably be better off enriching ammonia from an existing production facility and returning the (N-14)H3 to the fertilizer/chemical market than building something new to make NO.
On the other hand, you can already buy neon off the shelf.
I’m sorry, but that’s nonsense. The CO2 dissociation temperature is >>1000 degrees Celsius. CO2 is slightly oxidising at elevated temperatures; perhaps this is what is intended. But there are excellent modern materials that can take it, such as Inconel 718 and silicon carbide, by forming protective oxide layers.
One thing with CO2 is that it oxidises graphite: CO2 + C = 2CO. This is obviously a problem for graphite TRISO fuel. But not with a thick silicon carbide barrier on the graphite surface. Which may be needed anyway, to avoid air or water ingress oxidising the graphite in an accident or off normal event.
NGNP seems to focus mostly on superheated steam as the secondary fluid (working fluid) with the primary coolant being helium. This is probably because of the difficulty of developing helium turbines and related machinery. Steam cycles are off the shelf, with many large vendors selling proven equipment. But if you’re going for a steam cycle, then there’s the potential for a leak into the helium loop; superheated steam cycles operate at higher pressures than the helium primary loop. So you want those silicon carbide coatings anyway.
Helium leaks are not a problem. The stuff is quite affordable. We can afford to lose 100% of the inventory per year. Helium can even be extracted from the air if there’s a shortage. But CO2 is pretty attractive, too. In most ways it’s much more proven than helium, with a good deal of Britain being powered via this gas, as mentioned.
A helium cycle would be much more attractive if it were a direct cycle, ie if helium turbines were already developed. But this is true for CO2 as well; supercritical CO2 cycles are very impressive, perhaps more so than helium Brayton cycles.
I still prefer molten salt coolant. It is well known that maintenance at high temperature is an issue, though many systems have been developed to aid here. ORNL’s molten salt reactor experiment managed to effectively do all sorts of maintenance and inspection using primitive 1960s remote manipulation technology. With today’s robotics, advanced manipulators, it’s not such a big deal anymore. I would encourage anyone a visit to an iron/steel fabrication facility. Huge pots of molten iron at 1600 degrees Celsius. The more modern facilities have some impressive robotics and manipulators.
Nuclear reactors of any type require a good deal of remote manipulation. A gas cooled reactor can be cooled down to room temperature, but that doesn’t mean workers can casually stroll into a 10000 mSv/h environment. Replacing core internals in any reactor, is a remote maintenance job by definition.
If there’s a shortage of helium and your most economic source is the atmosphere (5.2 ppm), you’re back to neon (18.5 ppm).
Helium is currently priced far below replacement cost due to the insane US government policy of selling off the strategic helium reserve on a set timetable. When it’s gone, look for lots of things to get far more expensive.
Helium and neon are both extracted from the atmosphere. Neon from the atmosphere is the only source of neon we’ve got, and since it’s the before last gas to condense, recovering it means you also get helium as a given (it’s all that’s left in the condensate after neon).
Helium from natural gas wells is cheap. But helium and neon from the atmosphere are perfectly affordable. It’s a fairly marginal cost for a nuclear plant, so we can afford to pay 10x as much easily.
France’s CEA, in a monograph published in 2006, estimated that 5% of the world’s current helium resources would be sufficient to supply a world fleet of helium-cooled reactors with twice the capacity of the world’s current fleet of reactors. I doubt that we’re going to build that many helium-cooled reactors, but this does illustrate that getting helium to use as a coolant is not a serious problem.
Rod,
Why Triso? The German test reactor had them was gas cooled but wasn’t a success.
They even used thorium fuel cycle.
Now plans are for salt cooled with Triso fuel, that could solve the problem the German rector had.
Salt is easy to drain from the reactor the experimental msr in Oake Ridge, was shut down every Friday, and started again Monday.
What I have been read Alvin Wienberg could get physical contact whit inside the reactor as son as 4hour after full power.
Sandia National Laboratories has been using super critical CO2 and closed Brayton cycle some years (as I´m shore you know) in a 10MW test turbine.
So what is the benefit with graphite pebbles with nuclear fuel in?
I can only see how it will be more expensive compere to liquid fuel, you can have empty graphite pebbles for slowing neutrons in a MSR and then get rid of the problem changing tons of graphite every forth year (or 30th if Fuji was right).
Liquid fuel and fluoride salt must have the biggest potential, first maybe with fast spectrum and no chemical processing, just ad fluoridated U, TH PU and all other trans uranium, the fission products will get of as gasses, that can be stored until back ground radiation.
MOSART is a way with slow spectrum and graphite, but fast spectrum can be smarter thought you don´t have to remove Protactinium in the Thorium cycle.
That fast reactors needs 10 times more star up fuel, is bad for humanity, but not for US, Sweden, Germany, Finland and all other county that have nuclear wast with big funds for put the wast in ground in stead of destroying it and then release up to hundred times more useful energy. (that is one of the best argument for nuclear power that often reach anitnuks)
Sooner or later will all heavy nuclei fission or am I wrong?