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  1. I’m pretty sure that the mPower design is older than the NuScale design, at least in concept. The mPower reactor is based on a design for a maritime reactor that was developed by Babcock and Wilcox many years ago. Recall that B&W built the reactor for the NS Savannah.

  2. Interesting article, Adams. TVA has been jerking the public around, about 8 million people, for a very long time. Its huge unsustainable debt makes it impossible to play any kind of free-market role (it does mess up the market though) in the planning, construction and operation of nuclear reactors. And that is because the TVA IS the federal government. Other than loan guarantees which make things a bit less risky as a business undertaking, the federal government should not warp or squelch the entrepreneurial spirit of the electrical energy industry. And that the TVA does. Ironically, the federal government explicitly does not back up TVA’s indebtedness.
    TVA is a strange animal and I’ve written quite a lot about it. See my site , bottom of left column for my latest.
    Ernest Norsworthy

  3. Brian – I have a technical manual in my library from the NS Savannah. There are enough major differences between the mPower and the NS Savannah, which had external coolant pumps, pressurizer, external steam generators, etc. that it is not fair to give that plant credit as establishing precedent. There is no doubt that B&W has a much longer history in light water reactors than NuScale, but I am pretty certain from good sources that they were not thinking much about commercializing any modular light water reactors as late as three years ago. In fact, I think I can point to the exact date when the thought started swirling again after a lengthy period of dormancy. If my guess is correct, I was actually in the room when that happened.

    1. Rod – Oh no, I’m not saying that mPower is a copy of the NS Savannah’s reactor. No, mPower is essentially a design that B&W was working on well after the Savannah was taken out of service.
      I’m getting this information from people who actually worked on this design back in the day and from a presentation that I saw, which given by the CEO of B&W Modular Nuclear Energy, LLC.
      At one time, B&W was thinking about commercializing modular light water reactors for maritime applications, and they had done a significant amount of work on the design. Market conditions changed, however, and the ideas were shelved. When small reactors began to become a hot topic again, they dusted off the old designs and … voila … mPower was born.
      You don’t think that B&W simply pulled this design out of thin air in such a short period of time, do you?

      1. Brian – I do not think we are disagreeing at all. The mPower is most definitely an idea that has been swirling around B&W for many years. What I am trying to say is that there was no active project within the company to pursue any of their shelved designs up until about three years ago. They had some internal discussions going about how they might reenter the commercial nuclear market but had not really seriously considered going small. The company that has just recently begun using the B&W name again – they operated for a long time under the name of BWXT – is actually just a portion of what used to be B&W. The commercial arm that built reactors like TMI was sold off to Framatome back in the 1990s, but there was a national security reason for splitting the company and keeping part of it operating under US based ownership.
        The mPower design has been refined quite a bit in the past few years, but it was a design that had a long history before it got put on the shelf and languished for well over a decade.
        Your phrasing “when small reactors began to become a hot topic again” is interesting to me. I prefer NOT to use the passive voice, but will refrain from assigning credit for that decision.

        1. Oops – time flies when you are old. Looks like the actual date was Jan 23, 2006, which was 4 years ago, not three.

        2. Rod – I don’t think that we disagree either.
          My phrasing was deliberate, particularly the word “again.” The nuclear community is not immune to fads and fashion, and the concept of modular reactors has been popular in research circles before. I, for one, hope that the current interest in small, modular reactors is not just another passing fad.

      2. So, if one was to look at the design docs from the Savannah, one could get a pretty decent idea of how the mPower works?
        I wish there were more publicly accessible docs (or at least docs available) that I could cite to do basic articles on the mPower like I did for the Hyperion module. B&W appears to be playing their cards very close to their chest – even NuScale has more stuff about what’s going on.
        This diagram is especially interesting.
        B&W’s docs say that it uses PWR fuel…but they don’t say it’s a PWR… I can see from the diagrams that doesn’t have circulation pumps, at least non-integral circulation pumps, and as far as I know, it appears that there are several steam generation loops. Or more precisely, there’s a short preheating HX loop near TAF on the exterior of the reactor, and then what I think is a superheating loop above the preheating loop. Also, the RPV is way, way too long for it to be a pure PWR. PWR RPVs are short and squat, or at least those that I know of are. Those dark blue thingamabobs between the lower loop and the upper loop seem to either be steam dryers? Or maybe they’re pumps? Further, could the exterior flow of the upper of the RPV come from the interior flow of the lower RPV? And the exterior part of the lower RPV – which has the preheating loop – could it be connected to the interior part of the upper RPV? That would explain the blue parts. They would be steam dryers? And the middle section would be a flow-diverting manifold or plenum or something like that?
        I have a feeling that something weird is going on here in the design that might be interesting.
        I can think of several possibilities:
        1. The mPower has an integral steam generator in the RPV, therefore steam comes (indirectly) out of the RPV;
        2. it has boiling in the RPV, and is thus an indirect cycle BWR – but why would anyone allow primary boiling…wait…if you were to have an integral primary, it just might behoove you to allow primary boiling just to get rid of LOC modalities and work with much higher pressures and temperatures in the RPV, as the RPV is a stronger, integral unit? Plus, if boiling is allowed, this would provide for circulation within the reactor.
        3. it is a combination of 1 and 2;
        4. it generates supercritical steam?
        Or perhaps it’s something else that’s entirely wacky, and maybe I should go to bed?

        1. Another possible rationale for allowing boiling within the primary – coolant circulation speed directly correlates with reactor power in BWRs. As void clearance rates go up, power increases. This allows BWRs to be controlled from 30% to 100% of power without moving control rods. This gives one of the major advantages of BWRs – the ability to use a deionized water chemistry and thus avoid the use of borated neutron absorber to control reactivity. Avoiding use of borated neutron absorber is a good thing, as it lowers corrosion concerns.

          1. Dave – I had a chat with Michael Shepherd of B&W at the Platts Nuclear Energy meeting and listened to his presentation. As a bit of background, Mike has recently come to B&W from GE, where he spent a career working on BWR’s.
            The mPower is a system designed by people who have taken lessons and concepts from both branches of the LWR family. It does not have a pressurizer, pressure is controlled by maintaining a steam bubble at the top of the pressure vessel. It does not use dissolved boric acid for reactivity control. It does use circulation pumps at power, but has sufficient natural circulation flow to remove decay heat. The steam supply system is all contained in the single vessel – there are integral steam generators where feed water comes in and steam goes out. There is a small amount of superheat in the steam. The fuel assemblies are standard PWR type fuel, only shorter. (6 feet in length.) There is a flanged connection that allows the top of the system to be lifted off during the refueling event that is necessary every 5 years. There is no designed fuel shuffle, the entire core is replaced and set aside inside the containment. Same burn-up limits as a standard PWR. Enough space is provided for 60 years worth of used fuel storage.
            The integral NSSS eliminates the piping break LOCA potential. (This is the same with the NuScale, by the way.)
            There is some amount of load following capability, but the best economics come in a base load mode. (That question was asked and answered during the session.)

  4. Aside: it isn’t that frustrating when debating types like Romm or Lovins. You can have a certain amount of fun calling them on their planet killing BS. They aren’t sincerely debating a position and its time to dismiss them to their faces. They say climate change is the problem civilization faces, yet they want to stand in the way of ongoing operation and future expansion of what the authorities they say they recognize, for instance the IPCC, says is a low carbon baseload power source equal to solar or wind when it comes to emissions. They say MIT are the experts yet MIT directly contradicts what they say about how expensive nuclear is, and the cost of new nuclear is their #1 debating point. Their arguments are of such low quality they can be told they aren’t serious. Given that they say the climate situation is so dire, someone advocating an expansion of nuclear can tell them to come up with a better explanation of their case or tell them they should get out of the way. End of aside.

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