  We compute the representations (``nimreps'') of the fusion algebra of affine
sl(N), which determine the boundary conditions of sl(N) WZW theories twisted by
the charge conjugation. This is done following two procedures, one of general
validity, the other specific to the problem at hand. The problem is related to
the classical problem of decomposition of the fundamental representations of
sl(N) onto representations of $B_l=so(2l+1)$ or $C_l =sp(2l)$ algebras. The
relevant nimreps and their diagonalisation matrix are thus expressed in terms
of modular data of the affine B or C algebras
