How to use MCNP to calculate power distribution for a reactor core?

[gsyou]

Assume no boron and all control rods out, so the core is super-critical. if KCODE mode is used, and F4 card is for tally the neutron for each assamblies. Can the results represent the power distribution of the core, whether the multiply-factor can affect.
the results i get (power distribution), for the assamblies in the middle of the core is bigger than the references, and for the assamblies on the side of the core is smaller than the references. it looks like something wrong, and I can not find what is wrong. Please Help Me.

 

[gsyou]

now I use F4 card and (Fm4 -1 m -6) card to tally the power distribution. Much better than using F4 card alone. Anybody can conform that for me? Thank you!