MODELING THE BEHAVIOR OF A CONTROL-ELEMENT BLADE DURING IRRADIATION

The control-rod elements in a boiling-water reactor contain natural bo ron carbide (B4C) powder, used as neutron-absorber material and clad i n stainless-steel blades. During in-reactor service, the internal prod uction of helium gas and point defects in neutron-irradiated boron car bide cause swelling which can induce significant contact stresses in t he blade causing, eventually, stress-corrosion cracking of the blades. In this work, a finite-element analysis of a control-rod blade consis ting of B4C powder and stainless-steel cladding has been performed usi ng ADINA. An algorithm for the finite-element calculation of a porous material such as B4C powder has been developed and which models both s welling and consolidation behaviour of B4C powder. The Drucker-Prager constitutive law has been used to model the consolidation effect. The model has been verified with an analytical solution for a simple geome try. A number of cases with B4C powder in contact with stainless steel and using the actual blade design have been studied for which contact stresses, the displacements and the effective stresses are calculated . Finally, the model has been used to predict the deformation of the b lade during irradiation under B4C swelling and irradiation-induced cre ep of stainless steel. (C) 1997 Published by Elsevier Science Ltd.