SPACE-DEPENDENT RESONANCE SELF-SHIELDING

A new method is developed to determine space-dependent, self-shielded cross sections for resonance nuclides with no overlapping resonances, contained in an arbitrarily shaped absorber body within some general l attice configuration. The theoretical basis for the method is discusse d, and analytical expressions are presented for the space-dependent fl ux spectrum in the vicinity of an isolated resonance and for the space -dependent variation in the shielded resonance integral and multigroup cross section. The shielded cross-section expressions contain space-d ependent, ''weighted escape probabilities'' that correspond to the wei ghted average of the energy-dependent escape probability over each ene rgy group. The method is implemented in an assembly lattice physics co de, and results are compared to those obtained with a highly accurate transport theory calculation that uses pointwise cross-section data. T he method gives good agreement for the radial variation in the self-sh ielded cross section through a boiling water reactor fuel pellet.