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require special treatment of several terms in the multigroup diffusion equation. Using notation similar to that of Baller (24), the multigroup diffusion equation is

                                     N
  - DiV2i (r) +  ti i() = xiS(r) +       ,. i (r)
                  1                 j=l
                                    j 7i
                                                   (2.4)

where

                               N
             E a~ + D.iB. 2 +IE     i-i
             ti=Ei   i        j=lsij
                 1             4


          S( )   X    (Vxf~ ii(r
                 .i=l


for 1 < i < N,   N = number of groups. The symbols are defined as


         i(r) = neutron flux in i-th group at position r

            D. = diffusion coefficient for the i-th group
            1

            E t.= total removal from i-th group


            E .= absorption cross section for the i-th
            a.
            1    group
            B.2= transverse buckling for the i-th group


         s,i+j = scattering from group i to group j

            Xi = integral of the fission spectrum over the
                 energy range represented by group i