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  1. Some other considerations:

    There are limited sites with access to bodies of water to serve as heat sinks as well as water supplies for cooling towers. This puts a premium on thermodynamic efficiency.

    There will be periods of time where NG will be inexpensive enough that nuclear will be temporarily uncompetitive. Yet nuclear must maintain a highly competent but expensive staff regardless of whether the plant is producing any power. The expense of maintaining a large staff for an uncertain period of time was a significant factor in closing San Onofre.

    Plant operation should be automated to the maximum practical extent. This includes reactor operators. As someone who’s career in nuclear power was heavily involved with simulators it pains me to say that if a proposed plant design retains the model of overwhelming reliance humans being repeatedly trained in simulators for every casualty, your design needs to be reconsidered.

    The Burger King approach of “Have it your way” and allowing the utilities of wide ranging competencies to modify designs or request changes has to stop.

    The day to day routine maintenance function are best handled by on site staff. Beyond this, the remainder would best be provided by a service contract with the vendor. Even the on site people could be vendor employees. This distributes training and personnel costs over a wider base and makes smaller reactors feasible for smaller entities such as municipal utilities or manufacturing interests.

    1. You could reduce operating cost/MWe by building 8-12, 1 GWe nuclear plants at o e site, like Canada and China do along the coast of the ocean or large capacity lakes, all the same, shared services, one permanent refueling team, c ok moon parts Lower per plant inventories.

      1. Attn: Robert Hargraves and Ed Pheil

        In light of TransAtomic’s [not so] surprising announcement that it is ceasing ‘operations’, no doubt partially due to their claims not holding up to peer review, I pose the following question to Ed Pheil and Robert Hargraves, who are MSR proponents (Elysium and ThorCon respectively):

        Knowing that the Elysium proposal is a fast reactor…

        Why have I not seen discussion of moderating MSRs with double-walled water tubes instead of a graphite (or in TransAtomic’s case – hydride) core structure? Presumably, a design could employ circulation of water in those tubes at low pressure (atmospheric) so long as a gas gap or evacuated annulus insulated the moderating channels from convection (neutron and photon heating alone). This would be similar to the CANDU geometry, but inverted so the calandria is a flowing fueled region and the pressure tubes are unpressured moderating channels. You could expect +97% of the fission energy to be deposited in the salt (inferred from knowledge of LWR fuel).

        Using liquid water also makes possible several trustworthy reactivity control mechanisms. For instance, if you control the inlet subcooling of the moderating channels you would have a strong reactivity ‘knob’ in varying their void fraction (like BWR). If you were to keep the water in the tubes solid, then you could dissolve boron in the moderator (like BWR). These different tacks would each you to load and suppress excess reactivity, change power level, and provide shutdown margin. Start-up in a boiling channel core could begin with dry moderator channels which are gradually flooded in order to traverse source/intermediate/low power range. Start-up in a subcooled solid water channel core would be a simple boron dilution. Major ‘selling points’ for MSR are high temperature (i.e. > 800C) and low pressure (near atmospheric) – so I couldn’t suggest something that would defeat those selling points.

      2. Nothing moderates like hydrogen and nothing packs hydrogen like water. On average a neutron loses half of its kinetic energy per collision with hydrogen. It is a flat probability curve; I’m sure that you are familiar with it; the probability for an incident neutron to lose 90% energy in a collision is the same as the probability to lose 10% of its energy. Diffusion length is on the order of 3 cm in water vs. half a meter in carbon. Moderating with water will absolutely minimize (the limit) the diffusion length in MSR and allow a smaller system to be ‘thermal’ than possible with graphite. The outer tube would be something like thin-walled Hastalloy and the inner tube would be thin-walled zirconium alloy. The pressure across the tubes would be p*g*h; a couple of atmospheres at the most; the tubes could be thin walled and even triple walled with leak detection to reduce water-salt event probability.

        I would like to state that as a career nuclear engineer I am an opponent of MSR technology since MSRs do not contain the fission products in cladding and are therefore difficult to maintain and operate from a radiological safety perspective. I have secondary and tertiary arguments against them as well; in my opinion, solid clad fuels are the past, the present and the future.

  2. At least Kairos power wants to “co-fire” the natural gas combustion turbine with a radiator like was used for the MSRE. I love the idea of Brayton cycle using nuclear heat. Bearing lubrication is a major hurdle for “direct cycle” where reactor coolant passes through the core – the lube oil will soot-up the core and cement it together. High temperature magnetic bearings for a 10-ton rotor don’t exist outside the pages of General Atomics reports. The MAIN engineering problem is a materials problem: what material is going to allow 1000C+ average and 1200C+ hot spot surface temperature on your fuel element and not degrade/erode over the fuel’s years of residence time…. TRISO? Maybe, but TRISO seems like it will remain expensive! Sintered ceramic pellets are CHEAP; sift, press & heat. TRISO involves physical vapor deposition; they literally grow the graphite coating in a methane atmosphere at coal gasification temperatures.

    1. FHR, MIT wanted to do gas confirming, but do we know if Kairos kept that part? I heard there were some other changes, when they are left the university IRP DIE funded team.

    2. Before assuming lubrication is an issue, it might be worth doing some additional research and testing.

      As you’ve noted, GA papers are full of assumptions about magnetic bearings, but there are many reasons why I take GA papers with a large, probably unhealthy dose of salt.

      I’ve a different judgement about the cost trajectory for manufactured, coated particle, actinide fuels. The materials used are cheap and abundant. The vapor deposition process is ripe for scale and experience improvements.

      I’m pretty sure X-Energy agrees.

      1. GA is He, which has less mass, and less lift capacity, compared to N2. As Rod, says, N2 is sir, whose bearings DO work, as that is the most common form of power being installed today.

  3. Open and closed cycle gas brayton are two different machines, and costs. Natural gas turbines are open cycle. Any direct cycle nuclear gas turbine will be closed cycle, with a much lower pressure ratio, and huge recooperator heat exchangers added, and the added complexity is harder to balance/operate.

    What killed ML-1 was not the reactor, but immaturity of the closed cycle gas turbine. While I think a closed cycle gas turbine is perfectly viable, it is not just a simple switch to the gas turbine system.

    And has turbines, and TRISO fuel is expensive. Stick with the simpler fuel compacts.

    1. Ed

      You’re confusing the cycle mods needed or suggested for closed cycle helium turbines with those needed to simply close a Brayton cycle.

      The only real difference between closed and open cycles is that the “heat sink” part of the cycle is a large heat exchanger instead of the atmosphere.

      Helium adds several complexities, including special turbines, special compressors and real temptation to add additional heat exchangers like recuperators and intercoolers.

      Adams Engines uses N2 because its thermodynamic properties are essentially the same as air without the corrosion potential and activation issues of 20% O2.

      There is a small effect on reactivity and a minor activation issue because N14 has a moderate neutron cross section for an n-p reaction that results in C14.

      Though C14 has a long half-life, it is a commercially valuable isotope that produces a pure, low energy beta particle when it decays.

  4. Maximum thermal efficiency in a simple Brayton cycle tops out at less than 40%

    GE claims 44% for the LMS100 in simple-cycle operation, but that is certainly on a lower heating value basis.  On HHV it’s almost exactly 40%, though.

    It is unfortunate, but many people trained as nuclear engineers have only a dim understanding of the massive structures, systems and components required outside of the highly refined reactor cores that are their main area of responsibility.

    Perhaps they would be best served by studying the use of supercritical CO2 as a coolant and working fluid, because the machinery required to produce the same amount of power as an air-cycle gas turbine is positively minuscule by comparison (let alone a steam turbine).  At the critical point the density of CO2 is 0.4682, and that’s about what it is at the COLD end of the system.  Given the fluid and power densities involved, the major problem appears to be making the machinery strong enough.

    The other decision that can throw the door wide open on developing nuclear heated Brayton cycles for almost any conceivable energy application is selecting a working fluid that can take advantage of existing Brayton cycle machinery.

    NetPower is developing an Allam cycle plant which uses (mostly) sCO2 as its working fluid.  There may be a route forward on this for nuclear heat very soon.

    Designers should be cautioned to start slowly in this area, there are safety and simplicity benefits associated with using system pressures that are the same as those used in combustion gas turbines.

    Actually, I’d advise the opposite.  For a nitrogen turbine, the major thermodynamic factors are the base temperature and ratio of specific heats.  Notice that pressure is not one of them.  If you multiply the input gas density by 3 at the same temperature the only thing that’s going to change is the shaft torque (power); all the stage temperatures should stay about the same.  This happens in reverse in aircraft; the shaft speeds and pressure ratios stay about the same, but the air density (and mass flow) drop radically with increasing altitude.

    If you need to change output power, running the system pressure up and down is an excellent way to do it.  The gas turbine itself won’t care much.

    1. @E-P

      Can you point me to the suppliers of supercritical CO2 machinery? I’d like to get some reliable quotes for cost estimating purposes. I’d also like to review operating experience, service support options, training programs for operators and maintainers, and warranty options.

      Before using system pressure changes as your method of power output control, I hope to take the time to move off of paper and test the response of real machinery to the variations in torque, blade forces, and other material stresses. I’m confident you’ll find that there is some margin available to use moderate pressure variation, but suspect that doubling or tripling pressure will either require substantial machinery alterations or will result in reliability challenges.

      1. Can you point me to the suppliers of supercritical CO2 machinery?

        Ask NetPower.  They’re either making it or getting it from someone.

        I’d like to get some reliable quotes for cost estimating purposes.

        Once they’ve got a few units in service that will be available.  It should only be a few years, and I know you’ve been waiting since the 80’s.

        I’d also like to review operating experience, service support options, training programs for operators and maintainers, and warranty options.

        It’s a little early to expect that yet, but given the glut of natural gas in NA and the demand for CO2 for EOR it can’t be too far off.

        The irony is that the fossil fuel industry will gift a fossil-killer power cycle to nuclear.

        I hope to take the time to move off of paper and test the response of real machinery to the variations in torque, blade forces, and other material stresses.

        You already have this in aircraft gas turbines, albeit decreasing from sea level as altitude increases.  All that’s necessary is to calculate the aerodynamic vs. centrifugal stresses and look to see when greater input gas density makes the former a significant factor to net loads.  Given typical turbine speeds I’ll bet it will be multiples of 1 bar.

        1. Actually, I’ve only been interested in nuclear gas turbines since the fall of 1991. Can’t quite date my interest back into the 1980s.

          Variation in atmospheric pressure for aircraft engines goes in the lower torque & stress direction. Pressurizing closed cycle gas turbines to produce higher power output from smaller machines goes in the opposite direction.

          There’s plenty of room for improved tech along the path I suggest, but the best way to produce the sustainable revenues that can provide revenues to pay for the R&D needed is to build what we can build today with the factories that already exist.

    2. With regards to marrying a turbine to a nuclear reactor, CO2 turbines in a direct cycle are not a particularly good fit. The reason being that CO2 tends to break down to Carbon Monoxide freeing oxygen when exposed to radiation inside the reactor core, a problem which gets worse as temperature and pressures rise. This creates oxidation issues in the core from both from the CO and free O. Higher the temperature and pressure the worse the problem. The AGR’s in the UK which use CO2 coolant manage this issue by a very complicated flow path (creating a very large expensive and low power density reactor) to keep the carbon moderator at temperatures around 300 degrees and only allowing the hottest CO2 to pass through the fuel assemblies which are conventional fuel pins with SS cladding to protect the cladding from corrosion. CO2 as a HTGR coolant is incompatible with a carbon moderator and fuel (BeO might be a possibility but its cost is prohibitive) and even when this is removed at high temperatures the corrosion problems are not insignificant.

      The other issue with CO2 turbines is their operating outlet pressure from the compressor is very high and would require a RPV in the direct cycle variant to withstand pressures higher than current PWR RPV. When coupled with a lower power density of a HTGR compared to a PWR and therefore larger diameter RPV the pressure vessel wall thickness would become very thick potentially making the RPV prohibitively expensive and very difficult to manufacture.

      The upside of CO2 turbines is they can offer similar efficiencies at around 550 C as you can get with a steam cycle but far more compact and simple. The potential is there to replace steam cycles on HTGRs that use intermediate heat exchangers and use CO2 turbines as a bottoming cycle on a HTGR with a direct coupled gas turbine. Either of the above options are available to any plant designer and would be dictated based on the economic competitiveness of the available technology and don’t greatly Impact the overall nuclear side of a HTGR design.

      1. Very positive, I have just started my PhD on a concept you might approve of 🙂

        The first stage in establishing N2 as a coolant and working fluid is to demonstrate the effect on core reactivity is sufficiently small that the changes in reactivity from pressurised to unpressurised are small enough to be counteracted by a small temperature rise coupled with a strong negative temperature coefficient (first part of my research). Once demonstrated then the possibility of utilising Nitrogen as a coolant and working fluid in a gas turbine can be explored.

        Nitrogen properties are such that it doesn’t readily react with other materials (although can cause nitriding of steels via diffusion this is limited to only the surface of the steel and therefore would only create a hard surface not affecting the bulk properties) therefore it’s not expected to present a material challenge at high temperatures, although it would need demonstrating in a strong radiation field (nitrogen is already used in autoclaves at high temperatures because it is generally unreactive).

        HTGR and coolant choices have unfortunately been driven by early rational decisions. in the 1950’s when most of these concepts were being considered gas turbines were still in their infancy, nobody considered a helium turbine being anymore of a challenge than a nitrogen turbine and therefore considering the superior neutronic properties of helium and on paper superior thermodynamic cycle properties helium made perfect sense. Unfortunately the view was then created that a HTGR is cooled with helium and very little further thought was considered to coolant options even when the practicalities of helium turbomachinery and the availability of conventional gas turbines became apparent.

      2. I like it better because it can reform in only one way with a mono-element. Sure there is some nitidimg, but not as bad as having nitrogen, oxygen, methane, and water as in a normal open air gas turbine. Much simpler by comparison.

      3. New claddings like SiC pretty much eliminate issues with nitriding and oxidation under sane conditions.  This lets you pick your coolant for its other properties.

        Question for anyone with expertise in the field:

        What’s the net effect of CO2 on reactivity?  Does the (n,p) cross-section of oxygen give CO2 more negative reactivity coefficient than the moderating effect of the carbon?

  5. Not the topic but now California is presumably committed to 100% clean energy. That ought to mean for transportation, space heating and electrical power. Ok, so everything becomes electric. A reasonable estimate is that California will need to somewhat more than triple electricity generation, assuming this is just moonbeams.

    So maybe Californians will swallow hard and accept some new nuclear power plants to meet this ambitious goal.

    Maybe New York is going to do the same?

    I’ll be so bold as to suggest a three stage design with a molten salt thermal store in the middle. The reactor working fluid stays in the reactor passing heat through an integral heat exchanger. That should make the NRC happy, well, happier anyway. The thermal store feeds enough heat through an exchanger for the load following generator, possibly a CCGT based on what I read in this article.

    But please feel free to tell me that is just more moonbeams; it has been that sort of week already.

    1. GA is He, which has less mass, and less lift capacity, compared to N2. As Rod, says, N2 is sir, whose bearings DO work, as that is the most common form of power being installed today.

      1. The big deal with helium (and all noble gases) is that the ratio of specific heats (γ) is much higher than N2/air:  5/3 vs. 7/5.

        The istentropic gas equation is Pv^γ = C.  Given that Pv = RT still holds, this yields:

        RT v^(γ-1) = C

        T = C/(R v^(γ-1))

        T goes up much more quickly when γ-1 is 2/3 than when it’s 2/5.  This means you need intercoolers between compressor stages to get a high pressure ratio with noble gases.

        The beauty of sCO2 is that γ gets close to unity at the critical point, and there is very little temperature increase in compression.  This radically decreases the energy input in the compressor and thus the back-work.

    2. California has either a law or state Constitutional amendment prohibiting any new nuclear power facility regardless of design until a permanent nuclear waste disposal option is available.

      My guess is that once the last nuclear power station is cold, dark and beyond resuscitation, a nuclear waste disposal option will suddenly become acceptable.

      1. Building a nuclear reactor in California that IS the nuclear waste repository solution, i.e., consumes the LWR waste like ElysiumIndustry.com, would therefore meet California requirements and be allowed to be built in California, right.

  6. He point being, N2 turbines have reliability and cost today, scCO2 is still far, far from that. You need high reliability to put it on a nuclear plant due to the high capital cost.

    1. I expect the Allam cycle to take off due to oil-field demands.  Restrictions on flaring will drive demand for something which can turn unshippable gas into exportable electricity, and the CO2 will find use immediately as a fracking fluid and also a miscible solvent for extracting oil that water cannot drive out of formations (see “fractional flow”).  The upshot is that there will be a LOT of Allam cycle machines in operation fairly quickly.

      With a large installed base, bugs in the system will be worked out at someone else’s expense.  All someone has to do is buy one (or a few) minus the oxygen plant and water condenser and put a nuclear heat source.

      I don’t think reliability is all that big of a deal.  The first-cut units are small, only 50 MW(e).  A reactor of substantial size would use several of them.  One could break down and the plant would still operate; you’d just isolate the failed machine with valves and fix it at leisure.

  7. To follow up on my earlier comment on need of s recooperator, the alternative to a recooperator is a steam rankine bottoming cycle to recover that bottom section of the T-S curve. That is what nat gas turbines do, combined cycle, and what FHR did even though they were lower temperature, bottoming cycle. FHR was 650C air working temperature, and not very economic as baseload plant with such a low temperature, the gas portion, as baseload, is hard to justify for such a low dT on the gas system, even with a combined cycle, so they had to add gas confirming to add economics.

    Indeed, Elysium is considering either an N2 gas turbine at 700C initially, fuel at salt 750C. dT 700-550 = 150C for an open air cycle. But, the goal is to hit 950C power/process heat cycle, dT=350C, 1000C fuel salt. N2 has certain reactor advantages, and obvious power system advantages.

    I have future hope’s for SCCO2, but it is clearly not there yet on reliability and cost knowledge yet. ScCO2 is very complicated at the near liquid end.

    1. Hey, up towards the top of the thread I addressed a question to you and Ed Phiel regarding MSR moderation.

  8. “The other alternative is to use helium cooling for the reactor, but to add a gas to gas heat exchanger to move the heat into air or nitrogen so that conventional turbo machinery designed for combustion turbines can be used.”

    Isn’t that the design of the HTR-10 pebble bed reactor at Tshingua University? And the commercial plant on the coast?

    1. As s Rod said HTR PM 200 produces 565C Ultra Super Critica (USC) steam. 3 of them ganged together will replace the odern coal boiler to clean the air in China. Th hey DO plan to backfit them. But, on as go forward basis, I can’t see MSRs doing new USC plants. USC power systems are ultra super costly too, and are only justified in coal by fuel savings of higher efficiency, whereas nuclear, especially MSR has minimal effect l fuel costs, so can not s as very much to justify the cost of USC steam power plants. Hence looking at superheated steam or gas turbine with steam bottoming cycle.

      1. If ultra super critical steam plants were super expensive, how was China able to build them at a rate that approached 1/week for so long?

        Sure, there are some complexities and some material selections that are not the cheapest available, but once organizations fully learn how to build them, they are reproducible for competitive costs.

  9. Well – If you are going to dream about what to do with the gaseous heat from a high temperature reactor. Think outside the box just a little. Forget the turbine. Solve a few bugs in the works, use conventional combined cycle and get near 60% efficiency. Find some bauxite and sell aluminum to the world.


    Before you say anything, remember, “Man will never fly.”

    1. I’m confused by your comment. You said “forget the turbine” and then immediately recommended use of a conventional combined cycle.

      Turbines are part of both the gas and the steam cycles that are merged together to make combined cycles.

      The Adams Engine technology development road map certainly includes combined cycle plants in future iterations, but the FIRST one should be as simple as possible to allow iterative problem solving.

      1. I forget some time when I am communicating with technical types that I have to be very exact. Forget the first turbine.and use MHD. The second turbine (steam) will still be needed until we think of a better way to make use of the remainder of the waste heat. The MHD that replaces the first turbine has no moving parts. Per Wikipedia the combination of the MHD and conventional cycle can give (theoretically) up to 60 percent efficiency.

        Parts left out cost nothing and never need repair – paraphrased Charles F. Kettering quote.

        Maybe by the time the natural gas gets scarce we’ll have developed quirk free MHD.

      2. Eino, as I recall the coal-fired MHD systems still had issues with erosion of the electrodes under the conditions of extreme temperature and chemical characteristics of the gas and ash.  They never got to the point of being economic.

        Today we’re at 62+% efficiency with natural gas CCGT using (temporarily) cheaper fuel, and the Allam cycle plants are promising ~50% with zero emissions.  I’m not sure where MHD fits anymore.

      1. I am not following. Reactors might make 1000C, but CCGT goes up to 1300-1400C already. So, how do you see MHD as a gas turbine topping cycle?

      2. CCGT goes up to 1300-1400C already.

        MHD goes up as hot as you can get.  It would fit well with oxy-fuel combustion to get the highest possible temperature and thus best ionization.

        how do you see MHD as a gas turbine topping cycle?

        1. Feed compressor output plus fuel to MHD system (probably require separate compressors for oxygen and diluent streams).  Tap off maybe 30%.
        2. Dilute MHD exhaust stream to maximum turbine inlet temperature and feed through gas turbine.
        3. GT exhaust to HRSG.

        If you can get 30% off in the MHD stage your theoretical efficiency goes from 62% to maybe 72-74%.

        I personally am skeptical about the usefulness of MHD in this area.  SOFC seems to have much better prospects as a GT topping cycle.  If you can skim off 60% of the energy using a SOFC with an 800°C exhaust temperature, you should be able to just about idle the GT with zero or minimal co-firing of additional fuel.  You can then co-fire to run the TiT up to the rated maximum, which is 1380°C for the LMS100.

        Guesstimating 500°C compressor outlet temp for the LMS100, 800°C FCoT suggests an equivalent fuel burn to a straight 1250°C burner outlet temp (750°C gain).  You then have another 580°C of headroom before reaching TiT limits.  If the fluidic/mechanical efficiency is unchanged (it will take a hit) the efficiency figures look like this:

        750/1330 = 56.4% of fuel used in SOFC @ 60% efficiency = 33.8% net output from SOFC
        22.6% of total fuel heat exhausted by SOFC.
        43.6% of fuel after-fired into turbine, for total of 66.2% of total fuel energy input to turbine.
        44% turbine efficiency = 29.1% of fuel energy output as turbine work.

        Net efficiency about 63% before whatever you can grab using a HRSG and ST.  Figure about 74% overall in SOFC/CCGT operation.  If you can run higher temps in your SOFC you can do better, but this leads to materials problems and the push has been to get temperatures down to increase lifespan and get rid of exotic, expensive alloys and such.

      3. I was just speaking to the fact that if MHD became a thing with any future heat source for power generation, it would not replace Rankine or Brayton; instead it would be upstream. I wasn’t thinking of any particular application for MHD.

  10. I still think it wise to consider having a secondary loop between the reactor as heat supply and the generator as heat sink.

    Then one can further consider developing the secondary loop into a thermal store.

    1. Fine. But realize that heat exchangers and separate loops add cost and potential failure points.
      I’ll keep advocating for safe enough, far cheaper systems that simply need the right fuel.

      1. I am impressed by what the Moltex Energy website states about their stable salt fast neutron reactor design. I note that that design has a secondary loop.

      2. David,
        Moltex has fission products in both the chloride fuel salt and fluoride cooling salt, then a 3rd salt to isolate water from the fast core. That basically adds a loop relative to most MSRs.

      3. I do concur in general with keeping the number of heat exchanges down to a minimum although the cost is highly dependent on pressure differential and overall system pressure. Some of the reactor technologies that use atmospheric liquid coolant can afford more heat exchanges due to the high volumetric heat capacity fluid and small pressure differences keeping heat exchanger materials thin. this keeps the cost of the extra heat transfer step small enough that the benefits (TES for example) are worth having. This is especially the case for Moltex’s Reactor.

        For a Gas reactor heat exchanges are quite expensive as the coolants are pressurised driving up heat exchanger shell thicknesses, low volumetric heat transfer and often large pressure differentials between each working fluid.

    2. David, that idea is attractive, but it comes with costs:

      1.  Delta-T across the new heat exchangers cuts thermal efficiency, decreasing revenue.
      2.  Another pump or two to fail, more pipes to break, etc.
      3.  Extra capital cost.

      I keep leaning toward the idea of thermal and electric dump loads.  You’d have some lower-priority, interruptible load which takes heat, electricity or both.  You use it to consume excess system output and turn it into other revenue streams.  One obvious scheme is applying Frank Shu’s torrefaction process to municipal solid waste.  Converting MSW into clean pyrolysis gas and stable char would slash landfill costs several ways, not the least of which would be making the product instantly stable and eliminating any requirement for capturing the methane product of anaerobic breakdown after closure.

      1. Engineer-Poet, I would prefer not to call those “dump loads” for fear of offending the owners. 🙂

        However, I have yet to read of such being constructed. Decades ago in the USA about 43 pumped hydropower sstations were constructed to precisely consume the excess overnight power from the nuclear power plants so that the latter could run at constant setting. But in the current state of the grid none of the 4 proposed pumped hydro schemes here in the Pacific Northwest can receive financing.

      2. I would prefer not to call those “dump loads” for fear of offending the owners.

        It’s the preferred term of art; I doubt it offends anyone.  Processing material otherwise destined for landfill and removing ~70% of it from the MSW stream would make the process an anti-dump load, to coin a phrase.

        I have yet to read of such being constructed.

        Because they haven’t.  One of my favorite suggestions for Duane Arnold and Ft. Calhoun is to centralize fuel-ethanol processing at those sites and use nuclear steam to mash, distill and dehydrate the product with carbon-free heat.  Oddly, nobody but me seems to think this is a good idea.  With molten-salt reactors or HTGRs, torrefaction/pyrolysis with excess primary heat becomes possible.  The pyrolysis gas appears to be well-suited for partial conversion to methanol without further adjustment, with pumping of CH4 into the natural gas pipeline system and combustion of excess H2 in gas turbines for peaking.  Yet, somehow, this rather obvious waste-diversion and polygeneration scheme has no proponent.  It is a mystery.

        in the current state of the grid none of the 4 proposed pumped hydro schemes here in the Pacific Northwest can receive financing.

        IIUC, the PNW suffers (if that’s the word) from an excess of hydro and wind during the spring melt period when demand is close to minimum.  The PNW is also an area of large production of forestry byproducts.  Converting chipped logging slash into solids plus H2/CH4/CO/CO2 and thence into pipeline methane, methanol and ammonia for fertilizer with this excess energy might enable more of this energy to be put to productive use.

  11. World Nuclear News [wnn at world-nuclear dot org]

    “Transatomic Power, which had been developing a molten salt reactor with the ability to consume nuclear waste, has ceased operations. The Cambridge, Massachusetts-based company said it intends to open-source its intellectual property, making it available for any interested researchers, and is in discussions with the US Department of Energy Gateway for Accelerated Innovation in Nuclear initiative, which has previously made grants to the project, to ensure the work remains publicly accessible.”

  12. Engineer-Poet — Thank you for the reply. Your assessment of the Pacific Northwest in the spring is accurate.

    The dozen large forestry operations in the state of Washington have centralized wastes which are burned in the fall and winter, providing a steady aggrigate of about 600 MW at the time of year with low water flows and higher demand; every MW is valued. Despite the decent wholesale prices, the forestry operations lose money running their waste burners to produce some electrical power. But they lose less than other means of disposal.

  13. My PhD topic is very similar to the concept described Although the application is ship propulsion. An interesting addition to the concept is waste heat recovery and salt storage. The thermal salt storage tanks make a useful radiation shield for the reactor and decouple peak power output from peak reactor power.

    Also using a direct cycle gas reactor for powering ships has president in programmes in the US (search EBOR in google) and Germany. Apparently Rickover despite all his other attributes and successes in Nuclear power was not a fan and went out of his way to try and stop any projects in this direction. My guess is he saw any work in the early years which wasn’t developing PWR’s as diverting resource which was dearly needed at the time.

    1. Fascinating, Jeremy.

      A while back I did some research on the NuScale reactor as a prospect for container ships.  Curious fact:  the upgraded 60 MW NuScale unit is now sufficient to power an Emma Maersk-scale vessel with just 2 of them, and the 700 ton module weight is less than 1/3 of the 2300 tons of the RT-flex96C which currently powers them.  That, combined with the elimination of most of the fuel oil that would otherwise power the ship, should give a substantial increase in cargo tonnage while allowing the ship to cruise at 100% power while in open seas.

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