CHI_D data missing -> assume delayed neutrons born in top group for materialfuel

[Olga Negri]

Hello!

I am very new to MOLTRES, I was trying to modify 'gen-mesh-one-material' tutorial to account for fuel velocity and precursor drift. I have received 

CHI_D data missing -> assume delayed neutrons born in top group for materialfuel

warning and a segmentation fault. I am not sure what I should do to fix this I would appreciate any advice and comments.

My input file is attached.

Looking forward to hearing from you!

Best regards,

Olga

[Alexander Lindsay]

On Thu, Feb 28, 2019 at 3:57 AM Olga Negri <olga....@gmail.com> wrote:

Hi Alex,

Thank you for your reply, your suggestions have fixed the problem.

I am trying to model a MSFR (so far in 2D only), a fast spectra MSR design.

One of the problems that I have faced now is that once I get the file to run, the variables would start changing, in this case increasing and then decreasing for both the groups and the temperature, and at a certain moment temperature would go back to it original value and any other parameters would not change with time as well. I am not sure what I am doing wrong there. Is that a common thing or am I doing something completely wrong? I have tried to do this with models containing moderator material and this has never happened.

I don't know how I dropped our mailing list in my first reply, but I'm adding it back here... So this is behavior that other users and I have encountered. I know that having too large of a time-step can cause this problem, but I believe you can also run into it in other situations. Could you share the input file that's generating this behavior? I can take a look at what might be happening.

Alex

Looking forward to hearing from you,

Best regards,

Olga

On 26 Feb 2019, at 05:41, Alexander Lindsay <alexlin...@gmail.com> wrote:

On Mon, Feb 25, 2019 at 4:52 AM Olga Negri <olga....@gmail.com> wrote:

Hello!

I am very new to MOLTRES, I was trying to modify 'gen-mesh-one-material' tutorial to account for fuel velocity and precursor drift. I have received 

CHI_D data missing -> assume delayed neutrons born in top group for materialfuel

warning

This is a warning and is not fatal. Presumably you are running in tests/nts and there are a bunch of files in there that look like msr2g_enrU*.txt. The warning is essentially saying there are no msr2g_enrU*CHID.txt files, e.g. there is no data about what energy groups delayed neutrons are born into. Since it doesn't have that data, moltres is just going to assume all delayed neutrons are going to be born into the highest energy group. If you don't want that to be the case, then you will need to provide the *CHID* data files.

and a segmentation fault. I am not sure what I should do to fix this I would appreciate any advice and comments.

The reason for the segmentation fault is that you have an EigenKernel in your kernels block (CoupledFissionEigenKernel) but you are not using an Eigen Executioner like NonlinearEigen or InversePowerMethod. You are using the Transient executioner. Either you can't use the CoupledFissionEigenKernel or you need to switch to using an Eigen executioner.

What is it that you're trying to ultimately accomplish? Maybe we can help direct you. Thanks for investigating Moltres!

Sincerely,

Alex

My input file is attached.

Looking forward to hearing from you!

Best regards,

Olga

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[Sun Myung Park]

Hi Olga,

I'm also currently trying to model the MSFR using Moltres. I have successfully managed to get a working, simplified model of the MSFR.

It seems like the issues you've faced are issues that I myself have encountered at some time. I would be happy to help you with the issues.

Best,

Sun Myung

[Olga Negri]

Hi Sun,

Thank you for your email!

I would appreciate any comments. I have attempted to build a 2D case of a MSFR and generated XS using SERPENT. While the cases similar to the MSRE example worked (the ones containing graphite moderator), a fast version was failing from the very start.

Is there anything different that you did that I am missing? Could it be the case that the generated XS are causing the problem? What did you use to generate your XS?

Best wishes,

Olga

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[Sun Myung Park]

Hi Olga,

I used SERPENT for my XS as well. Assuming your XS data is correct, these are some other potential causes for your issue:

1) The timestep size is too large.

This depends largely on your model and initial conditions. For me, an initial timestep of 1e-06 with 1.2x/0.4x adaptive timestep increment/cutback worked.

2) Incorrect mesh file. 

e.g. Check that there is heat transfer across interfaces.

3) Precursors

My model was unstable without precursors, as any nuclear reactor should be. Check that you have the "DelayedNeutronSource" kernel in your input file. It appears to be missing in the gen-mesh-one-material.i file that you linked previously.

Best,

Sun Myung

On Friday, May 31, 2019 at 8:57:06 PM UTC+8, Olga Negri wrote:

Hi Sun,

Thank you for your email!

I would appreciate any comments. I have attempted to build a 2D case of a MSFR and generated XS using SERPENT. While the cases similar to the MSRE example worked (the ones containing graphite moderator), a fast version was failing from the very start.

Is there anything different that you did that I am missing? Could it be the case that the generated XS are causing the problem? What did you use to generate your XS?

Best wishes,

Olga

On 18 May 2019, at 20:57, Sun Myung Park <smp...@illinois.edu> wrote:

Hi Olga,

I'm also currently trying to model the MSFR using Moltres. I have successfully managed to get a working, simplified model of the MSFR.

It seems like the issues you've faced are issues that I myself have encountered at some time. I would be happy to help you with the issues.

Best,

Sun Myung

On Monday, February 25, 2019 at 5:52:11 AM UTC-6, Olga Negri wrote:

Hello!

I am very new to MOLTRES, I was trying to modify 'gen-mesh-one-material' tutorial to account for fuel velocity and precursor drift. I have received 

CHI_D data missing -> assume delayed neutrons born in top group for materialfuel

warning and a segmentation fault. I am not sure what I should do to fix this I would appreciate any advice and comments.

My input file is attached.

Looking forward to hearing from you!

Best regards,

Olga

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