## Question: I want to implement a boron curve in my burnup calculations

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BlairPBromley
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### Question: I want to implement a boron curve in my burnup calculations

Here's the problem:

I am modeling a PWR 17x17 fuel assembly.

I am doing a burnup/depletion calculation, using the following cards (as an illustrative example)
set powdens 0.015 % 0.015 MW/kg, 15 kW/kg
dep butot
0.000015 % Burnup Step # 1 from 0 MWd/kg to 0.000015 MWd/kg

set powdens 0.015 % 0.015 MW/kg, 15 kW/kg
dep butot
0.00015 % Burnup Step # 2 from 0.000015 MWd/kg to 0.00015 MWd/kg

set powdens 0.015 % 0.015 MW/kg, 15 kW/kg
dep butot
0.0003 % Burnup Step # 3 from 0.00015 MWd/kg to 0.0003 MWd/kg

set powdens 0.015 % 0.015 MW/kg, 15 kW/kg
mix cool % 3299.959 ppm of Boron in Water
dep butot
0.0009 % Burnup Step # 4 from 0.0003 MWd/kg to 0.0009 MWd/kg

The cards above illustrate the first 4 steps.
In reality, I am setting up 40 steps, to do burnup up to a max value of 70 MWd/kg.

In the example shown, I'm using a constant specific power, of 15 kW/kg (0.015 kW/g) for each burnup step.
However, I am assuming that I have the freedom and the option to change the specific power at each burnup step
by implementing the "powdens" card before each burnup step.

Thus, if I want to have a time-dependent power history for my burnup calculations, I should be able to do it.

However, what I am really interested in doing, is to change the boron concentration (in the coolant, made of water) at each burnup step.

In the previous version of SERPENT (Version 1.0), this burnup-dependent boron concentration could be implemented quite simply using the
"set abs" card, which looked something like this:

set powdens 0.015 % 0.015 MW/kg, 15 kW/kg
set abs boron -0.0033 water % 3300 ppm of Boron in Water
dep butot
0.000015 % Burnup Step # 1 from 0 MWd/kg to 0.000015 MWd/kg
%

HOWEVER, Serpent 2.0 does not have the "set abs" card option.

How else can I do what I want to do, but in a very simple way?

Do not want to do any "branch" calculations. I just want to be able to use a different boron concentration in my coolant at each burnup step.

Thanks

Blair Bromley

Jaakko Leppänen
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### Re: Question: I want to implement a boron curve in my burnup calculations

You can do a critical boron calculation using the iter nuc option:

http://serpent.vtt.fi/mediawiki/index.p ... t_iter_nuc

but if you pre-determined concentrations, then the only option is to divide the calculation in multiple parts and use the restart files with rfw and rfr.
- Jaakko

BlairPBromley
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### Re: Question: I want to implement a boron curve in my burnup calculations

Thanks Jaako.

Much appreciated.

Does this mean that if I use this card, will the SERPENT calculation compute the critical boron concentration after each burnup step, and dump that information into the output file?

Does this also mean that the burnup calculation will be performed using the critical boron level at each burnup step, instead of some constant nominal value?...such as 500 ppm Boron?

I want be able to use the correct "history" for the fuel. I suppose using the critical boron concentration for burnup calculations is somewhat analogous to using the critical buckling...which is very typical for deterministic lattice physics codes (such as CASMO, WIMS10, DRAGON, and others).

Thanks again. A few more answers to help clarify details would be greatly appreciated.

Sincerely,

Blair Bromley

Riku Tuominen
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### Re: Question: I want to implement a boron curve in my burnup calculations

BlairPBromley
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### Re: Question: I want to implement a boron curve in my burnup calculations

Many thanks Riku.

We will definitely test this approach.

However, I do have an underlying question.
I
Once the "critical" density of the particular material....in this case the boron concentration, is determined, then will this modified boron concentration then be used in the subsequent burnup step?

Otherwise, will all of my burnup calculation steps be performed using the same initial boron concentration that I had specified at time = 0, burnup = 0?

What I want to do is to perform each burnup calculation step using the critical boron concentration determined at a given burnup step.

Perhaps I will need to use the methodology that you and Jaako suggested, to get an initial estimate of the CBC, then use the restart option to implement the modified boron concentration at each burnup step.

Thanks again for your suggestions and insights.

Sincerely,

Blair Bromley

Jaakko Leppänen
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### Re: Question: I want to implement a boron curve in my burnup calculations

The iteration is applied for all steps separately. So your reactor will remain critical throughout the cycle.
- Jaakko

BlairPBromley
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### Re: Question: I want to implement a boron curve in my burnup calculations

Thanks Jaako.

Is the burnup calculation at each burnup step performed using the critical boron concentration computed at each step?

Is the answer to the above question "yes", or is the answer "no"?

Sorry if this seems like a stupid question, or if it seems like I am asking the same question over and over.

Sincerely,

Blair Bromley

Jaakko Leppänen
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### Re: Question: I want to implement a boron curve in my burnup calculations

The iteration is applied separately for each step, so yes, each burnup step is calculated using critical boron concentration.
- Jaakko

BlairPBromley
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### Re: Question: I want to implement a boron curve in my burnup calculations

Dear Jaako,

Thanks! This answer is perfect. Exactly what I needed to know.

Much appreciated.

Sincerely,

Blair