Help calculating angular distributions in Pu239 with ENDFVIII data

[sombrereau]

NJOY team,

I'm a very new NJOY user. I'm trying to generate the covariance data with NJOY to calculate the nuclear data uncertainty for a potential Plutonium Fueled Experimental Nuclear Reactor.

I'm getting errors when I try to process the ENDFVIII Pu239 nuclear data. NJOY fails to create tapes for covariance of angular distribution.

NJOY issues a message related to this issue in the reconr module

---message from rdf2bw---calculation of angular distribution not installed.

and another that actually stops the calculation:

error` in findf mat9437 mf 3 mt251 (mu average cosine of the angle for elastic scattering (lab system)) not on tape 18

I'm running NJOY21 v. 1.1.1. I'm using nuclear data downloaded from the IAEA website (https://www-nds.iaea.org/public/download-endf/ENDF-B-VIII.0/n/n_9437_94-Pu-239.zip | copied as tape20) and I'm using the attached input file.

Thanks for any tips,

-Tommy Cisneros

[whaeck]

Hi,

The warning message coming out of reconr that you mention above (calculation of angular distribution not installed) is not something to be worried about. This has to do with an experimental capability in NJOY to calculate angular distributions from the resonance parameters. It has to be enabled at compile time (it is switched off by default since it interferes with too many other modules).

The second message is most likely due to the average mubar not being calculated in your groupr run. When asking for automatic mfd processing (which you are doing with 3/), some mfd mtd paires still need to be specified in order to get them. You should add the following mfd/mtd in groupr:

3 251 'mubar' /

As an example, I can refer you to test 15 which does almost the same as what you're trying to do.

Best regards,
Wim

[sombrereau]

@whaeck,

Thanks so much for your response!

So I added the 251 by itself and that failed to produce the covariance tape, but I looked in test 15 and added all the reactions that were in that example and the tape for covariance of the angular distributions looks like its now functioning. -- here is my
updated input file.

...

Now, the errorr run to produce the covariance of the fission neutron emission spectrum is not finishing.

---message from errorr---mf35 processing with the mf5 spectrum vector

error in colapsnot coded for multiple sigma zeroes or legendre orders.

STOP 77

Do you have any more recommendations?

-Tommy

[whaeck]

OK, so that's a weird one. I checked the input and it looks fine to me. Even your tape91 look OK but for some reason it get rejected in your last errorr run. The weirdness about it is that if I remove the errorr run for MF34, it suddenly works without an issue - and I have no idea why.

So, to solve it for now: just run mf35 in a separate input file.

[sombrereau]

I can do that ... I was just worried some that, it was a sign something else wasn't working right.

Thanks so much for your help!

[nathangibson14]

We do need to figure out what's going on with MF34 processing, as this one is very strange. I don't have reason to suspect that MF34 is outputting incorrect data, but it's probably worth treading a bit carefully with that data regardless.

But your other option in the mean time is to process MF35 before MF34, and then you can still use one file 😄

[sombrereau]

This sounds like I need to open a ticket and be ready to update the covariance matrix and re run MY calc if/when the MF34 tape changes.

-Tommy