Under German licensing rules, irradiation-induced embrittlement of a reactor pressure vessel (RPV) in the core belt region is taken into account basically by determining the shift of the 41-J transition temperature of the Charpy impact energy versus temperature curve and then adjusting either the exclusion line of the modified Porse diagram, or the KIR curve, by this 41-J shift.

The accuracy limits of T ^{41 J}and Δ T ⁴¹ J determination are discussed and quantified. The transition temperature concept is shown to be conservative in the validity range of the respec-tive licensing rules because of the uncertainties in Δ T ^{41 J} determination.

Investigations with respect to irradiation effects on fracture toughness deserve high priority in current programs. Results from a A 533-B ² steel (HSST03) are presented, and the shift of the KIC curve is evaluated for two fluence levels.

Experiments related to the question of whether neutron flux density has an influence on embrittlement are briefly reported.