PROBLEM neutron_diffusion 3D
READ_MESH bunny.msh

nu1 = 2.4
Sigma_f1 = 0.08
nuSigma_f1 = nu1*Sigma_f1
Sigma_s1.1 = 0.22
Sigma_t1   = 0.4

chi[1] = 1.0

BC base  vacuum 
BC rest  vacuum 

SOLVE_PROBLEM
PRINT keff-1.029
WRITE_RESULTS