Effect of iwt parameter on the covariance of the fission neutron yield (MF=31)

[AlexAimetta]

Dear NJOY community,

I am working on the production of multigroup covariance matrices with NJOY2016.78. I have noticed that the iwt parameter does not affect the covariance of the fission neutron yield (MF=31) in ERRORR. In other words, even if I use different iwt values, I always obtain the same fission neutron yield covariances. This is unlike the covariance of cross sections (MF=33), which values are modified according to the iwt parameter that I use.

Is this an expected behaviour? Anyone else has experienced the same issue? I would have expected the fission yield variance to depend on iwt too, but it seems that this is not true.

Thanks for the support and for the work that you are doing in developing NJOY.