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  1. I am surprised China is following the old script. They talk like the next HTGRs after HTR-PM would be larger. Small enough reactors CAN radiate off their decay heat. Not sure why they do not learn from history.

    1. @Robert Margolis

      Perhaps you know something I don’t. AFAIK, the Chinese HTR-PM reactor modules will not grow in size or significantly increase in thermal power output. Power plants using those modules may be larger, but only by using more reactor modules for each steam turbine.

      Larger steam turbines are already in production for coal units. HTR-PM modules produce the right kind of steam conditions.

  2. Excellent article about no clear data proving economy of scale. This should have been part of the planning a long time ago.

  3. A couple thoughts. Some decades ago when interest rates were above 10% and reactors were scaling up from 600 MWe to 1100 MWe, and taking many more years to construct, we did a calculations in an engineering economics class. If it takes several years longer to construct a larger reactor, and construction work in progress interest (CWIP) and allowance for funds used during construction (AFUDC) get captured and capitalized at the time of commercial operation, one can demonstrate that fixed charges actually increase with larger reactors! A second example is the scale up from the Yankee Rowe 185 MWe plant to AP1000. Both utilize(d) canned reactor coolant pumps. While Yankee did not need external cooling of the RCPs, AP1000 was found to need to add such to maintain reliability. Added complexity, added cost. I believe economy of scale can be reversed if one could mass produce small modular reactors in a factory much like natural gas combustion turbines now are.

    1. Brain dead management is the common thread.
      MBAs who have never actually stepped outside to smell the coffee. Sadly they are everywhere, in government as well as in industry.

  4. I have often wondered why the decay heat can’t be used to operate a steam turbine at low power during the period when heat still needs to be actively removed. If the turbine can’t be operated below about 5% then maybe a smaller turbine could used for the purpose. Would that be more expensive than the present method of dealing with decay heat?

    1. @Bill

      This is done; see RCIC (small) and HPCI (larger) for BWR. They use an impulse turbine called a ‘Terry Turbine’… turbines are exhausted to the suppression pool; pumps normally take suction from refueling water (RCIC) and suppression pool (HPCI). Some BWR use isolation condensers instead of RCIC (I think).

      RCIC=Core Isolation Cooling
      HPCI=Core Injection (small break LOCA)

      1. I really do subscribe to the “economies of scale” arguments with regards to reasonably large reactors of 500-1300 MWe, installed at multi-unit sites being more economical (albeit uninsurable) than smaller units (or worse, distributed micro-Rx). Perhaps this trend is like a ‘bathtub curve’ where the reactors become more expensive as they tend towards civil engineering megaprojects. I am surprised to learn that this certainty is contested. I appreciate the ‘factory made’ argument where SMR (or worse, distributed micro-Rx) hardware is cheaper to make, but their not going to be cheaper to operate – big picure. One comical example in my sandbox (not an opinion): NuScale WILL require 24x the core design/licensing effort of a large PWR, since 12 cores will be designed and licensed with existing Framatome methods for half the MWe of a 1200MWe Gen2 LWR. The core design of NuScale is not in any way easier to design (likely more challenging) than larger LWR – especially if an assembly must be discharged early due to grid or FM damage creating an asymmetry or energy shortfall… There is no hand-wavy method that allows NuScale cores to be licensed without this explicit due diligence. [It is my opinion that] it will not be cheaper to maintain 12 Rankine plants over lifetime… micro-Rx typically have a cash flow of tens to hundreds of dollars per hour – it is pretty clear that salary to output ratio shall make them fully uncompetitive, even in markets where electricity retails for $300/MWhr if the large LWR is uncompetitive in markets where electricity retails for $190/MWhr (PJM).

      2. One comical example in my sandbox (not an opinion): NuScale WILL require 24x the core design/licensing effort of a large PWR, since 12 cores will be designed and licensed with existing Framatome methods for half the MWe of a 1200MWe Gen2 LWR.

        I don’t understand why a core that will be identical for every unit will require more design / licensing effort. Can you help me understand this?

      3. @ michael scarangella
        I Know little about how much money, time or manpower was actually saved by the fact that Byron/Braidwood and Marble Hill, all identical Westinghouse AP1000 plants saved on NRC licensing, but Byron/Braidwood used this tactic again on their plant license extension. so it must have helped. This should be applicable for the Identical NuScale plants. and by Identical, I mean Identical. They all had a common Safety analysis and PSAR Preliminary Safety Analysis Report and FSAR- Final Safety Analysis Report (Marble Hill did not have an FSAR as they did not get an OL). Shortly before Marble Hill pulled the plug, they received an order to relocate TG lube oil(?) piping in the Turbine Building because Byron/Braidwood had moved this piping, and ALL plants had to be identical.

  5. A large problem of graphing costs is the attitude of the NRC toward the BOP (Balance of Plant) before the NRC most equipment other than the NSS (Nuclear Steam Supply System) and the absolute necessary equipment to cool down the plant were NOT within the bounds of the NRC review. With the establishment of the NRC, the ratchet wrench began. TMI-II cost twice as much as TMI-I, most of which was from NRC mandatates needed to obtain an operating license and the doubling in construction time due to these required modifications. Requirements to meet TMI Lesson Learned requirements added so many items to the “Nuclear Safety Related” classification that Rancho Seco had to add two more diesel generators, among millions of dollars of other changes. I seriously doubt that any of the latest licensed NPPs are a full order of magnitude safer than the very first NPP. For what end? How many thousand of years of total operation of US NPPs and no one has been killed or died from their operation.

    1. Rich:

      I believe it is important to recall the basis used to justify separating nuclear regulatory functions from nuclear energy development and promotion functions, which were initially both done by the Atomic Energy Commission.

      The 140 days worth of public hearings about the adequacy of the Emergency Core Cooling System in the early 1970s raised considerable doubts in the minds of both legislators and the general public.

      The ECCS controversy raised real issues that were EVENTUALLY resolved with very expensive testing, but a major cause of the controversy was a [somewhat legitimate] question about the scaling factors used as reactor power outputs doubled, doubled, doubled and doubled again. (60 MW, 120 MW, 240 MW, 480 MW, ~1000 MW)

      Here is one version of the history

  6. @David

    The cores are not identical, if they are not identical. The NuScale core will not be loaded and discharged as a unit – it will be shuffled. The design certification shows the reference design and planned shuffle scheme, with fuel being loaded for 3 cycles. The biggest variables that will yield varying and compounding divergence from the reference design are availability (did the unit trip or did it run well?) or WORSE, must any fuel assemblies be discharged prematurely due to damage (leaking?). Refueling outages are planned a cycle or [typically] more in advance and are fixed to begin on specific dates – assumptions are made about how the reactor will operate and fuel is bought to meet requirements given all those assumptions. There is typically ~20 EFPD of slop that can be accommodated for unplanned shut-downs before the planned falls outside of its licensing space. If the reactor has an unplanned shutdown, loading the fuel you’ve already procured will make the reactor more reactive, which will push MTC more positive – at some point it violates tech specs.

    So rather than assuming all the fuel in all the 12 modules will be at varying stages of the same trajectory – all covered by a single licensing analysis, you might want to imagine how the various cores might diverge, because that is what they will do. It will get really interesting with that 6-foot core when a damaged fuel assembly cannot be loaded for it’s 2nd cycle, there will be a tremendous radial tilt outside of anything we see in other PWRs.

  7. Interesting thoughts! I recently saw a lecture ( ) from the founder of The Energy Impact Center ( ) who believes the costs that accompany nuclear energy aren’t tied to utilizing or creating the energy source itself — they’re tied to the construction management aspect. Energy Impact Center recently launched OPEN100 ( ) to collaborate with professionals across relevant industries to provide a solution that builds nuclear power plants quickly and at a significantly decreased cost. I wonder if their final solution will involve a smaller plant.