Back to work on the same old. I figured out the grayscale images yesterday, but I still need to generate them for all the new uranium cases that don’t have thousands of kg of Hafnium in them. Additionally, I’m going to add a picture of the adjont source in the 1-D slab. Will need to try to make it eps. On it. Running the analytic oned solution now. I chose search and will see what we get. It’s been a while since I ran this code. OK I got a decent plot out. I used TeX text processing on it and it looks phenomenal. Now to generate the B&W ones for three cases…
In case 1, the 0-th timestep jump parameter is negative, so we need to switch the sense of all search directions. Run.py can handle that now, with the N option, for “negative.” That’s revision 8 in the itd svn repository. Rerunning v6 case with proper sense. Let’s see if we can do better. With improper searching, we started at peaking factor 1.05038 and got to 1.04 by bp search, and to 1.039 by end of BDT. Lame.
Uhh. I just spend 1.5 hours with MCNP crap for a student in my class. Why are we struggling with MCNP when we should be learning reactor analysis? Damn another hour with the class! These guys are killing me.
Well here’s some instructions I just made for doing safety analysis of SFRs in REBUS or MC**2:
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Disabling the criticality search in REBUS
by Nick Touran
If you want to perform any kind of basic void coefficient, Doppler coefficient, or temperature coefficient of reactivity estimations in REBUS for fast reactors, you have to disable the criticality search. Here’s how.
Run your regular base case of interest. Look at the output for the final value of the enrichment modification factor. You will find a edit like this near the bottom:
++++++++++++++++++++++++++++++++++++++++
+ +
+ COMPLETION OF FINAL SEARCH PROCEDURE +
+ +
++++++++++++++++++++++++++++++++++++++++
THE ENRICHMENT MODIFICATION FACTOR IS 2.36759E-01
THE BURN STEP TIME IS 2.10483E+02 DAYS.
Note the factor. You need to put it into your perturbed file.
Make a new rebus and MC**2 case with the perturbations you wanted. Decrease the sodium density, decrease the fuel density, eject a control rod, whatever.
In that new rebus input, go to the A.BURN card 4. You should see a 1.000 representing the desired k-eff at EOC. After that, there is a convergence criterion, probably set to 0.0001 or so. Change it to 1.000. This disables the criticality search.
The last two numbers in that same line are the first and second guesses of the new enrichment modification factor. Change the first one to the factor noted from the previous output file. Keep in mind that you can only put this number between certain columns. Check the manual to see which ones. Be careful with this!
If there is a burn cycle time search enabled as well, disable it in the same manner (on card 3 though) and insert the burn step time manually!
Now criticality search is off and you’ve manually set the critical class 1 enrichment. You’re ready to run. Run your new rebus case and compare k-effs with those from the base case.
Notes:
If you change a density somewhere, make sure it changes in the cross section library calculation too! The energy self shielding can vary wildly with different densities.
This method of calculating safety parameters should be taken with a grain of salt because it does not account for any anisotopies that you may see in real rod ejection accidents, etc. Diffusion theory is only an approximation of transport! Try using some perturbation theory codes like VARIANT if you want better results.
Have fun!
OK. What else? The new line search behaved very well. But in v5, the big case, the reactivity swings are all miniscule! 1.001 at BOC? Say what? Investigating. The core is breeding plutonium. It’s a breeder. Ah! Well the plenum had the wrong material, it looks like. I fixed it in the CORTANA input maker to agree nicely with the Hill cases of old and am now re-running just the first rebus case. This large case requires a very low guess of the enrichment modification factor.