PERFORMANCE MODELING OF NEUTRON ABSORBERS

A computer code to predict the performance of fast reactor control rods has been developed and used to analyze the integrated behavior of a proposed FTR-type control rod in Row 2 of EBR-II. In particular, the influence of the B**1**0 enrichment and solid reaction product swelling have been considered. It is noted that control rod claddings are predicted to begin rapid plastic strain very shortly after the fabricated gap between the absorber pellets and the cladding has closed, due to high contact pressure which develops with continued pellet swelling. Models for helium gas bubble swelling and release are presented, which suggest minimum swelling from this source at about 1000 degree C.