Welcome to European Tribune. It's gone a bit quiet around here these days, but it's still going.
Indeed, having a hidden agenda (like generating plutonium or other dual-purpose, incompatible uses) is not a good principle when building a utility-size reactor (not that the British didn't do very well with windscale either, talking about non sense like air-cooled graphite moderated, though it was a small and openly military-only installation).

Note that the german BWR has a separate secondary coolant loop to drive the generators. I believe US reactors would have that too.

PBR's seem convincing to me yes, for a number of reasons, like:
  • passively safe

  • modular plant with small power increment, fit small grids, or even non-grid use like chemical process heat generation

  • compact vessel, suits a mass-manufacture-and-lease-then-take-away model, including for shipping to developping countries

  • ability to adapt power output quickly, to match peak demand, or simply to complement irregular renewables just like hydro or gas does

  • plus, there was actually a running implentation for years at Julich, which actually makes it just as proven as the EPR

  • Of course, there is the story of the jammed pebble at Julich, plus the (often untold) detail of the pebble cooling facility at the output of the vessel, before sifting pebbles to loop back into the vessel or to dispose of, which is a big security/safety weakness, plus it spoils somewhat the compacity thing.

    by Pierre on Mon May 1st, 2006 at 03:52:30 AM EST
    [ Parent ]
    Thanks guys for all the detailed technical input.

    In the long run, we're all dead. John Maynard Keynes
    by Jerome a Paris (etg@eurotrib.com) on Mon May 1st, 2006 at 05:24:16 AM EST
    [ Parent ]
    Are you sarcastic for the nerds, Jerôme :-?
    BTW I'd still like to read your opinion on my post regarding the impact of GTL on the gas and oil markets, here...

    by Pierre on Mon May 1st, 2006 at 06:42:27 AM EST
    [ Parent ]
    I don't think it's sarcasm: Jerome is a reality-based banker.

    A society committed to the notion that government is always bad will have bad government. And it doesn't have to be that way. — Paul Krugman
    by Migeru (migeru at eurotrib dot com) on Mon May 1st, 2006 at 06:48:30 AM EST
    [ Parent ]
    No, it was honest appreciation!
    As to GTL, it's a topic I know too much about and decided I could not do a short reply, and did not then have time for a longer one...

    I actually wrote a diary on this a year ago: How to make gasoline from gas

    In the long run, we're all dead. John Maynard Keynes

    by Jerome a Paris (etg@eurotrib.com) on Mon May 1st, 2006 at 07:48:11 AM EST
    [ Parent ]
    Mixing military and civilian reactors is never a good thing. Our only somewhat nasty accident happened at the Ågesta heavy water reactor, which was probably a joint effort between the military and the civilians.

    Peak oil is not an energy crisis. It is a liquid fuel crisis.
    by Starvid on Mon May 1st, 2006 at 07:45:17 AM EST
    [ Parent ]

    I confirm that in a BWR, the steam goes directly from the core to the turbine, including on the latest Siemens design. Product brief here. Very nice for conversion efficiency and the pressure stress on the core vessel is lower than for a PWR (operation at 75 bar for SWR-1000 vs. 155 bars for EPR). The issue is of course that the turbine is slightly activated by the primary steam and that a breach in a fuel cladding is much more annoying than with a PWR. The fuel assembly is also more complex and the control rods cannot be placed in the fuel channels (risk of being pushed out by the steam) so it has to be installed on the sides of the assembly cans. BWR is a different trade-off than PWR. Gain some, lose some, the eternal story of engineering.

    I'm pretty skeptical of PBRs.

    I find the idea of making the fuel hard to reprocess very offensive. Wasting all that good plutonium and that excellent fertile U238, what a shame. Just to think of all that energy sends shivers down my spine :)

    More seriously, the graphite pebble casing makes the fuel very bulky and hard to dispose. Burial of anything but ultimate waste is not a valid option in my view and even then, it should be reversible (I'm not very happy about Finland). Separation to recover the spent fuel safely is a no-no as it would creates a lot of activated graphite waste in dust form (C14 is biologically nasty). May be PBMR promoters think it's a smart idea but IMHO, it's about the worst you can do for waste management.

    Same for the non-proliferation claim. It looks pretty bogus. The large number of elements makes inventory control difficult and theft easy. A proliferator can purloin pebbles a few at a time, and by crushing and milling, recover the spent fuel (and create lot of activated dust, as mentioned above, but a proliferator would not mind). If proliferation is really a concern, fully canned reactors seem a better option such as Livermore's SSTAR concept. See that for more details.

    I'm also non-plused by the safety claims. The passive safety by Doppler broadening against thermal runaways is fine and proven but ...

    - The PBMR design has no containment at all. Whaa ?!? Big conventional reactors are of course fully containted but they are not modular and not suitable for operation in poor countries. For a more honest comparison, let's take the SSTAR design. The SSTAR is not fully contained neither but it is at least buried, all vessel breaches are contained within a heavy concrete casing, the vessel is mechanically much, much sturdier than a PBMR tank and the core is isolated in the middle of a large mass of lead. The only area exposed to ambient air is the wall of the bottom of the core vessel for emergency cooling. It's very thick and built as a single piece forging with no breach. You gotta try really hard to expose the core.

    - I haven't seen anything convincing about cold air inrush in case of a rupture at the vessel at the inlet of the coolant compressor. The pebbles would be exposed to a very brutal thermal stress so how about cracking a pebble, exposing a highly ragged and dispersed section of carbon to air and have a nice little bonfire? I know that pyrolytic carbon doesn't catch fire just like that but I would really like to see serious experiments with pebbles that have gone through multiple loading-unloading cycles with all the accompanying mechanical stress.

    My preference for future design rather go to metal-cooled fast reactors and, longer term, to molten salts reactors with continuous fuel control.

    And with that comment, promised, I'm done with nuclear geekiness for the week :)
    by Francois in Paris on Mon May 1st, 2006 at 01:54:16 PM EST
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