Struggle to validate Moltres results with OpenMC

[daffwwz]

Hi, I'm really new to the Moltres/MOOSE framework, and I aim to do a ULOFA transient simulation for SD-TMSR. The problem happened at the beginning when I tried just to validate the steady-state neutronic results with OpenMC. The keff I want to achieve with Moltres is near 1.00476, same as the OpenMC results, but what I achieved was always around 0.978. I don't know where the difference comes from since I already tried:

1. Refine the mesh of the reactor pin, the extruded part, and the peripheral part.
2. Changing the xsdata of the 6 group 6 delayed group (the particle number from 10000 to 1000000)

I'm assuming that there's a problem with the xsdata, since when I increased the number of precursor groups to 8, the beta_eff value for the 7th group is 2.5, but I also think the problem was in the input file that I was unaware of, since I'm not really familiar with this framework. Any help will be appreciated :D thanks!
eigen6g.zip

[smpark7]

Hi, for security reasons, I can't download the zip file. There are many reasons the keff from Moltres and OpenMC don't match:

1. User error in input files
2. Neutron diffusion performs poorly for your reactor geometry. keff discrepancies on the order of a few thousand pcm are common for many problems.
3. Unsuitable neutron energy group structure for the reactor. You can try running OpenMC in multigroup mode to quantify how much of the keff discrepancy arose from this issue.
4. Unconverged keff values in Moltres and/or OpenMC