Search results

  1. R

    Specifying temperatures in MCNP

    How about "Specifying temperatures in MCNP"?
  2. R

    Specifying temperatures in MCNP

    I also suggest that you change the name of the post to something that has to do with specifying temperatures in MCNP. Your question has nothing to do with supercritical water reactors.
  3. R

    Specifying temperatures in MCNP

    In the cell cards, you specify the temperature in units of MeV by multiplying the temperature in Kelvin by the Boltzmann constant 8.617e-11 MeV/K. For example, 600K would be "tmp=5.17020E-08" However, this is not the only place you need to worry about temperatures. In the material cards...
  4. R

    3D model of the VVER reactor

    That is really nice, a lot of detail!
  5. R

    Neutron quantity normalization in an eigenvalue computation

    You are correct that it is an eigenvalue problem and the eigenvalue is k-eff. If you write the equation in matrix form ($Ax=\lambda x$) you can see that the magnitude of the flux ($x$) is arbitrary. You can multiply the flux by any non-zero value, and it will still be a valid solution to the...
  6. R

    I want to know how I can plot Nuclear reaction rates when the equation depends on the fusion cross section of the reaction

    I just realized my last post was incorrect, and I don't see a way to edit it. The cross sections are always going to be evaluated at "E", you should never have to divide by "delta-E". It is the flux that can be a function of E. Sorry for the confusion. Mentors: is there a way to edit my...
  7. R

    I want to know how I can plot Nuclear reaction rates when the equation depends on the fusion cross section of the reaction

    Do you have a plot of the cross sections, or a table of the cross section values? You will need the table of values. If you only have the plot, check the website again to see if there is a way to download the raw data. Next, check to see if the cross sections are evaluated at "E", are are...
  8. R

    First-Year Undergraduate Nuclear Fusion Advice for Experience?

    If you are really interested in fusion, mechanical engineering is not the right degree for you. You should consider switching to engineering physics, electrical engineering, or even physics. Prepare to go all the way with a PhD. As a freshmen, take as many math and physics courses that you...
  9. R

    Scaling nuclear reactors

    I think it might be easier if you describe exactly what equations you are trying to scale. Are you looking at the diffusion equations? 6-factor formulas? transport equations? something else? You ask about the number of scattering collisions to slow down a neutron, but this is never used as...
  10. R

    Inventory of Cs-137

    I just noticed that the original post was from 2011. I assume he eventually figured it out :)
  11. R

    MCNP model

    Are you asking what a spacer grid looks like? or setting up the geometry in MCNP? What work have you done so far?
  12. R

    Inventory of Cs-137

    You are on the right path. However, I don't know what the application is so I can't tell you if your assumptions are correct (is this a HW problem, or a real application?). Some things to think about 1. You are assuming a constant fission yield of Cs-137. This may be appropriate, but a...
  13. R

    MCNP summary table

    This table provides the "neutron balance" for the system. The left hand is all of the events that create a neutron and the right side is the events where the neutrons are lost. The main source of neutrons is prompt fission, with smaller contributions from delayed fission, (n,xn), and...
  14. R

    Result is zero flux for MCNP6 *F4 tally

    Then the warning is correct. You only have a vacuum, so the code is giving you a warning that there are no materials (or cross sections). The code is very general and models a lot of different physics, so there is a fairly steep learning curve to it. However, I would not say that it isn't...
  15. R

    Result is zero flux for MCNP6 *F4 tally

    You do not have any materials defined. Each cell should have a material number as the second number, but all of your cells are void (material 0). No materials, no cross sections.
  16. R

    Computer simulation of MSR work

    Sounds like a fun project! To model a reactor, there are several different "physics" going on in the core. 1. Thermal hydraulic model of the molten salt core - This can be as complicated as CFD, or as simple as a heat balance equation. 2. Thermal hydraulic model of the steam generator and...
  17. R

    Analytical solution to mono-group kinetics with a ramp of reactivity

    I don't think this is correct. The prompt jump assumes the precursors are constant, not the power. Physically, you are looking for the change in power after a step reactivity change. The prompt neutron population starts to increase/decrease almost instantaneously, but it takes a while for the...
  18. R

    Analytical solution to mono-group kinetics with a ramp of reactivity

    The prompt jump approximation *is* to assume that the precursor population doesn't change, so I'm not sure what the difference is between your 1st method and 2nd method. Aren't both methods considered prompt jump methods? Irregardless, let's take a look at your math. You stated that the...
  19. R

    Structural Mechanics in Reactor Technology (SMiRT)

    I'm replying to an old post, but SMiRT-25 will be held in Charlotte, NC on Aug 4-9, 2019.
  20. R

    Nuclear Fuel Rods & Fission

    Most of the energy (~82%) from a fission becomes kinetic energy of the fission products, which causes the fuel to heat up. The heat in the fuel is conducted through the fuel, through the clad, and into the coolant. Fission product decay produces an additional amount of energy (~7.3%) that is...
  21. R

    Reactor dynamics with a large reactivity insert

    You are right, it can get complicated quickly. It's hard to give more advice unless I know exactly what you are trying to solve. Here is a paper that analytically solves the point kinetics equations with adiatic feedback. It can be done, but it is probably more complicated than a homework...
  22. R

    Reactor dynamics with a large reactivity insert

    You need to use the point kinetics equations to solve a step insertion transient (at a minimum, you could also use 3D kinetics). So how do you do this? 1. Solve it numerically. It is pretty easy to solve by writing a simple computer program. There are built-in solvers in Matlab, or you can...
  23. R

    Resonance escape probability after a change in temperature

    If I understand your question correctly, are you asking if resonance absorption higher in a heterogeneous system? The answer is no, resonance absorption will be higher in a homogeneous system. Consider the case of the first "pile" reactor in Chicago which had uranium slugs arranged in a...
  24. R

    When can I use the prompt jump approximation?

    When you derive the prompt jump, the first approximation is that the precursor concentration does not change and you are calculating the change due to prompt neutrons. This is a valid approximation for times immediately after a transient because the prompt neutrons have a much shorter lifetime...
  25. R

    Chernobyl HBO Chernobyl physics questions

    You are asking good questions... > 1. He says water reduces reactivity but steam increases it. How does this really work? You're first sentence is really saying the same thing. In the case of the Chernobyl reactors, water acts as a neutron absorber. if you add more water, you absorb more...
  26. R

    To use Genpmaxs for PARCS XS generation

    I can't answer your question directly, but the link you gave points to the old Purdue site. You may want to look at the new site at Michigan: There is an e-mail on the webpage to send support questions.
  27. R

    Resonance escape probability after a change in temperature

    Oops - I had the wrong sign in my previous post. Corrected above. (Is there a way to edit my earlier post?)
  28. R

    Resonance escape probability after a change in temperature

    I'll try a little different approach... With Doppler broadening, the *peak* resonance cross section decreases, but the width of the resonance increases. The net effect is that the total number of absorption's increases, so the *average* cross section increases. There is a "self-shielding...
  29. R

    Adjoint Diffusion Equation

    It is a little harder for me to dig through because you've separated the inelastic and elastic, and assume downscatter can only occur over one group. Many of the terms on the LHS are commonly grouped together as a "removal" cross section. From Hebert, "Applied Reactor Physics": Multigroup...
  30. R

    Neutron's crow flight distance & 2° moment of a distribution

    I don't think r^2 is the "crow flight distance". Are you referring to the older Lamarsh book? (This is the only nuclear engineering book that I know of that has crow flight distance). He talks about the crow flight distance, but he uses r^2 because it is a quantity that is part of the "fermi...