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Numerical Nuclear Reactor

  1. Jun 17, 2006 #1

    Astronuc

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    This is a developing area in the nuclear industry involving large scale multiphysics computation.

    For the past several years Argonne National Laboratory and Purdue University have been supported by the Department of Energy (DOE) and the Electric Power Research Institute (EPRI) to develop a next generation nuclear reactor simulator based on the commercial Computational Fluid Dynamics (CFD) code STAR-CD to solve the temperature/fluid field and the integral transport code DeCART to solve the Boltzmann Equation for the neutron flux distribution in the reactor core. Applications of the Numerical Nuclear Reactor (NNR) to practical Light Water Reactor problems has required more than 100 million mesh and tens of hours of computational time on Linux clusters for the solution of a single reactor state point.

    Clearly computational efficiency must be improved. That will be quite a challenge.

    Some background on DeCART - http://www.inl.gov/scienceandtechnology/cams/d/high_end_computing_star_simon_lo.pdf

    Tom Downar is with PARCS (Purdue Advanced Reactor Core Simulator) which is part of the Purdue Nuclear Engineering program.
    https://engineering.purdue.edu/PARCS
     
    Last edited: Jun 17, 2006
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  3. Jun 17, 2006 #2

    PerennialII

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    ...... fashinating work they got going, and somehow get the feeling that they can actually pull through it, they may not be too greedy what comes to their goals & have an idea of the immense work ahead - but large scale multiscale is spreading. Got to taunt our guys with this if aren't aware of the project.
     
  4. Jun 17, 2006 #3

    Astronuc

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    Dave Weber from Argonne National Lab did a presentation this past Friday at a conference I was attending. I talked to him afterward, and he will be providing more information. I'd like to get more information from the PARC program.

    One aspect in which I'm particularly interested is the ability to properly calculate local asymmetries locally within assemblies (pin-to-pin) and grossly (e.g. octant or quadrant, or axial power tilts) within the core.

    Xe transients would be particularly interesting to model, as well as LOCA and RIA.
     
  5. Jun 19, 2006 #4
    Thanks for link, I did some undergrad work for Dr. Downar (great guy and very good prof) back in the late 80s (Integral Fast Reactor, Depletion Perturbation Theory) and it was good to see what they are up to.
     
  6. Jun 19, 2006 #5

    Astronuc

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    Validation of coupled thermal-hydraulic and neutronics codes in international co-operation (pdf, so use 'save target as' if bandwidth limited)

    Abstract:
     
  7. Jul 9, 2006 #6
    respected sir,
    i want some details related to nuclear reactor modeling aspects....i will be thankfu lto u , if u guide me in the same...if possible send me good links realted to nuclear reactor modelling aspects...
     
  8. Jul 10, 2006 #7

    Morbius

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    Astronuc,

    Programs are currently in the planning phases for the Dept. of Energy to conduct, under
    the auspices of the "Global Nuclear Energy Partnership" GNEP;

    http://www.gnep.energy.gov/

    an initiative similar to the "Advanced Simulation and Computing" ASC program that has
    for the past decade been very successful in increasing the computational capabilities
    for the Dept. of Energy's responsibilities for the stewardship of nuclear weapons in an
    era without nuclear testing:

    http://www.sandia.gov/NNSA/ASC/

    The ASC program has developed both advanced software, as well as hardware;
    resulting in the development of several advanced computing platforms:

    http://www.sandia.gov/NNSA/ASC/platforms.html

    including the world's most powerful computer, BlueGene/L at Lawrence Livermore
    National Laboratory:

    http://www.llnl.gov/asc/platforms/bluegenel/

    Dr. Gregory Greenman
    Physicist
     
  9. Jul 11, 2006 #8

    Clausius2

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    I don't truly know too much about this, but I can do imagine the kind of difficulty that the flow into a nuclear reactor has. I would like to know how much useful stuff do you get out of the simulations, I think you might be employing safety factors of order 1/2 or more. Solving the thermo-chemical-fluid problem seems unaffordable to me except if you run it on a Super Computer with full capacity and DNS codes. Solving it doing strong assumptions (as symmetry, steadiness, Continuum Flow, Equilibrium Flow, Chemical reduced mechanisms, Turbulence Models, decoupled wall Heat transfer and wall reactivity) is something more or less affordable (spending those tens of hours), but giving a lot of uncertaintity.

    I am particularly not prone to believe in large scale simulations unless they are done with DNS (currently unemployable in large systems). "Modelling the models", as I use to refer for instance to the turbulence models, is something good for engineering because it gives you a 50% less of uncertaintity, but not very interesting for science. I am kind of pesimistic with the actual state of the art of CFD employed in industry. I am sat in front of a door of a guy who does a lot of DNS in UCSD, in problems now applied to Oceanography, involving moderate large scales, but not employing the typical 100km-cell-size of the bulk simulations using LES or K-epsilon models that some people even in science unfortunately still do.
     
  10. Jul 11, 2006 #9

    Astronuc

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    That's why I am hoping to become more involved. We've had tentative discussion on coupling a thermo-mechanical code to this system :rolleyes:, which will be way more complicated. One of the biggest challenges is fluid-structure interaction (FSI).

    Proper benchmarking is the key. The gross uncertainties are not as large as one would think - it's something like bounded chaos. Locally at any given time, the uncertainties are larger - but on average are not so - such is the nature of turbulence.

    Thermocouples can be used to monitor temperature distributions and laser doppler anemometry can be used to monitor/measure the flow distribution. The integrated energy distribution can also be measured by subsequent post irradiation examination (PIE), part of which is the measurement of radioisotopic distribution.
     
  11. Jul 11, 2006 #10

    Morbius

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    Clausius,

    The hydrodynamic flow in a reactor is NO WHERE NEAR the complexity that would
    require a DNS code. We use DNS simulation to solve some of the problems in my
    field.

    Actually one can do surprising well with LES, K-epsilon, k-L.... models. It all depends
    on how much the hydrodynamics is affected by turbulence. For the Reynolds
    numbers one finds in a reactor - the answer is NOT MUCH.

    Doing DNS simulation on the coolant flow in a reactor would be "gilding a lilly".
    Dittus-Boelter analysis will suffice for reactor conditions.

    Dr. Gregory Greenman
    Physicist
     
    Last edited: Jul 11, 2006
  12. Jul 11, 2006 #11

    Clausius2

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    OOps sorry, I don't remember that discussion, but next time we will have it-:biggrin:

    Really? I must admit I'm having difficulties on believing in what you said. What kind of reactor are we talking about? Are you talking about a local (but very local) behavior of the flow? Are you guaranteeing me there is no single flow separation in the whole chamber? Have you ever simulated even the problem of the transversal flow over a periodic sequence of pipes? Is the Reynolds number so small to be laminar? I do NOT think so.

    Actually all the improvements of NASA and aeronautic companies on wing designs are in part due to the use of these models. The problem comes when used massively, without tunning the model coefficients, and moreover, when there is little o no capacity of interpreting correctly the results (and critically) by the engineer in charge.

    The hydrodynamics once the flow is turbulent and statistically steady is almost no affected by the Reynolds Number, BUT if the flow is not turbulent, the switch to turbulent DOES change its characteristic a lot, and in particular it DOES change the heat transfer dynamics, which turns out to be the most important thing in a rector right?.
     
  13. Jul 11, 2006 #12

    Astronuc

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    It's a very recent development.

    Flow in a reactor - in the core - is turbulent. Re is on the order of 400,000 in a PWR core.
     
  14. Jul 11, 2006 #13

    Morbius

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    Clausius2,

    Yes - I used to work in the field of nuclear reactor design. I am a computational
    physicist and that is EXACTLY what I have done - simulated the flow in reactors.

    As for your point about transversal flow over a sequence of periodic pipes; what
    direction do you think the coolant flows in a reactor?

    BIG difference between low density air at aircraft speeds and water flow in a reactor.

    If you are talking about an accident scenario wherein the hypothesis is that the
    reactor vessel has been emptied, and we are calculating the re-fill by the ECCS;
    then yes you have extremely turbulent conditions there.

    If you are talking about steady-state operation of the reactor; then NO - the reactor
    is designed so the flow is not turbulent to the degree to require DNS. The operator
    is also required to operate the reactor so that you don't have the drop in heat transfer
    that one would get with extreme turbulent flow.

    Dr. Gregory Greenman
    Physicist
     
    Last edited: Jul 11, 2006
  15. Jul 11, 2006 #14

    Clausius2

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    Please, do you mind giving me a reference for what you are saying?

    Or maybe we can work out the Reynolds number based on the fuel rod length (I don't care if it is a longitudinal flow), and work out if we have turbulen flow or not.

    And with all my respect, you are a computational physcist, but I am a mechanical engineer, and usually Fluid Mechanics IS NOT the area of expertise of a physicist. Maybe I haven't been doing simulation of reactors (because as I said massive simulations are useless for science if you do it employing the yet well known shortcuts).

    I still don't believe that stuff of laminar flow, and if you do some calculation or give me a reference I will be glad. Otherwise don't justify it saying that you have been doing that for a long time, because people also do wrong things for a long time in their jobs.
     
  16. Jul 11, 2006 #15

    Morbius

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    Clausius2,

    With all due respect; this IS my field - I am BOTH a Physicist and a Nuclear Engineer.

    This IS what I do - I write the computer programs that do this type of calculation.

    Then you don't understand how computational physics is done with reactors.
    You don't just do the calculation and be done with it. The calculations have to
    match EXPERIMENTS!!!

    All our calculation had to be benchmarked against actual experiments.

    These consisted both of small-scale experiments that simulated conditions in a
    reactor core, as well as experiments in test reactors.

    When calculating nuclear reactors, nobody lets you calculate using incorrect models.
    The assumption by the NRC is that your model doesn't work; and the burden of proof
    is on the designers / analysts to prove the models DO WORK.

    Dr. Gregory Greenman
    Physicist
     
    Last edited: Jul 11, 2006
  17. Jul 11, 2006 #16

    Clausius2

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    That's why I am asking you for a reference or calculation example. Give me order of magnitudes of the scales involved. It is pretty easy to figure it out.


    Small scale? I hope you/or the board of engineers are using dynamical similarity, because it is laminar flow, don't forget that. Otherwise you will be saying with your own words that the Reynolds number doesn't matter in this business, and that's only true when it is so large for assuming statistically steady flow and turbulent flow.

    This whole thread goes about until what extent these models work?. I'll put you an example. I know that some heat engine companies use codes for simulating the thermodynamic conditions in the combustion chamber. They are crowded with equations, every of them unidimensional (see the book of Heywood on this topic), giving you the maximum pressure, temperature of exhaust, pressure of exhaust, heat released, work done and all this bulk magnitudes. For sure it serves to the designer to have a first order of magnitude of the machine, and if you test it with an experimental model it does work for these purposes. But imagine I want to design the chamber or a intake valve, or the piston, or the exhaust pipe, do you think all those equations are useful for me? do you think that model is capturing the physics I need? Maybe Westinghouse is interested on knowing the bulk properties of your reactor, doing a lot of assumptions to obtain them, but you are not definitely capturing the physics for a detailed calculation, or at least this is my impression without knowing yet what kind of calculation you do.
     
  18. Jul 12, 2006 #17

    Morbius

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    Clausius2,

    You have absolutely no idea about the types of computer models that are use.

    They are not just filled with dimensionless correlations that somebody pulled out of the
    air. There's been LOTS of research by the national laboratories on validating these
    computer models so that reactor calculations are done only on CERTIFIED codes.

    Universities, national laboratories, in addition ot the manufacturers have all conducted
    experiments to certify these computer models. There is an entire body of knowledge.

    Perhaps you should check out "Nuclear Science Abstracts" to see the TONS of work
    that goes on to validate these models.

    Nobody licenses a reactor based on calculations using the type of computer model
    you gave with your combustion chamber example.

    Dr. Gregory Greenman
    Physicist
     
  19. Jul 12, 2006 #18

    Morbius

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    Then you can do it. I can't openly discuss design details on things that I've worked
    on.

    Dr. Gregory Greenman
    Physicist
     
  20. Jul 12, 2006 #19

    Clausius2

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    Ok, I will take a look at some of those abstracts.
     
    Last edited: Jul 12, 2006
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