Unable to sample fission source - try explicit definition

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ahmed
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Unable to sample fission source - try explicit definition

Post by ahmed » Thu May 20, 2021 6:48 pm

hi

what this error meaning?

Sampling initial source...

***** Thu May 20 15:46:34 2021

Input error:

Unable to sample fission source - try explicit definition

Ana Jambrina
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Re: Unable to sample fission source - try explicit definition

Post by Ana Jambrina » Thu May 20, 2021 7:41 pm

Are you running a criticality calculation? The question to ask is: should it be a criticality calculation (simulating self-sustained chain reaction within the geometry) or an external source simulation?
If it is the former, check Unable to start or maintain a criticality source simulation. If it is the latter, change the simulation mode.
The solution to both of the above scenarios is to use an explicit source definition.
- Ana

ahmed
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Re: Unable to sample fission source - try explicit definition

Post by ahmed » Fri May 21, 2021 12:56 pm

Hi

Yes i am running a criticality calculation. I will try to run with an external source simulation

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Jaakko Leppänen
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Re: Unable to sample fission source - try explicit definition

Post by Jaakko Leppänen » Mon May 24, 2021 9:20 am

The error message basically means that Serpent is unable to locate enough source points by random sampling. The most common case where this occurs is when you are running a standard criticality source simulation, but the fissile material covers only a small fraction of the geometry. Serpent samples random points throughout the geometry, and selects points that land on fissile materials as a source. If the probability of landing a point on such material is low, the sampling fails.

The solution is to put a bounding box around your fissile zone using the dx, dy and dz options of the source card. This should increase the probability of accepting the points and get the simulation going.
- Jaakko

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