The fracture mechanics behaviour of the WCLL blanket segment

The fracture mechanics behaviour is a limiting factor for the lifetime of a component, especially when the reduction of toughness of the structural material because of neutron irradiation effect is taken into account. In order to investigate the end of life behaviour of the WCLL blanket segment, a fracture mechanics analysis has been performed, evaluating the component both under normal operating and faulted conditions. The reference material used for this evaluation is the ferritic–martensitic chromium steel Z10 CDV Nb9.10 (AFNOR). From a general stress analysis on the whole component the most stressed areas have been found, on these areas reference cracks have been defined, depending on the stress classification and the component geometry. Under both the conditions the growth of the reference crack in the given stress field has been evaluated. The parameter to evaluate the criticality of the crack is the ‘J integral’, representing the energy required increase the crack length. From the available data, criteria have been developed to determine the allowable limit for this characteristic. A curve of the allowable value from 0 to 105 dpa has been produced. For normal and for faulted operating conditions it has been verified that the critical crack is greater than the allowable value. The dimensions of the critical crack have been evaluated with reference to the limits of the normal non-destructive test methods.