adjusting heavy water concentration in moderator

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tarek
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adjusting heavy water concentration in moderator

Post by tarek » Tue Sep 22, 2020 10:58 pm

Hello
Is there any way to adjust boron concentration or heavy water concentration in moderator during burnup steps , ex : after how many burnup steps days or MWD/T needed to adjust H3BO3 OR D2O concentration in moderator to retain K-inf again to unity ?
Thanks in advance

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Jaakko Leppänen
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Re: adjusting heavy water concentration in moderator

Post by Jaakko Leppänen » Wed Sep 23, 2020 9:02 am

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Vahir
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Re: adjusting heavy water concentration in moderator

Post by Vahir » Sun Oct 04, 2020 4:15 am

Is there a way to impose a boron concentration after a certain level of burnup? In the 2015 manual, this is done through 'set abs' declarations in between busteps, but this does not appear to work.

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Re: adjusting heavy water concentration in moderator

Post by Ana Jambrina » Sun Oct 04, 2020 12:39 pm

“abs” option is not available/included in Serpent 2.
The alternatives are: make use of the “iter nuc” option, as suggested in the previous post, if targeting a k-eff value; or, if fixed/pre-determined concentrations want to be used instead, then the option is to divide the calculation in several parts: which can be done by using the “rfw/rfr” options - restart files.
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Re: adjusting heavy water concentration in moderator

Post by Vahir » Tue Oct 06, 2020 4:14 am

Ana Jambrina wrote:
Sun Oct 04, 2020 12:39 pm
“abs” option is not available/included in Serpent 2.
The alternatives are: make use of the “iter nuc” option, as suggested in the previous post, if targeting a k-eff value; or, if fixed/pre-determined concentrations want to be used instead, then the option is to divide the calculation in several parts: which can be done by using the “rfw/rfr” options - restart files.
rfw/rfr seems to be exactly what I'm looking for. Could you elaborate on how the restart files work? I would imagine they are simply definitions of materials with the associated burnup step, but I'm unsure as to how to structure one exactly.

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Re: adjusting heavy water concentration in moderator

Post by Jaakko Leppänen » Tue Oct 06, 2020 10:19 am

The restart files contain the compositions of your burnable materials. There is no need to adjust them when changing the composition of water. You simply stop the burnup calculation at the point where want the change to be applied, make the corresponding adjustment in the input file, and restart the burnup calculation from the point it was left off.
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Re: adjusting heavy water concentration in moderator

Post by Staffan F » Thu Apr 08, 2021 5:30 pm

Jaakko Leppänen wrote:
Tue Oct 06, 2020 10:19 am
The restart files contain the compositions of your burnable materials. There is no need to adjust them when changing the composition of water. You simply stop the burnup calculation at the point where want the change to be applied, make the corresponding adjustment in the input file, and restart the burnup calculation from the point it was left off.
I am a Master student and I am going to simulate a assembly during its life in a PWR-reactor and I have exactly the same problem with adjusting the boron concentration. Sinc there was an option for this in Serpent 1 with example in the manual from 2015 it would be nice with some simple example of this since it is rather common situation i real simulations. The set abs option was very simple to understand and now one need much more effort to achieve the same result.

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Re: adjusting heavy water concentration in moderator

Post by Ana Jambrina » Thu Apr 08, 2021 5:46 pm

Nuclide iteration for boron is quite straight-forward: see 'iter nuc' option Then, e.g., given that you have defined a coolant material ‘cool’ with 50100 50110 isotopes in it (B-10, B-11 respectively) - to be included in the iteration to achieve a given target, k-eff =1.0, where the extra inactive cycles to run the convergence iteration are set, e.g., to 50: --> set iter nuc 50 1.0 2 50100 50110 1 cool

Given the initial boron concentration for the coolant material (e.g. ppm of boron) and the output parameter ‘ITER_FACTOR’, scaling factor, (from the ‘_res.m’ file) you can obtain the boron concentration in the coolant material at each depletion state point.

For further information about how critical density iteration works, check critical density iteration (input/output syntax and methodology description).

Note: analogous to the ‘abs’ option in Serpent 1, the ‘mix’ option in Serpent 2 is available to set a homogeneous mixture of several materials: e.g. set abs boron -650E-6 water (Serpent 1) --> mix cool water -0.999350 boron -650E-6 (Serpent 2). - For a practical example of 'mix' option: automated burnup sequence. Additionally, '-mix' command line option, it might help you out to set up material mixtures.
The main difference is that only the initial value (boron concentration) is set, then: if you chose to use the 'iter nuc' option, the boron concentration would be adjusted automatically (through a convergence iteration process towards a target k-eff) during the depletion calculation. If instead of letting Serpent evaluate the (critical) boron calculation by itself you would like to imposed certain value, you would need to use the restart feature 'rfw'/'rfr' to restart every burnup-step the calculation and modify the boron concentration (e.g. 'mix' parameters) manually.
- Ana

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Re: adjusting heavy water concentration in moderator

Post by Staffan F » Fri Apr 09, 2021 4:18 pm

I think I was a bit unclear about my simulation goals. My work is a real case study. I am not interested in achieving criticality by adjusting the boron concentration. I have an real, existing PWR fuel assembly which has been irradiated during 5 fuelcycles in a reactor with reshuffling of the assembly between each cycle. In total I have 88 burnup steps where the steps are in daysteps(roughly 9-19 steps/cycle). I have 5 inputfiles(one for each fuelcycle) and use the rfw/rfr method to transfer information between them, but with 88 burnups steps this method is to complicated for the boron concentration. What I need is exactly what is written as an burnup example in the end of chapter 8 in the Serpent 1 manual from 2012( see below). In the old Serpent 1 style I could have muliple set abs definitions in the same inputfile. When I try to use multiple mix commands like the set abs in the example, it does not work.
I have tried the rfw/rfr method but I can't find a method to stop the Serpent execution_(rfr/rfw does only write and read) without using the branch/coeff cards which makes my burnup calculation too complicated.

From Serpent 1 manual:
% --- Cycle 1: 650 ppm boron, final burnup 13.5 MWd/kgU
set powdens 40.0E-3
set abs boron -650E-6 water
dep bustep
0.10000
.
.
.
0.50000
% --- Downtime for 80 days:
set powdens 0.0
set abs boron -650E-6 water
dep daystep 808.7 Burnup calculation examples 123
% --- Cycle 2: 300 ppm boron, final burnup 25.0 MWd/kgU
set powdens 40.0E-3
set abs boron -300E-6 water
dep bustep
0.50000
.
.
.
5.00000
% --- Downtime for 80 days:
set powdens 0.0
set abs boron -300E-6 water
dep daystep 80

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Re: adjusting heavy water concentration in moderator

Post by Ana Jambrina » Fri Apr 09, 2021 4:37 pm

There is not a similar option as 'abs' in Serpent 2 (the manual refers to Serpent 1, which might be outdated).

If you want to set a fixed boron concentration you have to modify such value - either through a single material definition through ‘mat’ card or a mixture ‘mix’ option at each step where the change happens (single ‘mix’ option per material).

In order to do it, there are two options:

Option 1: sequential use of ‘rfw’/‘rfr’ restart feature, and manually change the boron concentration - where instead of running the full depletion history just at once, the calculation is split, following the boron concentration changes:
- set the initial boron concentration + ‘rfw’ option —> run a depletion calculation until the burnup step where the boron concentration needs to be changed.
- set new boron concentration + ‘rfr’ option specifying the burnup point where the calculation was left-off (previous burnup step) + ‘rfw’ option (to generate a new restart file) —> …
[With the previously described approach you could obtain same results than setting a historical variation sequence/branch to automatise the process, where the automated burnup sequence would perform a restart for each listed burnup point looping over the branch combinations/variations.]

Note: given that you have a large number of burnup-steps and assuming you might want to change the boron concentration at each of them, you might want to write a script to run Serpent sequentially: prepare the set of input files with the different boron concentrations and the subsequent 'rfw'/'rfr' options for each burnup point - in this way, once one calculation is done, automatically the next one would be launched with the new input parameters and previously created restart file.

Option 2: historical variation ‘hisv’ card, which activates a linked ‘branch’ card after a specific burnup, allowing e.g. general changes during the depletion history, such in this case, replacing a material: ‘repm’ option (defined by a single ‘mat’ card or a mixture ‘mix) - see automated burnup sequence.
- Ana

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